Evidence-based Prosthodontics by Nay Aung

Evidence-based Prosthodontics

6 Prognosis and Evidence Based Prosthodontics a s B jö r n j o k s ta d

INTRODUCTION The word prognosis is deriveed from Greek, and literally means fore-knowing or foreseeing. Physicians coined the term in the 17th century for a prediction of the most probable prospect for the patient based on the patient’s signs and symptoms. We may imagine that the “prognosticators” at that time were aware of the negative effects of e.g. undernutrition, old age and co-morbidity due to concomitant diseases on the patient’s chances for improvement. Using current nomenclature, we would call these attributes for “prognostic factors”. Today, the term “prognostic factor” is used for any intrinsic or extrinsic characteristic that can be associated with a likely outcome of a condition. This differs from the term “risk factor”, which is used for characteristics that may be associated with the initiation of a condition or a disease. Neither prognostic factors nor risk factors necessarily entail a cause and effect relationship nor is there any consensus about what constitutes the numerical thresholds between “strong/significant” and “weak/unimportant”. Risk factors and prognostic factors can have various qualities: They may be disease-specific, they may constitute a state of co-morbidity,

Differences

Risk factors

Prognostic factors

Factors, associ-

…an increased risk of

…a worsening of a condition

ated with…

developing a condition or disease

Study population

…healthy individuals

consists of …

…individuals with a condition or disease

The event of in-

…onset of a condi-

… consequences of a con-

terest is the…

tion or disease

dition or disease

Rates usually

… rare events that may take

… more frequent events that develop

predict…

a long time to happen

over a relatively short period of time

Table 6:1. Some differences between risk factors and prognostic factors

Prognosis and Evidence Based Prosthodontics

or they may consist in a demographic factor etc. Risk factors and prognostic factors may be similar, but not necessarily of similar predictive strength nor direction. E.g., men have a significantly higher risk for myocardial infarct than women, but the prognosis is relatively good. For women it is the opposite; myocardial infarcts are infrequent, but when they do occur, the morbidity and mortality is significantly greater than in men. Another difference is that risk factors usually predict low probabilities of an event that may take a long time to appear, Level

Prognosis

• Systematic Review with homogeneity* of inception cohort studies • Algorithms /scoring systems which lead to a prognostic estimation validated in different populations

• Individual inception cohort study with > 80% follow-up • Algorithms /scoring systems which lead to a prognostic estimation validated in a single population

• All or none case-series

• Systematic Review with homogeneity* of retrospective cohort studies • Systematic Review with homogeneity* of untreated control groups in Randomized Controlled Trials

• Retrospective cohort study • Follow-up of untreated control patients in a Randomized Controlled Trial • Derivation of algorithms/scoring systems which lead to a prognostic estimation or validated on split-sample only (i.e. collecting all the information in a single segment, and then artificially dividing this into “derivation” and “validation” samples.)

• “Outcomes” research (Clinical evaluations that focus on 1) the status of participants after receiving care and on 2) the process of care itself)

• Case-series

• Prognostic cohort studies of poor quality (i.e. sampling was biased in favour of patients who already had the target outcome, or the measurement of outcomes was accomplished in <80% of study patients, or outcomes were determined in an unblinded, non-objective way, or there was no correction for confounding factors.)

• Expert opinion without explicit critical appraisal • Expert opinion based on physiology • Bench research • Pathophysiological principles used to determine clinical practice

Table 6: 2 . Levels of Evidence according to the Oxford Centre for Evidence-based Medicine (http://www.cebm. net/?o=1025). * Free of variations (heterogeneity) in the directions and degrees of results between individual studies which may raise doubt about conclusions of the review.

Prognosis and Evidence Based Prosthodontics

while prognostic factors often are associated with events that are more frequent. Risk factors are consequently often appraised through case-control study designs, while prognostic factors are identified by means of a range of study designs beyond prospective cohort studies. Moreover, while the outcome of interest for risk factors is the onset or implications of a health condition or disease, the outcome of interest for evaluating prognostic factors may range from recovery to the disease recurring or a range of medical complications and even death (Table 6:1). The term prognosis is today being used within all fields of biomedicine and denotes a prediction of how a patient’s disease will progress, and whether there is chance of recovery with and without active intervention. Sometimes, the term “natural history” is used to describe the prognosis of disease without medical intervention, while the term “clinical course” of a disease describes a change in prognosis of the disease that has come under medical management. An active medical intervention can be considered as one prognostic factor amongst several other prognostic factors. This can perhaps be understood using cancer treatment and survival as an example. Besides age, gender and cancer invasiveness, active interventions are each separately, as well as possibly synergistically identified as prognostic factors for patient survival. Active interventions might be a surgical operation technique and/or supplemented with x Gray of radiation therapy and/or supplemented with chemotherapy and/or strict dietary regimes and/or smoking-cessation interventions and/or mental or physical exercise etc. From a hypothetico-deductive reasoning perspective, risk and prognostic factors can be regarded as similar, and they are inferred from the data of studies of different methodological designs. Multiple clinical study designs can be applied to identify potential prognostic factors, but the risk of bias will depend on the choice of study design. The Oxford Centre for Evidence-based Medicine has suggested a hierarchy of levels of evidence for estimating prognosis that seems to have obtained general consensus amongst scientists and clinicians (Table 6:2).

Prosthodontic therapy

tionally is central in an evaluation

Prosthodontic therapy is characterized

of prognosis is poorly defined.

by certain traits that make the applica-

2. It is not uncommon to regard the spe-

tion of the different terms described

cific removable prosthesis as the core

in the previous section complicated

of the therapy. The prosthesis, howev-

in a traditional medical context:

er, should rather be regarded as one of

1. Removable prostheses are being

several means to resolve the patient’s

used as replacements for oral tissues

afflictions due to lack of teeth, and

with a wide spectrum of reasons

expected to have a minimal impact on

for loss of teeth. This means that

eventual further disease progression.

the disease condition that tradi-

3. It is advocated and presumed that

Prognosis and Evidence Based Prosthodontics

a removable prosthesis should first

ered a risk factor for both caries and peri-

be inserted after a causal therapy

odontitis of the remaining teeth in order

has been instituted and following

of magnitude from the abutment teeth,

a return to acceptable oral health

the teeth covered or adjacent to the pros-

and optimal biological condition

thesis and the remaining dentition. The

of the remaining tissues. Reality,

design and ability of the individual com-

unfortunately, is that prostheses

ponents to resist mechanical breakdown

often are adapted where such ideal

is an additional dimension. Concurrently,

conditions seldom are obtained.

the RDP design and remaining integrity

4. The patients’ objectives for acquir-

is a prognostic factor as regards negative

ing a removable prosthesis will

outcome such as an unstable occlusion

differ, and an estimate of prog-

or oral discomfort, or regarding positive

nosis will therefore build on dif-

outcome such as satisfactory aesthetics,

ferent combinations of criteria.

speech and mastication. Moreover, this

5. The technical quality of the remov-

dual perspective of removable prostheses

able prosthesis as well as the resistance

can also be attributed to the past uncer-

of the individual components to with-

tainties of aetiology of several oral diseas-

stand wear, discoloration and break-

es and afflictions. E.g. temporomandibu-

age will clearly affect the prognosis.

lar dysfunction (TMD) and even bruxism

Indirectly, the clinician’s competency

was previously believed to be caused by

and proficiency as well as ability to

lack of posterior teeth or “instable occlu-

prescribe an adequate treatment plan

sions according to a set of criteria”, and as

are additional confounding variables.

such a partial removable dental prosthesis

6. Finally, several observations indicate

was regarded as a prognostic factor to alle-

that patients’ somatic and psychologi-

viate the diseases. Today, there is general

cal adaptation ability to a removable

consensus that such a relationship is at

prosthesis as a foreign intraoral object

best weak or non-existent. Nevertheless,

will vary greatly, and this important

an incorrectly designed removable den-

factor for prosthodontic treatment

ture can certainly induce TMD and must

success can hardly be predicted be-

therefore rather be regarded as a risk fac-

fore commencing the therapy.

tor in this perspective. The same applies to our current understanding of residual

It is difficult to employ a rigid separation

ridge resorption, which is a physiological

between prognostic factors and risk fac-

remodelling process following tooth ex-

tors when they are applied to removable

tractions where the relevance of the de-

prostheses. All removable prostheses per

sign and/or diurnal use of the removable

se increase the risk for the development of

denture as a potential risk factor for ac-

new oral diseases. Thus, a partial remova-

celerated local jaw bone loss still remains

ble dental prosthesis (RDP) can be consid-

unsolved following decades of debate.

Prognosis and Evidence Based Prosthodontics

in the prosthodontic literature applied

Prognosis, general considerations

not only in the context of describing

As clinicians, we are faced with con-

the natural history and clinical course of

siderations of prognosis continuously.

diseases, but also used to describe their

The patient may sometimes ask the direct

possible adverse consequences on remain-

question: “How long can I expect my new

ing oral tissues as well as ability to satisfy

removable prosthesis to last?” This question

the patient’s subjective needs and finally

contains three elements; (1) a time aspect

the durability of prostheses of different

(when), (2) a qualitative element (what)

designs. The philologist may correctly

and (3) a quantitative estimate (probabil-

point out incongruent uses of the term in

ity). In relation to removable prostheses,

prosthodontics papers, e.g., “prognosis of

it is not uncommon to consider and dis-

osseointegrated implants” and even in com-

cuss the durability for specific forms of

prehensive dictionaries such as the Glos-

prostheses, e.g., partial prostheses made

sary of Prosthodontic Terms (edition 4):

for Kennedy class 1 versus 4 situations,

”denture prognosis: an opinion or judgment

full versus partial prostheses, implant

given in advance of treatment for the pros-

supported versus tooth retained, etc.,

pects for success in the fabrication of dentures

as a rough estimate for prognosis. This

and for their usefulness”, and (edition 7):

is, however, only one component of the

“Preprosthetic surgery: surgical procedures de-

foundation we need to build on when

signed to facilitate fabrication or to improve

we estimate the prognosis of different

the prognosis of prosthodontic care”. Further

therapy alternatives. More important is

examples of how the term prognosis is

the need to elucidate the patient’s past

being applied within the field of prostho-

and current medical and dental histories

dontics are e.g. as “probability of reaching a

in combination with a comprehensive

predetermined objective of a therapy” or “to

evaluation of oral status and relevant

what extent patient satisfaction is obtained”.

medical elements and integrate these

To summarize, the term prognosis is

The intention of this review is not to

findings with the patient’s subjective

completely befuddle the reader, but rather

needs and preferences. Not until we have

to point out that the word “prognosis” is

conducted these procedures will it be pos-

an example of a term that is used without

sible to apply the true term of informed

knowledge of the etymology of the term

consent. As health care providers we must

nor its precise definition or general con-

ask ourselves if there is a benefit or need

sensus for use. One cannot say that one

for any interventions at all. One example

or the other usage of the term prognosis

is an elderly person, with a substantially

is incorrect, as long as it’s made under-

worn, but otherwise problem free, denti-

standable in context with other words.

tion. What will happen, or likely fail to develop with or without an e.g., tooth borne prosthesis that augments the ver-

Prognosis and Evidence Based Prosthodontics

tical dimension of occlusion? A tenta-

• How will the functions of the stoma-

tive answer to a patient’s inquiry must

tognathic system change with or

build on past and current presence of oral disease, expected wear progression

without this prosthetic therapy? • How will the patient centered

and expected biological response to the

outcomes, e.g. aesthetics, func-

removable prosthesis as an intraoral for-

tion or comfort, change with or

eign object. Aspects that are important to

without this prosthetic therapy?

evaluate in this context are for example: • What will happen with the quality

• What will happen with an already existing prosthesis, if

of the remaining tissues, including

this is the case, with or with-

eventual remaining teeth, with or

out this prosthetic therapy?

without this prosthetic therapy?

Reference: Risk factor Caries & Periodontitis

Öwall et al., 2002 Wöstmann et al., 2005

Mucosal injury

Creugers & Kreulen, 2003

• Allergy • Stomatitis • Hyperplasia • Burning mouth syndrome Temporomandibular dysfunction

De Boever et al., 2000

Prognostic factor Occlusal stability (“tooth malpositions”)

Celebić & Knezović-Zlatarić, 2003

Bone remodeling (“Alveolar bone loss”)

Palmqvist et al., 2003

“Oral discomfort” (esthetics, mastication, speech, etc.)

Gotfredsen & Walls, 2007

Nutritional aspects

N’gom & Woda, 2002

Quality of life

Strassburger et al., 2006

Patient satisfaction

Zlataric & Celebic, 2001

Technical quality deterioration

Grundström et al., 2001

Table 6:3. Key references with focus on function period and technical quality of the removable prosthesis (i) in context to potential risk factors for future disease or (ii) as prognostic factors for impact on oral discomfort and/or disease, or (iii) as a function of time.

Prognosis and Evidence Based Prosthodontics

Thus, discussions about the prognostic

tial threats against the integrity of the

elements of prosthodontic therapy have

remaining tissues, against the dentition’s

to encompass different perspectives.

attempted/expected functional quali-

The actual fate of the prosthesis is just

ties, and against patient “oral comfort”

one element of these considerations:

defined qualities need to be identi-

1. Qualitative (what can happen over

fied and addressed in order to provide

time?, i.e., “an (adverse) event”) 2. Time factor, i.e., the time to an (adverse) event 3. Quantitative (what is the prob-

meaningful prognostic estimates to the patient in a comprehensible manner. Moreover, the technical quality of prosthesis and its individual components,

ability that a certain (ad-

and the ability of each component to

verse) event will develop?)

resist wear and tear, are additional con-

4. Observation viewpoint (therapy defined disease versus patient experienced illness?) 5. Documented estimations on progno-

founding elements in this context. Technical and biological problems may be easy or difficult to identify. Both prostheses that function adequately in

sis (aggregated data from published

all ways, and the opposite, a prosthesis

studies of populations versus the

that is damaged beyond usability, are

individual clinician and patient?)

easy to detect, although the reasons

Qualitative (what can happen over time?)

for the damage can be debatable. Between these two extremes there is a wide spectrum of therapy results that

A long list of clinical signs and symp-

can be more or less difficult to identify

toms is considered in prosthodontic

or acknowledge and where the examiner

therapy in context with prognosis. Typ-

must use clinical judgment to establish

ical measures are a selection of usual

how adverse events can be registered.

problems encountered in prosthodontic

When evaluating reports on prognosis

patient groups. They are categorized as

or if planning a new clinical trial with

technical, related to the actual prostho-

the objective to determine prognosis it

dontic construction, or biological, that

is important to recognize some thumb

is, development of new oral disease or

rules. A potential for bias is introduced if

return of previous oral disease, which

a prognosis is based on a subjective ap-

from more or less reliable criteria can

praisal of outcomes of past patients. There

be causally associated with executed or

is a need to use predetermined criteria

avoided prosthodontic therapy (Table 6:3).

that are recognized as relevant through-

Individually, the incidence of out-

out follow-up observation period. These

comes as reported in the literature can

criteria need to be objective enough to

provide a content restricted relatively

describe precisely the results that are of

precise description of prognosis. Poten-

primary interest. An assessor of the pa-

Prognosis and Evidence Based Prosthodontics

tient may introduce a subjective dimension if he or she knows about the previous

data or published clinical study data. In the analysis of published data, two

patient history or if it is the same person

strategies can be applied to the problem.

who has undertaken a clinical interven-

The first is a simple variant of a “what

tion. If an intervention has been provided

if…” approach, or so-called sensitivity

to patients the assessor of the outcomes

analysis. Imagine that the prognosis of

should preferably not know the type or

100 prostheses were to be estimated over

extent of the therapy, i.e., attempts should

5 years in a prospective study. Let’s say 10

be made to have a blinded assessor. From

prostheses fractured over this period. At

a methodological perspective, it is also

the same time, 25 patients with the same

preferable that even the patient and the

number of prostheses withdrew for vari-

provider are blinded although this is evi-

ous reasons. A number of “success” can

dently difficult in prosthodontics care.

be calculated as 100% -10/75 = 87%. How

Time factor

can one account for the prostheses in the 25 patients that withdrew? Maybe some

Events following prosthetic therapy gen-

of these also fractured? In a “worst-case”

erally take a long time to develop and it is

scenario all would have fractured, which

understandable that each patient cannot

will give a “success” of 100%- 35/100 =

be followed up until some biological or

65%. Reciprocally, in a best-case scenario

technical problem develops. One main

none would have fractured and provide

question is what should be considered as

an estimate of “success” of 100%- 10/100

a relevant follow up time. Short observa-

= 90%. The large difference between 65%

tion periods do not provide especially

and 90% after the sensitivity analysis

meaningful information to present to our

indicates perhaps that the proportion

patients. With a long observation period

of withdrawals in this study was too

follows often the problem that patients

high to make any meaningful conclu-

disappear. It is important to establish

sions. The other possibility is to apply

the reasons for such withdrawals. Some

the so-called 5-20-rule of thumb. This

reasons for withdrawal, such as change

rule is interpreted such that less than

of address, death and incapacitation are

5% withdrawal can be ignored, while

inevitable and usually independent of

more than 20% withdrawal reduces the

prognosis. We don’t have to worry too

validity of the study. These percentages

much about these withdrawals, especially

are of course only indicative and must

if the rates are trivial. Other reasons can

be evaluated in relation to the incidence

be age or medical condition, or desire

of technical and clinical problems.

to no longer be recalled. If the latter

Since the incidence of adverse events

group is large, the validity of any conclu-

in prosthodontic therapy is relatively

sions becomes reduced – regardless of

low, it is difficult from a methodological

whether this is based on own practice

perspective to estimate prognosis from

Prognosis and Evidence Based Prosthodontics

studies with high patient withdrawals.

ning treatment for the individual patient. Unfortunately, relative risks or odds

Quantitative (Whatâ&#x20AC;&#x2122;s the probability that certain events will develop?)

ratios are somewhat vague constructs

A discussion about incidence of lack of

incidences of biological and technical

quality requires different approaches

failures can be established and reported

for addressing technical defects on one

for certain time intervals, e.g. after 1 year

hand, and biological effects on the other.

or 5 years. More common in prosthodon-

Technical defects are a component of

tics is to report time-to-event of various

the estimation of prognosis that is dir-

outcomes. Two common measures in this

ectly related to the prosthodontic part

category are median-time and survival

of the therapy, and is directly related to

estimates. Median time is defined as

the quality of the technological process,

when the time-to-event of interest has

including material qualities. For the

developed in 50% of the statistical units.

biological parameters there is no simi-

The statistical unit can be defined either

lar direct relationship. In this case, the

as the patient, the jaw or the prosthesis.

prognosis will often primarily be depend-

Survival curves indicate estimates for any

ent of the underlying disease and only

given time of the percentage of statistical

dependent of the prosthodontic therapy

unit that is defined as intact according to

to such degree that it per se predisposes

a specified criterion. Several events can be

for disease progression or affects the

described, e.g., degrees of successive devi-

danger of recurrence. Meaningful infor-

ations from perfect function or aesthetics,

mation to the patient about biological

secondary caries or endodontic complica-

prognosis must therefore include a com-

tions of abutment teeth, fractures, oral

parative element where the relevance

candidiasis, etc. Survival curves provide

of the original diagnosis is emphasized

the most information since the curve

and where the role of the prostheses as

shape will indicate whether the prognosis

a prognostic factor is contextualized.

is constant throughout the observation

Several investigators have presented

for quantifying how the clinical performance of prostheses will be affected. The

period, alternatively improve or worsen

the relative and absolute risks, alterna-

over various time spans (Figure 6:1).

tively as odds ratios for such events to

Figure 6:1

develop as functions of, e.g., patient de-

have been identified as predicting treat-

Observation viewpoint (Therapy defined disease versus patient experienced illness?)

ment success, which needs to be taken in

The criteria for success or failure of pros-

consideration when diagnosing and plan-

thodontic interventions can vary de-

mographics, modifications of prosthesis design, prior dissatisfaction with prosthesis, etc. Thus, specific prognostic factors

Prognosis and Evidence Based Prosthodontics

% 100

50 0

Years

Figure 6:1. Examples of three differently shaped survival curves over 20 years. The vertical bars indicate the confidence interval (C.I.) of the estimates, usually the 95% C.I. The red curve indicates a survival estimate that is linear over time and does not vary, but with a wide C.I. The green curve (with a narrow C.I.) shows a good survival until about 15 years followed by a marked drop in survival estimates. The blue curve suggests a relatively rapid drop in survival estimate, but after 5 years the survival estimate remains relatively stable, and in this constructed example it demonstrates the best survival after 20 years. If the C.I. bars do not overlap on the graph, one may deduce that there is a statistically significant difference between the survival curves. Please note that the vertical axis for illustrative purposes stops at 50% in this example, while some journals require a scale beteen 0 and 100%.

pending on the observation viewpoint.

symptoms may appear as uninterest-

Operator defined criteria can markedly

ing, while details related to the experi-

deviate from the criteria that patients

ence of the prosthesis as a foreign object

value. Moreover, the patient expecta-

and deviation from expected aesthetic

tions may vary greatly within these main

achievements are highly relevant.

groups. In general, the operator will re-

The patientâ&#x20AC;&#x2122;s perception of the suc-

gard lack of defined disease conditions

cess of prosthodontic therapy is an

as important criteria in addition to the

important dimension. This outcome

technical characteristics of the prosthetic

causes interpretative problems when we

device. From the patientâ&#x20AC;&#x2122;s perspective,

evaluate the success or failure of prostho-

however, sometimes modest biological

dontic therapy. One term that is often

Prognosis and Evidence Based Prosthodontics

used is “oral discomfort”, acknowledg-

prognoses to patients becomes very in-

ing that this state is strongly influenced

accurate. If one is to base opinions on

by individual predispositions as well as

prognosis from the literature there is

considered in a cultural context. Several

general consensus that case reports about

papers with focus on the effects of loss of

treatment results have a limited value.

tooth on patients’ quality of life report

Indeed, the term anecdotal value is used

findings ranging from a description of a

for such reports. On the other hand, one

near suicidal state to an almost complete

may argue that even randomized well

lack of any outward indication of loss

controlled trials of large populations also

explained by a societal conditioning.

have limited value when the results are

Both the clinician and the patient

to be applied on an individual level. The

have opinions on what is most import-

reason is that patients who consent to

ant. Different emphasis can be placed on

extensive follow-up studies are probably

the quality of the remaining dentition,

not representative of the average patient.

to what extent stomatognathic functions

Preferably, all dentists should have

may be restored or maintained and to

systematized their own documenta-

what extent patient defined criteria are

tion of prognosis based on accrued data

acceptable, for example as relates to aes-

following prosthodontic treatments.

thetics, function and comfort. Finally,

Unfortunately, this is seldom the case,

there may also be discrepancy of opinions

perhaps except for implant based pros-

as regards different criteria to describe the

theses. Most dentists therefore base their

qualities of the prosthesis and relevance

estimates on reported data from the

for describing or evaluating the prognosis.

literature. There is no principal differ-

All in all, it is debatable what the most

ence between critically appraising one´s

relevant outcome is when we evaluate

personal empirical data generated in

the prognosis of prosthodontic therapy.

own practice differently from evaluating

Documentation estimations on prognosis (aggregated data from published studies of populations versus the individual clinician and patient?)

the data in published clinical studies. For both information sources, the same requirements apply regarding validity, outcomes and usability of the information applicable to prognosis. Firstly, it is important to appraise whether the data applied as basis for estimating prognosis

The ideal situation is that a systematic

are valid. Threats to validity are patient

documentation of experiences in own

withdrawal rates and a clarification of

clinical practice should provide a foun-

the reasons for patient disappearing

dation for opinion about prognosis of

or withdrawing from clinical trials.

prosthodontic therapy. The moment that this is not systematized conveying

A published study claiming that specific subpopulations may have different

Prognosis and Evidence Based Prosthodontics

prognoses must be appraised specifically

program. Perhaps this, in the end, is the

for several aspects: First one must estab-

most likely factor that determines suc-

lish whether all important prognostic

cess of removable prosthodontics care.

factors were considered. In other words, we expect that the authors have con-

Treatment planning

sidered whether or not other important

In daily clinical practice, published data

subgroup predictors have influenced

may be of interest, but only if they can

the treatment outcome. E.g., in a study

be directly applied to specific treatment

claiming that elderly patients with xe-

decisions. In this perspective, it is im-

rostomia have a worse prognosis regard-

portant to be conscious about several

ing prosthesis function than younger

elements relative to clinical studies:

patients, a central question is whether There are both easy solutions to adjust

The operator and patient factor

for potential interactions between these

Several reservations must be made before

predictors or more advanced methods,

we may translate numerical findings in

that are either stratified cross-tabulations

the literature regarding prognoses within

or multiple regressions. In both cases we

prosthodontics: first of all, the operator in

must evaluate the materials and meth-

most of the core studies is often specially

ods section to appraise whether this has

selected and trained. Studies are often

been attempted, before we proceed to ac-

carried out by experienced clinicians

cept the author’s eventual conclusions.

within special institutions such as dental

Discussing prognosis by using the

faculties, competency centers or specialist

age or xerostomia is the critical factor?

terms “success”, “survival”, “complica-

clinics. There are reasons to believe that

tion” and “failure” is fraught with risks

both the selection of patients, choice of

of misunderstandings, both in reporting,

treatment, control of technical quality

reading, interpretation, and patient

and maintenance and follow-up routines

communication. There is no universally

deviate markedly from the conditions

agreed taxonomy, and this should be re-

that exists for the patient or patient group

membered when we explain to patients

we encounter in our own practices. It may

the potential risks of adverse events as-

be tempting to state that the numbers

sociated with removable prosthodontics

we operate with when informing about

therapies. Moreover, it should also be

prognoses are overestimations of treat-

borne in mind that the most likely rea-

ment success. These study data reflect to a

sons for failure of partially removable

large extent the potentials of the different

prostheses, i.e., caries and periodontitis,

prosthodontic therapies under optimal

and for removable, i.e., loss of retention,

conditions, rather than the predictive

can be counteracted by maintaining an

outcomes for the average patient in real

individually adapted patient supportive

life practical dentistry. Two terms are be-

Prognosis and Evidence Based Prosthodontics

ing used in the literature to denote the

dibular dysfunction, rheumatoid arthritis,

difference in interpretation of such study

situation in antagonistic jaw, bruxism,

results: Efficacy describes the potential of

positional instability of the remaining

an intervention under optimal conditions

dentition, routine follow-up controls ver-

while effectiveness is a description of the

sus sporadic controls, etc. Known biologi-

results under realistic settings amongst

cal/technical factors that may affect the

a population of non-selected clinicians.

prognosis for removable prosthodontics

Correct identification of the patientâ&#x20AC;&#x2122;s problems

are alloy, prosthesis extension, dimensioning and abutment vitality, marginal periodontitis, patient hygiene, etc. for cast

It is always presumed that the dentist

partial removable dental prostheses. For

makes a correct and complete diagnosis.

complete removable dental prostheses the

How often is this true when remov-

prognosis is dependent on the patientâ&#x20AC;&#x2122;s

able prosthodontic therapy is planned?

ability to accommodate to a new situ-

Diagnosis of both the operator-defined

ation, jaw morphology, extent of bone

disease as well as the patient experienced

resorption, osteoporosis, xerostomia,

illness will indicate the most appropriate

etc. For implant-retained prostheses ad-

choice of therapy and thereby guide the

ditional factors are also relevant, such as

objectives of the therapy significantly.

smoking, bone quality and dimensions,

It would seem evident that population

implant material and -dimensions, etc.

based prognosis-estimates based on a

For all therapies, the level of prosthodon-

purely morphological diagnosis criter-

tic competency as well as competency

ion such as, e.g. lost maxillary incisor,

of the dental technician will have an

have a limited translation value to single

effect on prognosis, and for the latter

patients with different basis diagnoses

therapeutic approach it will also depend

such as agenesis or juvenile periodontitis.

on the competency of the oral surgeon.

Too often, the prosthodontic diagnosis observations of remaining dentition

How should we explain prognosis to our patients?

or periodontal support and short term

One must not forget that we all have dif-

result of eventual preprosthetic causal

ferent attitudes to risk and risk evalua-

therapy against caries and periodontitis.

tion. What seems rational to one person

is indeed limited only to morphological

For all categories of prosthodontic

may be considered precarious by some

therapy there are specific subgroups of

and unproblematic by others. Our obliga-

patients that will have a divergent prog-

tion as doctors is therefore to present to

nosis apart from the general population.

our patient in the most objective manner

The prognosis for all forms of prostho-

available knowledge and data relative to

dontic therapies can be associated with

the prognoses of alternative prosthodon-

any or is cumulative in presence of man-

tic therapies, including none, as a basis

Prognosis and Evidence Based Prosthodontics

for our patients’ selection of what they

we “guarantee” longevity and/or treat-

consider the most appropriate alterna-

ment success. Unrelated to our knowledge

tive from their holistic perspective.

about prognosis, it is our professional ob-

We all wish to satisfy our patients by

ligation to point out that the predictabil-

providing prosthodontic solutions with

ity of an “average prognosis” is dependent

a precise description of how long it will

on specific main criteria (e.g. such that

last. Unfortunately, this is not possible.

the prostheses not necessarily MUST be

All numbers from studies are based on

removed due to adverse biological dam-

averages, which mean that for some pa-

age), that an average of 10 years can mean

tients, the prosthesis will function for a

that both 3 or 18 years are “normal”, and

very long time, while in others for a very

finally that technical success and a proper

short time. Our discussions with the pa-

oral hygiene regime does not guarantee,

tient must reflect this fact and not lead

although it increases the chances, of suc-

us to infer to the patient or ourselves that

cessful prosthodontic therapy outcomes.

Further reading Bergman B. Prognosis for prosthodontic treatment of partially edentulous patients. In: Prosthodontics. Principles and management strategies. Öwall B, Käyser AF, Carlsson GE (eds). London: Mosby-Wolfe, 1996, 149-160. Celebic´ A, Knezovic´-Zlataric´ D. A comparison of patient’s satisfaction between complete and partial removable denture wearers. J Dent 2003; 31: 445-451. Creugers NH, Kreulen CM. Evidence for changes in removable partial and complete denture treatment and biologic compatibility. Int J Prosthodont 2003; 16 Suppl: 58-60. De Boever JA, Carlsson GE, Klineberg IJ. Need for occlusal therapy and prosthodontic treatment in the management of temporomandibular disorders. Part II: Tooth loss and prosthodontic treatment. J Oral Rehabil 2000; 27:647-659. Gotfredsen K, Walls AW. What dentition assures oral function? Clin Oral Implants Res 2007;18 Suppl 3: 34-45. Grundström L, Nilner K, Palmqvist S. An 8-year follow-up of removable partial denture treatment performed by the Public Dental Health Service in a Swedish county. Swed Dent J 2001; 25: 75-79. Jokstad A, Bayne S, Blunck U, Tyas M, Wilson N. Quality of dental restorations. FDI Commission Project 2-95. Int Dent J 2001; 51: 117-158. N’gom PI, Woda A. Influence of impaired mastication on nutrition. J Prosthet Dent 2002; 87: 667-673. Öwall B, Budtz-Jørgensen E, Davenport J, Mushimoto E, Palmqvist S, Renner R, Sofou A, Wöstmann B. Removable partial denture design: a need to focus on hygienic principles? Int J Prosthodont 2002; 15: 371-378.

Prognosis and Evidence Based Prosthodontics

Palmqvist S, Carlsson GE, Öwall B. The combination syndrome: a literature review. J Prosthet Dent 2003; 90: 270-275. Strassburger C, Kerschbaum T, Heydecke G. Influence of implant and conventional prostheses on satisfaction and quality of life: A literature review. Part 2: Qualitative analysis and evaluation of the studies. Int J Prosthodont 2006; 19: 339-348. Wöstmann B, Budtz-Jørgensen E, Jepson N, Mushimoto E, Palmqvist S, Sofou A, Öwall B. Indications for removable partial dentures: a literature review. Int J Prosthodont 2005; 18: 139-145. Zlatarić DK, Celebić A. Treatment outcomes with removable partial dentures: a comparison between patient and prosthodontist assessments. Int J Prosthodont 2001; 14: 423-426.

Prognosis and Evidence Based Prosthodontics View publication stats

AN INVITED EDITORIAL

Evidence-based prosthodontics: 25 years later This editorial relates the events and behind-the-scenes vision and activity of the many prosthodontists and prosthodontic organizations that brought evidencebased dentistry (EBD) to our specialty. In 1986, Jim Anderson, a prosthodontist at the University of Toronto, was granted a sabbatical year to study clinical epidemiology at McMaster University Medical School in Hamilton, Ontario, Canada. The professor was David Sackett, a nephrologist and epidemiologist who, in 1967 and at the age of 32, had been awarded the department chair. He combined his skills in epidemiology and biostatistics into a method not only of evaluating and appraising the quality and validity of scientific literature but also of clinical action. He has been given the title, “Father of Evidence-based Medicine,” a term coined by one of his students, and his department grew to such numbers that it was described as “the department that ate a medical school.” Even in 2017, it is the largest medical school department in Canada. In 1995, Sackett repeated a 5-year hospital residency because, although he was a professor, he felt he was not a very good doctor. He personally confirmed what he had been teaching his medical colleagues for years: valid, up-to-date (via immediate computer search), patientcentered treatments can be delivered even in a busy hospital ward. After his sabbatical, Jim Anderson returned to Toronto to be the first to bring the McMaster model of clinical epidemiology to dentistry. In 1989, the Federation of Prosthodontic Organizations sponsored a national symposium held at the Mayo Clinic, Rochester, Minnesota to address current and future aspects of prosthodontic education, research, and education for the 21st century. The section report on research was chaired by George Zarb, who laid the groundwork for implementing Jim Anderson’s Toronto educational initiative. A research symposium committee was organized with representatives from many prosthodontic organizations and academic institutions under the leadership of Dale Smith and populated by George Zarb, Cosmo Desteno, Steve Bergen, Jack Gerrow, Robert

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Schweitzer, and Jim Anderson. Discussions ended in negotiations with McMasters University and the esteemed Sackett faculty and the creation of a specially designed program to educate 10 prosthodontists in the understanding and teaching methods of evidence-based medicine. In turn, these 10 would bring their newly acquired skills to prosthodontic program directors and educators in North America. The stage was set for McMaster University Department of Epidemiology and Biostatistics to change its diet and to “eat the dental specialty of prosthodontics.” In 1993, the 10 attendees were deﬁned as those with a strong relationship to the major prosthodontic journals: The International Journal of Prosthodontics, The Journal of Prosthetic Dentistry, Journal of Prosthodontics, and International Journal of Oral and Maxillofacial Implants. The 10 individuals were George Zarb, Jim Anderson, David Felton, Gary Goldstein, Jack Preston, Patrick Lloyd, Rhonda Jacob, Alan Carr, Glen McGivney, and Brien Lang (Fig. 1). In 1993 and 1994, the group of 10 traveled to McMasters and attended two 1-week courses with

Figure 1. Evidence-based dentistry workshop attendees at McMaster’s University. Back row (left-to-right): Gary R. Goldstein, David A. Felton, James D. Anderson, Jack D. Preston, and Brien R. Lang. Front row (left-toright): Alan B. Carr, Glen P. McGivney, Rhonda F. Jacob, George A. Zarb, and Patrick M. Lloyd. (Photograph from J Prosthet Dent 2001;85:525-6.)

small-group, self-directed, problem-based learning/teaching methods pioneered by the McMaster group. Faculty were from the medical school and included George Browman, Gordon Guyatt, Mark Levine, and Ray Gilbert. In the first week, the Workshop on How to Teach the Critical Appraisal of Clinical Evidence covered 8 units: Therapy, Diagnostic Test, Overview, Clinical Measurement, Prognosis, Causation, Quality of Care, and Economic Evaluation. In the second week, the Research Methods Workshop reviewed the knowledge base required to prepare a research protocol. Topics included establishing the research question, selecting design architecture appropriate for the question, sample selection, and size, and describing the maneuver, measurement, outcomes, and statistical analysis. The goal was for the group of 10 to disseminate their synthesis of the experience working with the McMaster faculty in preparing dental examples and teaching modules to the prosthodontic community. In 1994, an editorial written by George Zarb and echoing the sentiment of his colleagues was published simultaneously in all 4 journals represented by the attendees. Zarb’s editorial elegantly described the state of our “treatment dilemmas” due to lack of clinical evidence to support one treatment decision over another. In this editorial and in a subsequent 1995 announcement for upcoming International EBD symposia, he recognized the support that carried the EBD mission forward, crediting the Federation of Prosthodontic Organizations and the Editorial Council of The Journal of Prosthetic Dentistry (ECJPD). The Editorial Council under Ken Adisman pledged significant financial support from the outset of the initiative. In 1995 and 1997, the original group of 10 assisted by George Browman, held 2 international research symposia sponsored by the American College of Prosthodontics and the ECJPD. The target audience was prosthodontic educators, who were given the tools to begin teaching their students the concept of EBD. The curricula included critical appraisal exercises directed at core clinical decisions related to diagnosis, harm, therapy, prognosis, and systematic review. Discussion of research design and measurement issues was directed at various clinical research questions of interest. The attendees were encouraged to become involved with the Cochrane Collaboration research activities established in 1993 by David Sackett, who was the first chair of the Cochrane Steering Group. In 1997, several other dental specialties and dental educators attended the symposia, having observed the expertise that was being introduced to the dental community by this prosthodontic initiative. In 2000, in the first 7 issues The Journal of Prosthetic Dentistry published a series of 8 articles written by the 10 attendees and associates to be used as guides to understanding and appraising the validity of clinical research and its applicability to the patient in question. The first 2 THE JOURNAL OF PROSTHETIC DENTISTRY

Volume 119 Issue 1

articles described the concept of EBD.1,2 The next 2 provided information regarding study design and measurement issues that are helpful for determining the strength of evidence and the quality of outcomes.3,4 These articles were followed by core evidence-based articles designed to help readers determine the validity and usefulness of publications to assist clinical decisionmaking. These core articles were categorized as diagnosis,5 prognosis (probable course of a disease),6 harm7 (observational studies of exposures that may cause harm), and therapy8 (whether a specific treatment is better than another course of action). Also presented was the systematic review, which is a structured review format that uses explicit methodology for conducting rigorous reviews of the literature. In 2002, Gary Goldstein was the guest editor and author of, “Evidence-based dentistry” in Dental Clinics of North America. Several of his prosthodontic colleagues and others in the epidemiology specialty were authors in the edition. In 2009, another Dental Clinics of North America called, “Evidence-based dentistry in the private office,” was held, and in 2017, “The science and art of evidence-based pediatric dentistry,” was published in Dental Clinics of North America. From 1999 to 2002, the Academy of Prosthodontics allotted one half day of its annual scientific sessions to the concepts of EBD. The half-day included guest speakers and break-out sessions implementing EBD in reviewing various clinical questions and available literature. Academy fellows Alan Carr, Rhonda Jacob, Sree Koka, and Steven Eckert were the planning committee and facilitators for the sessions. The American Dental Association Center for Evidence-Based Dentistry was established in 2007, and the Journal of Evidence-Based Dental Practice was first published in 2002. Many dental schools and dental organizations have implemented EBD in their curricula. Problem/patient/ population, intervention/indicator, comparison, outcome (PICO) questions and critical appraisal topics drive literature searches in the clinic and in seminars. The commitment of prosthodontics to the implementation of evidence-based decision-making is demonstrated by the fact that EBD education is now a prosthodontic standard for all dental schools in the United States according to the Commission on Dental Accreditation. Educated audiences demand more quality of research design and validity of assessment of outcomes from speakers at scientific sessions. The concepts of evidence-based medicine can be applied across all health disciplines and also further afield. For example, Evidence-Aid (www.evidenceaid. org) was established after the Indian Ocean tsunami in 2004 with input from Cochrane to collate and use knowledge from systematic reviews to “inform agencies and people planning for, or responding to, disasters” in the humanitarian sector. Regardless of the application, Jacob et al

January 2018

health or humanitarian, identifying interventions that are known to be beneficial, are known to be harmful, or have outcomes which are not yet well understood relies upon being able to find and understand the evidence. In dentistry, collation of evidence is often challenged by the length of time it can take for outcomes to become apparent. This makes it difficult to design and fund investigative studies and to track patients forward in time. However, it must be remembered that EBD means that clinical prosthodontists seek the most appropriate evidence and assess it in light of their own abilities and their patients’ wishes, even if that evidence is not considered to be of the highest quality. The technology boom has assisted in the identification of appropriate evidence and has facilitated EBD. The MEDical Literature Analysis and Retrieval System (MEDLARS) Online replaced the manual Index Medicus system in 1971, with MEDLINE launched free to the general usership via PubMed in 1997. Other bibliographic databases and search engines across many languages are now either freely available or accessible through library subscriptions. EBD development paralleled technological changes as we moved from desktop computers to laptops, with evidence now available on portable tablets in every office. Barriers to accessing information and evidence are ever decreasing, and quality syntheses and guidelines for applying that evidence are ever increasing. The evidence tree has also evolved, helping clinicians access and translate evidence into their practice. Most clinicians know the evidence tree as having case reports and expert opinion at the bottom of a pyramid which then culminates with systematic reviews at the top. The 6-S hierarchy of evidence-based resources model was introduced in 2009 acknowledging the expansion of evidence beyond that of systematic reviews.9 Single studies continue to form the first layer, but above systematic reviews (now called syntheses), synopses and systems have been added. Synopses are critical appraisals of studies or reviews written by epidemiology experts and available through resources such as TRIP database (www.tripdatabase.com.au) and Evidence-Based Dentistry (www.nature.com/ebd/), so that practicing clinicians can access appraised evidence in a meaningful and timely manner. Finally, in some areas, clinical system guidelines have been developed, and this is now considered to be the highest evidentiary layer. Although evidence in prosthodontics is not yet sufficiently mature to offer system guidelines, we have good access to synopses and continue to work with and improve our evidence base. We recognize that different evidence is needed to answer different prosthodontic questions and that different study designs are more

Jacob et al

appropriate for the exploration of different prosthodontic outcomes; for example, patient-centered outcomes with cross-sectional surveys, lifespans of implant prostheses with cohort studies, or dental material choice with randomized clinical trials. Clinically, when providing prosthodontic treatment, we almost always make and guide daily decisions by weighing the costs of treatment against potential beneﬁts. To do so, we must assess evidence from a variety of resources. Approximately 25 years have passed since evidencebased prosthodontics became the headliner for prosthodontic annual sessions, symposia, study clubs, and resident seminars. Like the introduction of root-form dental implants in North America, it also grew under the leadership of our prosthodontic colleagues at the University of Toronto: a select few understood the potential, those few became trained, and they then became the trainers. A whole generation of prosthodontists may not even recognize that implant and evidence-based prosthodontics are being taught to them by senior staff that learned by traveling to seminars, performing on the job, and then developing curricula for their own schools and practices. Rhonda F. Jacob, DDS MS Private practice and Retired Professor, MD Anderson Cancer Center, The Woodlands, Texas. Gary R. Goldstein, DDS Professor, Department of Prosthodontics, New York University College of Dentistry, New York, NY. Danielle M. Layton, BDSc(Hon)(Qld), MDSc(Hons)(Syd), MSc Oxon, DPhil Oxon Private practice and Adjunct Associate Professor, University of Queensland, St. Lucia, Queensland, Australia.

REFERENCES 1. Anderson JD. Need for evidence-based practice in prosthodontics. J Prosthet Dent 2000;83:58-65. 2. Carr AB, McGivney GP. Users’ guides to the dental literature. How to get started. J Prosthet Dent 2000;83:13-20. 3. Jacob RF, Carr AB. Hierarchy of research design used to categorize the “strength of evidence” in answering clinical dental questions. J Prosthet Dent 2000;83: 137-52. 4. Carr AB, McGivney GP. Measurement in dentistry. J Prosthet Dent 2000;83: 266-71. 5. Eckert SE, Goldstein GR, Koka S. How to evaluate a diagnostic test. J Prosthet Dent 2000;83:386-91. 6. Zarb GA, Anderson JD. Evidence-based dentistry: prognosis. J Prosthet Dent 2000;83:495-500. 7. Goldstein GR, Preston JD. How to evaluate an article about therapy. J Prosthet Dent 2000;83:599-603. 8. Jacob RF, Lloyd PM. How to evaluate a dental article about harm. J Prosthet Dent 2000;84:8-16. 9. DiCenso A, Bayley L, Haynes R. Accessing preappraised evidence: ﬁne-tuning the 5s model into a 6s model. Ann Intern Med 2009;151:JC3-2-3. Copyright © 2017 by the Editorial Council for The Journal of Prosthetic Dentistry.

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Evidence-based considerations for removable prosthodontic and dental implant occlusion: A literature review Thomas D. Taylor, DDS, MSD,a Jonathan Wiens, DDS, MSD,b and Alan Carr, DDS, MSc University of Connecticut, School of Dental Medicine, Farmington, Conn; University of Detroit Mercy, Detroit, Mich; Mayo College of Medicine, Rochester, Minn The dental literature is filled with discussions of dental occlusion, occlusal schemes, philosophies, and methods to correct and restore the diseased, worn, or damaged occlusion. Traditionally, these discussions have been empirical in nature and not based on scientific evidence. Due to the empirical nature of the literature, the study of occlusion has been extremely complex and troublesome to both pre- and post-doctoral students. The introduction of osseointegrated implants has further complicated the situation. Dentists may apply the principles of occlusion for the natural dentition directly to implant-supported and retained restorations. Although this may be successful, this rationale may result in overly complex or simplified treatment protocols and outcomes. There is an emerging body of scientific literature related to dental implant therapy that may be useful in formulating treatment protocols and prosthesis designs for implant-supported restorations. This review focuses on some of the ‘‘classic’’ removable prosthodontic literature and the currently available scientific literature involving removable prosthodontic occlusion and dental implant occlusion. The authors reviewed the English peer-reviewed literature prior to 1996 in as comprehensive manner as possible, and material after 1996 was reviewed electronically using MEDLINE. Electronic searches of the literature were performed in MEDLINE using key words—animal studies, case series, clinical trials, cohort studies, complete denture occlusion, dental implant function, dental implant occlusion, dental implant occlusion research, dental implant functional loading, dental implants, dental occlusion, dental occlusion research, denture function, denture occlusion, dentures, implant function, implant functional loading, implant occlusion, occlusion, and removable partial denture occlusion—in various combinations to obtain potential references for review. A total of 5447 English language titles were obtained, many of which were duplicates due to multiple searches. Manual hand searching of the MEDLINE reference list was performed to identify any articles missed in the original search. (J Prosthet Dent 2005;94:555-60.)

he study of human occlusion has a broad and fascinating history in the dental literature. The literature, while extensive, is largely empirical in nature and based on theory and anecdote with little scientific basis. In spite of this potential shortcoming, most occlusionrelated dental therapy may be deemed successful if it is assumed that results such as patient comfort, satisfaction, and restoration durability are acceptable outcomes. The introduction of osseointegrated dental implants has dramatically altered the scope of prosthodontic treatment. The availability of predictable, stable anchorage for prosthetic tooth replacement has expanded treatment options but has also increased treatment planning and technical complexity. The extrapolation of occlusal concepts from natural teeth to dental implants has been an unavoidable progression simply because no

Presented at the Academy of Prosthodontics 86th Annual Scientific Session, Niagara Falls, Ontario, Canada, May, 2004. a Professor, Department Head, Department of Oral Rehabilitation, Biomaterials and Skeletal Development, University of Connecticut, School of Dental Medicine. b Clinical Professor, University of Detroit Mercy. c Professor, Department of Dental Specialties, Mayo College of Medicine.

DECEMBER 2005

alternative, scientific, or empirical theory has been put forward. In short, occlusion for dental implantsupported or retained restorations has largely been an extension of natural tooth occlusion and/or complete denture occlusion with a few twists.1 This literature review was undertaken in an attempt to clarify current understanding of the scientific basis for removable prosthodontic occlusion, dental implant occlusion, and the occlusal concepts and methods currently advocated for both. A review of the dental literature concerning occlusion was undertaken. Material appearing in the literature prior to 1996 was reviewed in as comprehensive manner as possible, and material after 1996 was reviewed electronically. Electronic searches of the literature were performed in MEDLINE using key words—animal studies, case series, clinical trials, cohort studies, complete denture occlusion, dental implant function, dental implant occlusion, dental implant occlusion research, dental implant functional loading, dental implants, dental occlusion, dental occlusion research, denture function, denture occlusion, dentures, implant function, implant functional loading, implant occlusion, occlusion, and removable partial denture occlusion—in various combinations to obtain potential references for review. A total THE JOURNAL OF PROSTHETIC DENTISTRY 555

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TAYLOR, WIENS, AND CARR

Fig. 1. Hanau’s Quint. (From Hanau RL. Articulation defined, analyzed and formulated. J Am Dent Assoc 1926;13:1694-709. Copyright 1926 American Dental Association. All rights reserved. Reproduced by permission.)

of 5447 English language titles were obtained, many of which were duplicates due to multiple searches. The titles were reviewed and selected for closer examination if it appeared that the article was a study of any type. Manual hand searching of the MEDLINE reference list was performed to identify any articles missed in the original search. As the vast majority of articles reviewed were descriptive in nature, and because of the very limited number of human clinical trials found, it was decided to report findings in a descriptive manner rather than as a systematic review of the available clinical trials identified. This permitted the inclusion of in vitro and in vivo studies including nonhuman studies. Articles were included if they were thought to provide experimentally derived, objective information regarding occlusion. Completely empirical or anecdotal articles were excluded except in those instances when they were of ‘‘classic’’ value in describing philosophy and/ or technique. Those ‘‘classic’’ articles are limited to the discussion of removable prosthodontic occlusion.

Removable prosthodontic occlusion Modern theories and concepts of occlusion for implants and natural teeth have originated in complete denture construction. The Pankey-Mann concept of 556

occlusal rehabilitation takes its origins partially from the Monson spherical theory of occlusion as it was originally conceived for complete denture construction.2 The early gnathological approach to occlusal rehabilitation evolved from the concept of balanced articulation, which can be defined as bilateral, simultaneous, anterior and posterior occlusal contact of the teeth in centric and eccentric positions.3 Bilateral articulation, or balance, as the occlusal scheme of choice has a long history in complete denture construction.4 It was believed that gliding tooth contacts in harmony with the anatomical condylar guidance and incisal guidance established to achieve esthetic and phonetic goals was most appropriate to lessen denture base instability, as well as residual ridge atrophy and possible deleterious effects of parafunctional habits. Attempts to develop a scientific basis for clinical observations and an effort to create a balanced occlusion led to geometric schemes and engineering or mathematical models (Fig. 1).5 As a result, numerous articulators were developed to mechanically record and replicate maxillomandibular relationships, along with a variety of tooth forms to correspond to the balanced occlusal scheme theory and their prescribed formulation. The principles of balanced occlusion required the recording of the VOLUME 94 NUMBER 6

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patient’s condylar guidance and the establishment of the incisal guidance as predicated by esthetic and phonetic determinants, skeletal relationships, and acceptable vertical dimension of occlusion. Posterior cusp form, plane of occlusion, compensating curve and/or tooth selection became products of the end determinants. Modification in the tooth arrangement by the incorporation of a compensating curve or alteration in the plane of occlusion/orientation was further subscribed to achieve the simultaneous or bilateral occlusal tooth contact. The authors believe that the perceived confusion associated with the term ‘‘balanced occlusion’’ led to multiple interpretations in different geographical areas and at different times, making standardization nearly impossible. It should be considered that the presence of a food bolus could negate the simultaneous bilateral tooth contacts deemed so desirable6; however, others contended that penetration of the food bolus results in desirable tooth contacts.7-13 In 1972, a workshop was conducted on the subject of complete denture occlusion.14 Eighty-nine participants met to examine the current state of knowledge of the scientific basis for complete denture occlusion. In the summary of the chapter on occlusal patterns and tooth arrangements, Kapur disassociated occlusion from denture efficiency.15 A review of publications comparing various occlusal forms, materials, and occlusal arrangements, including studies since 1972, confirms Kapur’s observation that there is no scientific evidence supporting the use of one occlusal form or arrangement over another.16-38 The quandary that clinicians find themselves in when searching for a scientific basis for the best technique, material, tooth design, or occlusal scheme in removable prosthodontics may be best understood by examining the literature and observing the apparent clinical success of diverse empirical methods. It is evident that there are multiple pathways to clinical success when considering occlusal concepts for removable prosthodontics. Jacob39 noted that although the earlier observations and techniques were scientifically unproven, they remain in clinical practice today essentially unchanged as accepted parameters of care.

The effect of nonaxial load on implant function and survival Relative to implant-supported prostheses, numerous authors have stated the need to avoid the application of nonaxial forces to dental implants whenever possible.40-45 The reasons cited for this concern focus primarily on the absence of a periodontal ligament supporting the implants and the observation that nonaxial forces will create areas of high stress concentration instead of uniform compression along the implant to bone interface. The nonaxial loading of a mechanical device assembled with screw joints, such as dental implants, puts DECEMBER 2005

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those components at greater risk of failure through fatigue and/or recurrent loosening of screws. The mechanical failures, primarily from clinical experience but also from in vitro and animal studies, appear to be valid.42,46,47 Evidence is lacking, however, regarding the effect of nonaxial load (or overload) on the integrity of the osseointegrated interface between bone and implant. The shape and surface texture of cylindrical, endosseous implants make it impossible for a vertically applied load to be transmitted to the bone exclusively through compressive loading. A threaded profile, or even a rough surface on an implant, indicates that the load will be transferred to bone by compression in some areas, but also in tension and shear in other areas.48,49 By changing the direction of load application, the location and magnitude of compressive, tensile, and shear forces will be altered, but all 3 continue to participate in the transfer of load through the implant to surrounding bone. It should be recognized that the forces of occlusion are rarely vertical. Mastication is a side-to-side action that does not lend itself to axial loading of teeth or implants in the jaws. Similarly, the damaging effects of bruxism are created through lateral friction between the occlusal surfaces of maxilla and mandible. Thus, the resultant forces are not vertical. Two studies have specifically examined the effect of nonaxial loading on osseointegrated dental implants, one in a primate model with cyclical occlusal loading and the other in sheep with static loading.46,50 In both studies, the authors were unable to demonstrate a negative effect on bone-to-implant anchorage after extended periods of nonaxial loading. The limited evidence available does not demonstrate that nonaxial loading is detrimental to the osseointegrated interface between the bone and implant surface.

Progressive loading and occlusal overload of dental implants Numerous authors have written about the concept of progressive loading of dental implants.51-53 The concept may make intuitive sense when considering the role of Wolff’s Law in bone remodeling where bone mass will increase in response to stress.54 Gradually increasing the load applied to implants in poor quality bone, thereby allowing that bone to increase in mass and density through gradually increasing function, seems logical. The evidence available, however, does not support the need for progressive loading. Several studies have examined the effects of placing restorations on previously unloaded implants in heavier than normal occlusion.55-58 In these animal studies, restorations were placed on implants that had previously not been functionally loaded. In all situations, the occlusal overload generated at the time of abutment connection or initial functional loading was tolerated by the implants without evidence of deleterious effect. Loading previously unloaded 557

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implants by immediately subjecting the implant to extreme overload without negative effect does not support the principle of progressive loading. In a study by Isidor,58 fixed partial dentures secured to dental implants in ‘‘supra-occlusal contact’’ were followed from 9 to 15 months. When the natural teeth erupted back into occlusion, the prostheses were replaced (in some situations replaced twice) with prostheses that further increased the occlusal contact on the implant-supported restorations. This also generated a ‘‘lateral displacement’’ to the loading pattern of the implants. Unfortunately, the author failed to describe in a quantitative manner how much of a supra-occlusal contact was created or the magnitude of the lateral displacement. In this study, the original hypothesis of creating occlusal overload to cause implant failure was not successful, and only by further increasing the magnitude and changing the direction of the overload was an effect demonstrated. Although the second (or third) increase in occlusal overload on the implants did ultimately result in loss of some implants, the extent of additional increase in vertical dimension of occlusion created by the secondary increase in occlusal height does not necessarily reflect any comparable normal clinical situation and should be interpreted with caution. This is particularly true in light of the fact that the results of this study are not consistent with those published by others55-57,59,60 in which excessive occlusal load did not create adverse responses with implants. It may also be argued that the concept of progressive loading is, in fact, unlikely to be attained. In 1985, Skalak61 hypothesized that the selection of occlusal material would affect the survival of the underlying implant and its osseointegrated interface. Although the hypothesis was easily understood, it did not reflect normal masticatory function but, rather, was dependent on the assumption that occlusal movements involved impact type contacts between the arches. Several studies have examined the effect of occlusal material on load transfer to dental implants.62-64 The findings indicate that occlusal material does not affect the force transmitted through the prosthesis/implant to the surrounding bone, nor does prosthesis material affect the tissues adjacent to the implant(s). Similarly, there is no published evidence that modifications to the dimensions and occlusal contacts/anatomy of provisional restorations reduce loading of implant prostheses. The presence of parafunctional habits and mastication of food can generate high forces on implant-supported restorations, potentially negating prosthesis design aspects intended to reduce functional loads during the progressive loading period.65,66 The previously cited evidence does not support the contention that the osseointegrated interface may be damaged by full occlusal loading at the time the implant is brought into function.55-60 When coupled with the likelihood that performing a graduated 558

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loading protocol may be unlikely to be realized, the value of progressive loading as a treatment concept must be questioned. Similarly, the literature available at this time concerning occlusal overload in animal models does not reveal a direct cause-effect relationship between occlusal loading and implant failure (exclusive of implant fracture).55-60

Proprioception and dental implants The role of proprioceptive nerve endings in the periodontal ligament has been documented.67 Loss of periodontal ligament proprioception that occurs when the natural teeth are lost has been described as an important consideration in the replacement of natural teeth with dental implants. Studies that have examined tactile sensibility have demonstrated extreme differences between natural teeth and implants (average 3.8-g pressure for natural teeth tested horizontally vs. 580-g horizontal force for implants in the anterior mandible).68-70 In spite of these findings, patients with extensive implantsupported restorations seem, clinically, to function well without the benefit of periodontal proprioceptive nerve endings. The presence of proprioceptive nerve endings in periosteum, muscles of mastication, oral mucosa, and the temporomandibular joints may somewhat compensate for those lost from the missing periodontal ligament. There is, in fact, extensive discussion on the topic of ‘‘osseoperception’’ in the literature,71-74 including a textbook on the subject.75

SUMMARY Little scientific evidence supports a direct cause-effect relationship between occlusal factors and deleterious biological outcomes for osseointegrated implants. To the contrary, the limited evidence available at this time supports the position that there is no direct cause-effect relationship between occlusion and disease processes. Evidence supporting specific occlusal theories for removable prostheses is primarily based on expert opinion and in vitro studies. Evidence supporting specific occlusal theories for implant-supported prostheses is based on expert opinion, in vitro studies, and animal studies. REFERENCES 1. Sadowsky SJ. The role of complete denture principles in implant prosthodontics. J Calif Dent Assoc 2003;31:905-9. 2. Mann AW, Pankey LD. Oral rehabilitation–Part I. Use of the P-M instrument in the treatment planning and in restoring the lower posterior teeth. J Prosthet Dent 1960;10:135-50. 3. Glossary of prosthodontic terms. 8th ed. J Prosthet Dent 2005;94:17. 4. Kurth LE. Balanced occlusion. J Prosthet Dent 1954;4:150-67. 5. Hanau RL. Articulation defined, analyzed, and formulated. J Am Dent Assoc 1926;13:1694-709. 6. Sheppard IM, Rakoff S, Sheppard SM. Bolus placement during mastication. J Prosthet Dent 1968;20:506-10. 7. Brewer AA, Hudson DC. Application of miniaturized electronic devices to the study of tooth contact in complete dentures: a progress report. J Prosthet Dent 1961;27:62-72.

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8. Boucher CO. Jaw relations and occlusion in complete dentures. Introduction to the symposium. J Prosthet Dent 1955;5:299-300. 9. Payne SH. Selective occlusion. J Prosthet Dent 1955;5:301-4. 10. Pleasure MA. Occlusion of cuspless teeth for balance and comfort. J Prosthet Dent 1955;5:305-12. 11. Porter CG. The cuspless centralized occlusal pattern. J Prosthet Dent 1955;5:313-8. 12. Shanahan TEJ. Physiologic jaw relations and occlusion of complete dentures. J Prosthet Dent 1955;5:319-24. 13. Trapozzano VR. Occlusal records. J Prosthet Dent 1955;5:325-32. 14. Lang BR, Kelsey CC, editors. International prosthodontic workshop on complete denture occlusion. Ann Arbor: University of Michigan School of Dentistry; 1973. p. 1-338. 15. Kapur KK. Occlusal patterns and tooth arrangements. In: Lang BR, Kelsey CC, editors. International prosthodontic workshop on complete denture occlusion. Ann Arbor: University of Michigan School of Dentistry; 1973. p. 145-72. 16. Bascom PW. Masticatory efficiency of complete dentures. J Prosthet Dent 1962;12:453-9. 17. Sauser CW, Yurkstas AA. The effect of various geometric occlusal patterns on chewing efficiency. J Prosthet Dent 1957;7:634-45. 18. Trapozzano VR, Lazzari JB. An experimental study of the testing of occlusal patterns on the same denture bases. J Prosthet Dent 1952;2:440-57. 19. Trapozzano VR. Testing of occlusal patterns on the same denture base. J Prosthet Dent 1959;9:53-69. 20. Trapozzano VR. Tests of balanced and nonbalanced occlusions. J Prosthet Dent 1960;10:476-87. 21. Yurkstas AA, Manly RS. Value of different test foods in estimating masticatory ability. J Appl Physiol 1950;3:45-53. 22. Yurkstas AA. The influence of geometric occlusal carvings on the masticatory effectiveness of complete dentures. J Prosthet Dent 1963;13:452-61. 23. Manly RS, Vinton P. A survey of the chewing ability of denture wearers. J Dent Res 1951;30:314-21. 24. Kapur KK, Soman S. Masticatory performance and efficiency in denture wearers. 1964. J Prosthet Dent 2004;92:107-11. 25. Kapur KK, Soman S. The effect of denture factors on masticatory performance. 3. The location of the food platforms. J Prosthet Dent 1965;15:451-63. 26. Kapur KK, Soman S. The effect of denture factors on masticatory performance. IV. Influence of occlusal patterns. J Prosthet Dent 1965;15:662-70. 27. Kapur KK, Soman S, Shapiro S. The effect of denture factors on masticatory performance. V. Food platform area and metal inserts. J Prosthet Dent 1965;15:857-66. 28. Kydd WL. The Comminuting efficiency of varied occlusal tooth form and the associated deformation of the complete denture base. J Am Dent Assoc 1960;61:465-71. 29. Swoope CC, Kydd WL. The effect of cusp form and occlusal surface area on denture base deformation. J Prosthet Dent 1966;16:34-43. 30. Woelfel JB, Hickey JC, Allison ML. Effect of posterior tooth form on jaw and denture movement. J Prosthet Dent 1962;12:922-39. 31. Smith DE, Kydd WL, Wykhius WA, Phillips LA. The mobility of artificial dentures during comminution. J Prosthet Dent 1963;13:839-56. 32. Brewer AA, Reibel PR, Nassif NJ. Comparisons of zero degree and anatomic teeth on complete dentures. J Prosthet Dent 1967;17:28-35. 33. Thompson MJ. Masticatory efficiency as related to cusp form in denture prosthesis. Dent Cosmos 1937;24:207-19. 34. Carlsson GE. Masticatory efficiency: the effect of age, the loss of teeth and prosthetic rehabilitation. Int Dent J 1984;34:93-7. 35. Slagter AP, Olthoff LW, Steen WH, Bosman F. Comminution of food by complete-denture wearers. J Dent Res 1992;71:380-5. 36. Gunne HS, Bergman B, Enbom L, Hogstrom J. Masticatory efficiency of complete denture patients. A clinical examination of potential changes at the transition from old to new denture. Acta Odontol Scand 1982;40: 289-97. 37. Lundquist LW, Carlsson GE, Hedegard B. Changes in bite force and chewing efficiency after denture treatment in edentulous patients with denture adaptation difficulties. J Oral Rehabil 1986;13:21-9. 38. Peroz I, Leuenberg A, Haustein I, Lange KP. Comparison between balanced occlusion and canine guidance in complete denture wearersâ&#x20AC;&#x201D;a clinical, randomized trial. Quintessence Int 2003;34:607-12. 39. Jacob RF. The traditional therapeutic paradigm: complete denture therapy. J Prosthet Dent 1998;79:6-13. 40. Guerra L, Finger I. Principles of implant prosthodontics. In: Block MS, Kent JN, Guerra LR, editors. Implants in dentistry. Philadelphia: WB Saunders; 1997. p. 81.

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41. Jimenez-Lopez V, Keogh TP. Oral rehabilitation with implant-supported prostheses. Chicago: Quintessence; 1999. p. 78. 42. Rangert B, Jemt T, Jorneus L. Forces and moments on Branemark implants. Int J Oral Maxillofac Implants 1989;4:241-7. 43. Burke T, Schnader Y. Occlusal considerations to prevent prosthesis and component complications. In: Zinner IO, editor. Implant dentistry: from failure to success. Chicago: Quintessence; 2004. p. 96. 44. Hobo S, Ichida E, Garcia L. Osseointegration and occlusal rehabilitation. Chicago: Quintessence; 1989. p. 260. 45. Rosenstiel SF, Land MF, Fujimoto J. Contemporary fixed prosthodontics. 3rd ed. St. Louis: Mosby; 2001. p. 347. 46. Celletti R, Pameijer CH, Bracchetti G, Donath K, Persichetti G, Visani I. Histologic evaluation of osseointegrated implants restored in nonaxial functional occlusion with preangled abutments. Int J Periodont Restorative Dent 1995;15:563-73. 47. Brunski J. Biomechanics of dental implants. In: Block M, Kent J, editors. Endosseous implants for maxillofacial reconstruction. Philadelphia: WB Saunders; 1995. p. 63-73. 48. Jemt T, Lekholm U, Johansson C. Bone response to implant-supported frameworks with differing degrees of misfit preload: in vivo study in rabbits. Clin Implant Dent Relat Research 2000;2:129-37. 49. Jemt T, Lundquist S, Hedegard B. Group function or canine protection. J Prosthet Dent 1982;48:719-24. 50. Asikainen P, Klemetti E, Vuillemin T, Sutter F, Rainio V, Kotilainen R. Titanium implants and lateral forces. An experimental study with sheep. Clin Oral Implants Res 1997;8:465-8. 51. Misch CE. Dental implant prosthetics. St. Louis: Mosby; 2004. p. 511-30. 52. Binon P, Sullivan DY. Provisional fixed restorations technique for osseointegrated implants. J Calif Dent Assoc 1990;18:28-30. 53. Finger I, Guerra L. Implants in dentistry. In: Block M, Kent J, Guerra L, editors. Philadelphia: WB Saunders; 1997. p. 143. 54. Roberts WE, Turley P, Brezniak N, Fielder P. Implants: bone physiology and metabolism. CDA J 1987;15:54-61. 55. Ogiso M, Tabata T, Kuo P, Borgese D. A histologic comparison of the functional loading capacity of an occluded dense apatite implant and the natural dentition. J Prosthet Dent 1994;71:581-8. 56. Miyata T, Kobayashi Y, Araki H, Motomura Y, Shin K. The influence of controlled occlusal overload on peri-implant tissue: a histologic study in monkeys. Int J Oral Maxillofac Implants 1998;13:677-83. 57. Hurzeler MB, Quinones CR, Kohal RJ, Rohde M, Strub JR, Teuscher U, et al. Changes in peri-implant tissues subjected to orthodontic forces and ligature breakdown in monkeys. J Periodontol 1998;69:396-404. 58. Isidor F. Loss of osseointegration caused by occlusal load of oral implants. A clinical and radiographic study in monkeys. Clin Oral Implants Res 1996;7:143-52. 59. Heitz-Mayfield LJ, Schmid B, Weigel C, Gerber S, Bosshardt DD, Jonsson J, et al. Does excessive occlusal load affect osseointegration? An experimental study in the dog. Clin Oral Implants Res 2004;15:259-68. 60. Berglundh T, Abrahamsson I, Lindhe J. Bone reactions to longstanding functional load at implants: an experimental study in dogs. J Clin Periodontol 2005;32:925-32. 61. Skalak R. Aspects of biomechanical considerations. In: Branemark PI, Zarb G, Albrektsson T, editors. Tissue integrated prostheses: osseointegration in clinical dentistry. Chicago: Quintessence; 1985. p. 117-28. 62. Bassit R, Lindstrom H, Rangert B. In vivo registration of force development with ceramic and acrylic resin occlusal materials on implant-supported prostheses. Int J Oral Maxillofac Implants 2002;17:17-23. 63. Hurzeler M, Quinones C, Schupbach P, Vlassis J, Strub J, Caffesse R. Influence of the suprastructure on the peri-implant tissues in beagle dogs. Clin Oral Implants Res 1995;6:139-48. 64. Stegaroiu R, Khraisat A, Nomura S, Miyakawa O. Influence of superstructure materials on strain around an implant under 2 loading conditions: a technical investigation. Int J Oral Maxillofac Implants 2004;19: 735-42. 65. Richter E. In vivo vertical forces on implants. Int J Oral Maxillofac Implants 1995;10:99-108. 66. Richter E. In vivo horizontal bending moments on implants. Int J Oral Maxillofac Implants 1998;13:232-44. 67. Jacobs R, van Steenberghe D. Role of periodontal ligament receptors in the tactile function of teeth: a review. J Periodontal Res 1994;29:153-67. 68. Mericske-Stern R, Hofmann J, Wedig A, Geering A. In vivo measurements of maximal occlusal force and minimal pressure threshold on overdentures supported by implants or natural roots: a comparative study, Part 1. Int J Oral Maxillofac Implants 1993;8:641-9.

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69. Mericske-Stern R, Assal P, Mericske E, Burgin W. Occlusal force and oral tactile sensibility measured in partially edentulous patients with ITI implants. Int J Oral Maxillofac Implants 1995;10:345-53. 70. Hammerle CH, Wagner D, Bragger U, Lussi A, Karayiannis A, Joss A, et al. Threshold of tactile sensitivity perceived with dental endosseous implants and natural teeth. Clin Oral Implants Res 1995;6:83-90. 71. El-Sheikh A, Hobkirk JA, Howell PG, Gilthorpe MS. Passive sensibility in edentulous subjects treated with dental implants: a pilot study. J Prosthet Dent 2004;91:26-32. 72. Jacobs R, Branemark R, Olmarker K, Rydevik B, van Steenberghe D, Branemark PI. Evaluation of the psychophysical detection threshold level for vibrotactile and pressure stimulation of prosthetic limbs using bone anchorage or soft tissue support. Prosthet Orthot Int 2000;24:133-42. 73. Van Loven K, Jacobs R, Swinnen A, Van Huffel S, Van Hees J, van Steenberghe D. Perception through oral osseointegrated implants demonstrated by somatosensory-evoked potentials. Arch Oral Biol 2000;45:1083-90. 74. Jacobs R, Wu C-H, Goossens K, Van Loven K, van Steenberghe D. Perceptual changes in the anterior maxilla after placement of endosseous implants. Clin Implant Dent Relat Res 2001;3:148-55.

Noteworthy Abstracts of the Current Literature

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75. Jacobs R. Osseoperception. Department of Periodontology. Leuven: KU Leuven; 1998. Reprint requests to: DR THOMAS D. TAYLOR DEPARTMENT OF ORAL REHABILITATION BIOMATERIALS AND SKELETAL DEVELOPMENT UNIVERSITY OF CONNECTICUT SCHOOL OF DENTAL MEDICINE 263 FARMINGTON AVE FARMINGTON, CT 06030-1615 FAX: 860-679-1370 E-MAIL: ttaylor@nso.uchc.edu 0022-3913/$30.00 Copyright Ă&#x201C; 2005 by The Editorial Council of The Journal of Prosthetic Dentistry.

doi:10.1016/j.prosdent.2005.10.012

Clinical case reports of injectable tissue-engineered bone for alveolar augmentation with simultaneous implant placement Ueda M, Yamada Y, Ozawa R, Okazaki Y. Int J Periodontics Restorative Dent 2005;25:129-37.

This clinical study was undertaken to evaluate the use of tissue-engineered bone, mesenchymal stem cells, platelet-rich plasma, and beta-tricalcium phosphate as grafting materials for maxillary sinus floor augmentation or onlay plasty with simultaneous implant placement in six patients with 3- to 5-mm alveolar crestal bone height. All 20 implants were clinically stable at second-stage surgery and 12 months postloading. A mean increase in mineralized tissue height of 7.3 6 4.6 mm was evident when comparing the pre- and postsurgical radiographs. Injectable tissue-engineered bone provided stable and predictable results in terms of implant success.â&#x20AC;&#x201D;Reprinted with permission of Quintessence Publishing.

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chapter 10

Evidence-Based Medicine Applied to Fixed Prosthodontics Asbjørn Jokstad

People who seek help from professionals have a right to expect that formal measures have been taken to assess the relative merits of the various forms of health care on offer, be these, for example, radical surgery or fixed prosthodontics.1 There is increasingly wide support for the principle of reliable assessment of the effects of health and social interventions on outcomes that matter to the people to whom they are offered. Debate continues, however, about the methods of assessment that should be used in implementing this principle in practice. Different strategies for improving treatment effectiveness and quality have been proposed under different names. “Outcome research”, “technology assessment methodology”, “quality management and assurance”, “clinical guidelines”, “parameters of care”, “health economy analyses”, etc. are familiar terms. Which strategy is selected and, perhaps more important, funded, is influenced by current beliefs and priorities in society. However, a common denominator of the different strategies is the concern about the appropriateness of care, whether on an individual or on a population level. It is in this context that a new strategy for teaching the practice of medicine, named evidence-based medicine (EBM), was introduced in 1991 at the McMaster University in Canada.2 The rationale for changing the teaching strategy was the assumption that although traditional medical training resulted in a more-or-less thorough understanding of basic mechanisms of disease and pathophysiological principles, this combined with common sense and unsystematic observations from one’s own clinical experience did not prepare the physician for assessing and evaluating the new diagnostic tests, treat337

ments and guidelines for clinical practice continuously presented in the scientific literature. Thus, it was assumed that teaching the medical students instead how to critically appraise medical information for its validity and usefulness and incorporate this evidence into oneâ&#x20AC;&#x2122;s clinical practice would produce physicians capable of life-long self-directed learning resulting in superior patient care.5 Since its introduction, the principles of EBM have been applied in other biomedical areas, and named thereafter. We have journals named evidence-based nursing and evidence-based mental health, textbooks entitled evidence-based health care and evidence-based health promotion, and disciplines termed evidence-based physiotherapy and evidence-based dentistry, etc. Although the proliferation of different terms can be questioned, the main aims remain the same, to identify and apply the current best evidence in making decisions about the care of our patients. This should also be applied to fixed prosthodontics.

Characteristics of Fixed Prosthodontics Prosthodontics can be defined as: â&#x20AC;&#x153;The discipline of dentistry concerned with the consequences of congenital absence or acquired loss of oral tissues for appearance, stomatognathic function, comfort, and local and general health of the patient, and with the assessment of whether more good than harm is done by inserting artificial devices made from alloplastic materials to change these conditionsâ&#x20AC;?.3 In fixed prosthodontics, precise and clinically accurate operative techniques based on sound biological and mechanical principles are used to achieve this goal with fixed artificial devices. Advances in the discipline rely on research in multiple technical sciences such as chemistry, physics, biomaterial research etc, since critical decisions made to achieve aesthetic and functional goals must be within the limitations of available restorative materials. The practice of fixed prosthodontics, however, lies in the borderline zone between health, illness and disease, and therefore needs to draw on theories not only from biomedical research, but also from the humanities (psychology, philosophy and ethics), the social sciences (sociology, anthropology) and the organisational sciences. Knowledge is needed about help-seeking behaviour, doctor-patient interaction and clinical decision-making, and the process of quality development, implementation of new skills and technology, cost effective audit and continuing education. Dentists engaged in prosthodontics benefit from training in key theoretical and practical concepts, e.g. communication theories, health beliefs, coping, stress, somatisation, empowerment, health technology assessment, quality development, health economy and prioritysetting. 338

The dentist relies more or less consciously on the knowledge from these disciplines and key concepts when faced with daily obligations to: 1. identify the individual patient’s problems, needs and preferences, 2. make a thorough examination and correct diagnosis and advocate an optimal therapy based on the treatment outcome and prognosis of the different possibilities, and 3. discuss the treatment options, of which fixed prosthodontics may be one of several, with the patient, keeping the focus on patient-relevant factors. We would probably all agree that, if placing ourselves in the patient’s place, we whould like to be treated according to the best available scientific evidence on the accuracy and precision of diagnostic tests, the power of prognostic markers and the efficacy and safety of therapeutic, rehabilitative and preventive measures. In addition, we would prefer a clinician who integrates this with thoughtful identification and compassionate consideration of our predicament, rights and preferences in making clinical decisions about our care.4 Although this has always been the aim of conscientious clinicians, practice according to these principles is hampered by several difficulties. The most fundamental problem is perhaps the lack of training in critical appraisal of new, primarily scientific information among the front-line (bio)medical professions. However, more disturbing is the lack of sound scientific evidence relevant to diagnosis, prognosis and treatment of patients in all areas of medicine5, including the multidimensional perspectives relevant to fixed prosthodontics .

What is the Basis of Our Knowledge of Fixed Prosthodontics ? Dental School Training The production of new medical information has never before been as high, and there is no reason to suppose that it will diminish. An anecdote refers to the dean of a medical school who proclaimed to the new students that 50 per cent of everything they would learn in the next few years would be outdated and wrong by the time they started practising – unfortunately nobody knew which 50 per cent. In spite of this, most dentists have their greatest theoretical knowledge at the time of graduation. From then on, time to acquire more theoretical knowledge becomes scarce. During dental school training the teaching is focussed on how to execute basic, “safe” clinical procedures, which are not necessarily the most modern ones. Students learn to place conventional dental materials in a variety of situations instead of more lengthy and technique-sensitive procedures for ceramic restorations.6 Furthermore, many treatment procedures carried out in general practice have not been given 339

any room in the tightly packed curricula in many dental schools, for various reasons. Examples are membrane augmentation and implant-supported partial dentures. Thus, right from their graduation day, dentists need to improve their technical and theoretical clinical skills. The problem is where to go and how to proceed to obtain the necessary knowledge, and how to allocate limited and precious time to do it.

The Scientific Literature The scientific literature comprises 20 000 biomedical journals with 2 million papers per year, including 500 dental journals with 50 000 articles per year. Since it is obviously impossible to read, or even scan the abstract of, 140 papers every day, we need to focus on the quality of the information we receive rather than the quantity. Another strategy is to focus on reading the journals that include secondary papers, e.g. Evidence-Based Dentistry, which limits its contents to studies in oral medicine satisfying generally accepted criteria for good scientific quality. Review papers are by many regarded as helpful guides for their own practice. However, many review papers are heavily author-biased. A review paper must satisfy two basic requirements: the clinical topic being reviewed must be clearly stated and there must be a description of how the evidence on this topic was obtained, from what sources and with which inclusion and exclusion criteria. A check-list for critically assessing a review paper is presented in Table 1. Systematic reviews are reviews carried out and presented according to specific criteria, e.g. described by the international Cochrane Collaboration (http://www.cochrane.dk). At present, very few systematic reviews have been carried out in oral medicine, but this will change in the near future. Some reviews include data accumulated data from individual studies, which is termed carrying out a meta-analysis. Meta-analyses can be helpful when properly made, but are worthless if inappropriately applied. Clinical Experience The fallacy of using an approach to treat patients based on previous clinical experience is summed up by Charles S Greene: “The expression “it works in my hands” seems to serve as a standard of validity for some people, despite the fact that a positive clinical response may be obtained either because of, in spite of, or irrespective of the treatment rendered”.7 Apparent success must be evaluated relative to factors such as spontaneous remission, placebo response and multiple variables of treatment: radical versus conservative treatment, over-treatment, long-term failure and side effects and sequelae of treatment. On the other hand, failure can be related to incorrect diagnosis, incorrect cause-effect correlation, multifactorial problems, lack of co-operation, improper 340

Table 1. Checklist for critical appraisal of review articles (adapted from Sackett et al.4) Are the results of the review valid? 1. Did the review address a clearly focussed issue?

Yes

Can’t tell

Yes

Can’t tell

Yes

Can’t tell

4. Did the review’s authors do enough to assess the quality of the studies included?

Yes

Can’t tell

5. Were the results similar from study to study?

Yes

Can’t tell

Yes

Can’t tell

Yes

Can’t tell,

Yes

Can’t tell

An issue can be focussed in terms of - the population studied - the intervention given - the outcomes considered

2. Did the authors select the right sort of studies for review? The right sort of studies would - address the review’s question - have an adequate study design

3. Do you think the important, relevant studies were included? look for - which bibliographic databases were used - check from reference lists - personal contact with experts - search for unpublished as well as published studies - search for non-English language studies

Consider whether - the results of all the studies included are clearly displayed - the results of the different studies are similar - the reasons for any variations in results are discussed

What are the results? 6. What is the overall result of the review? Consider - if you are clear about the review’s bottom line results what these are (numerically if appropriate) what units these results are expressed in

7. How precise are the results ? Are there confidence limits? What are they?

Will the results help my patients? 8. Can the results be applied to my patients? Do you think that the patients covered by the trial are similar enough to your population?

9. Were all clinically important outcomes considered? If not, does this affect the decision?

10. Are the benefits worth the harms and costs? This is unlikely to be addressed by the trial. But what do you think?

341

execution of treatment, premature evaluation of treatment, limited success of treatment and psychological barriers to success. Unsystematic observations from clinical experience are not a valid way of building and maintaining one’s knowledge about patient prognosis, the value of diagnostic tests, and the efficacy of treatment.5

Clinical Guidelines, Standard Operating Procedures, Parameters of Care, etc. Although the development and use of practice-related guidelines as educational aids have a long history in the health professions, scientific assessments indicate that they have limited success in changing daily practice. A major reason is the lack of knowledge needed to develop guidelines that have to be accepted by the profession.8 A check-list for critically assessing guidelines is presented in Table 2. Guidelines developed by professional dental organisations specific to oral health are rare, and almost non-existent in the field of prosthodontics. The few existing guidelines have mostly been developed using a consensus approach. A problem when using a consensus approach is that it does not guarantee clinical applicability, reliability and validity. The Canadian Dental Association’s Ad Hoc Committee on Clinical Practice Guidelines is currently developing guidelines in dentistry, but has encountered many setbacks during the work. The British Society for Restorative Dentistry has developed “Guidelines for Crowns and Bridgework” and “A Strategy For Planning Restorative Dental Care” (http://www.derweb.ac.uk/bsrd/index.html). In the USA, the American College of Prosthodontics has formulated the “principles, concepts and practices in prosthodontics”, but the speciality does not formally recognise these as guidelines.

Appraisal of the Scientific Basis for Decision-Making in Fixed Prosthodontics The following elements are involved in the treatment of patients with fixed prosthodontics (Table 3) and can serve as a framework for a critical appraisal of the scientific foundation of the treatment: I. The patient’s problem versus identification of need • Patient differences and reasons for variations in perceived problems caused by missing oral tissue The everyday-working situation of the dentist is complex, especially when treating patients seeking professional help due to the physical, psychological or social manifes342

tations of missing hard and soft oral tissues. Missing oral tissue per se is not, and seldom leads to, a pathophysiological process. As a consequence, prosthodontics should be regarded as elective and the patient’s values and preferences must influence all treatment decisions. Also, because prosthodontics is associated with high costs, economic constraints often influence the treatment decisions. Different aims and study designs can be used to clarify these questions. The preferred study design is cross-sectional survey or cohort studies. The perceived need for treatment varies among both patients and dentists. Some interesting high-quality studies from Sweden have focussed on the marked variation among

Table 2. Checklist for critical appraisal of clinical practice guidelines (adapted from Sackett et al.4). Are the clinical practice guidelines valid? 1. Were all important options and issues clearly specified?

Yes

Can’t tell

2. Was an explicit and sensible process used to identify, select and combine evidence?

Yes

Can’t tell

3. Was an explicit and sensible process used to consider the relative value of different outcomes?

Yes

Can’t tell

4. Is the guideline likely to account for important recent developments?

Yes

Can’t tell

5. Has the guideline been subject to peer review and testing?

Yes

Can’t tell

Yes

Can’t tell

Yes

Can’t tell

Yes

Can’t tell

What are the recommendations? 6. Are practical, clinically important recommendations made? 7. How strong are the recommendations ? 8. What is the impact of uncertainty associated with the evidence and values used in the guidelines? Will the recommendations help my patients? 9. Is the primary objective of the guideline consistent with your objective? 10. Can the recommendations be applied to my patients?

343

patients’9, as well as dentists’10 expectations, values and priorities that definitely influence treatment decisions, therapy, patient compliance, costs, the risk of malpractice suits, etc. • Patient education The effectiveness of various methods of motivating and educating patients should be addressed, using appropriate study designs. The preferred study design is randomised controlled trials. A disturbing conclusion reported recently is that many strategies for prophylactic activity may perhaps be of limited value for motivating patients to adopt and maintain good oral health.11

Table 3. Elements involved in fixed prosthodontics I. The patient’s problem versus identification of need • Patient differences and reasons for variations in perceived problems caused by missing oral tissue • Patient education II. Therapeutic aims • Criteria used to define need vs. outcome Morphological, functional, esthetic, psychometric, subjective How valid and reproducible are these criteria? Who should define “minimum satisfactorily” outcome criteria? • Cost-efficiency and -utility versus other treatment alternatives III. Procedures for producing fixed prostheses • Diagnostics of the occlusion and quality of abutment teeth • Technical procedures, and risk for technical and biological complications The clinic The laboratory 1. choice of preprosthetic endodontics 2. choice of posts and cores 3. choice of biomaterials 4. adequate tooth preparation (technique) 5. choice of impression (material/technique) 6. choice of die material 7. choice of investment 8. choice of casting 9. choice of interim solution 10. choice of cementation (material/technique) 11. choice of adequate maintenance IV. Identification of outcome • To what extent are treatment aims reached • Adverse reactions, longevity and risk for technical and biological complications 344

II. Therapeutic aims • Criteria used to define need vs. outcome The key determinants of need for, as well as assessment of the outcomes of, fixed prosthodontics reflect both patients’ – and dentists’ concerns: 1. Physiological impact: Satisfactory and comfortable mastication, i.e. efficiency, bite force, maintenance of remaining tissues, effect on diet, etc. 2. Psychological impact: orofacial body image, perceived quality of life, perceived satisfaction with prostheses, self-esteem and interpersonal relations, etc. 3. Longevity/survival: minimal risk of morbidity, provisions for easy and routine patient and dentist maintenance, provisions for planned and unplanned design modifications, time-dependent wear-and-tear concerns in varying and variable intraoral environments that may become increasingly unpredictable in the context of an individual patient’s biological and chronological aging, etc. 4. Economic impact: Direct cost of treatment, maintenance costs, indirect costs. Several questions can be raised, and best answered using cross-sectional surveys. The literature describes criteria for evaluating both need for treatment and treatment outcome that can be categorised as morphological, functional, aesthetic, psychometric or patient-subjective criteria. Major questions in this context are how valid and reproducible these criteria are and who should define the “minimum satisfactory” outcome criteria of fixed prosthodontics? Is it the patient, the clinician, society or the insurance companies? As in other areas of medicine, much attention is addressed to patient-selected criteria for treatment success as an adjunct to, or even in contrast to, the professionals’ criteria. However, many problems arise because of the previously identified variations in patients’ values and priorities. Also, patient satisfaction is the result of many other factors besides the actual care that is given12, which confounds the interpretation of patient-selected criteria for treatment success. This is partly the reason why there are many objections to the increased emphasis on so-called quality-of-life analyses in medicine and to a limited extent in dentistry.13 • Cost-efficiency and utility versus other health care alternatives The preferred study design is randomised controlled trials. Some studies have compared the prognoses of conventional versus other variants of fixed partial dentures, for example, resin-bonded14 or implant-supported.15 Problems with such comparisons are differences in study design, the selection of patients and the criteria of treatment success and outcome. On top of this, differences in patients’ values and prefer-

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Table 4. Specific criteria needed to be completed for studies to be considered as good evidence. 1. Clinical findings 2. Diagnostic tests 3. Differential diagnosis

• clearly identified comparison groups, at least one of which is free from the target disorder or derangement; either an objective diagnostic standard (e.g. machine-produced laboratory result) or a contemporary clinical diagnostic standard with demonstrably reproducible criteria for any objectively interpreted component (e.g. report of better-than-chance agreement among interpreters); • interpretation of the test without knowledge of the diagnostic standard result; • interpretation of the diagnostic standard without knowledge of the test result; • an analysis consistent with the study design; • for pre-test probabilities, also a consecutive series or random sample of patients from a clearly defined setting.

4. Etiology

• clearly identified comparison group for those at risk for, or having, the outcome of interest (whether from randomised, quasirandomised or non-randomised); • controlled trials; cohort-analytic studies with case-by-case matching or statistical adjustment to create comparable groups; or casecontrol studies; • masking of observers of outcomes to exposures (this criterion is assumed to be met if the outcome is objective [e.g. all-cause mortality or an objective test]); • observers of exposures masked to outcomes for case-control studies and subjects masked to exposure for all other study designs; • interpretation of the diagnostic standard without knowledge of the test result; • an analysis consistent with the study design.

5. Therapy 7. Prevention 8. Education

• random allocation of the participants to the different interventions; • outcome measures of known or probable clinical importance for at least 80 per cent of participants who entered the investigation; • an analysis consistent with the study design.

6. Prognosis

• an inception cohort of persons, all initially free of the outcome of interest; • follow-up of at least 80 per cent of patients until the occurrence of either a major study endpoint or the end of the study; • an analysis consistent with the study design.

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ences confound such analyses, since they will indirectly influence both the choice of treatment and the patient’s satisfaction with the treatment.16 III. Procedures for producing fixed partial dentures • Diagnosis of the occlusion and quality of abutment teeth The preferred study design is a cross-sectional study where potential new concepts and procedures for diagnosis must be validated as described in Table 4. • Technical procedures, and the risk of technical and biological complications during the treatment process The preferred study design is randomised-controlled trials. During the last 15 years numerous new concepts using different dental materials and and/or procedures have been developed and disappeared. It is remarkable that, except for a few products, scientific grounds for advocating these concepts are lacking. Some thirty alternatives to conventional metal-ceramic crowns have been described but very few are supported by sound clinical data. Similar tables can be made for impression materials and procedures, bite registration techniques, gingival retraction management, cements and cementation methods, interim materials, etc., with even fewer references to sound clinical studies. Other reports that embrace other disciplines of dentistry show that even though traditional solutions often work better, many dentists still prefer to use modern and unproven solutions for their patients, e.g. a post and core.17 The reason for this situation remains uncertain but many have speculated that the lack of training in critical appraisal of information in the dental school curriculum may explain the phenomenon. IV. Judging the outcome • To what extent are treatment objectives achieved? The determinants of success of fixed prosthodontic treatment are identical to the determinants of treatment needs, including the validity, reliability and relevance to the patient, the clinician and society. Again, the patient’s values and preferences are of prime importance when addressing these issues.18 The preferred study design is randomised controlled trials or longitudinal cohort studies, but some problems may also best be elucidated using cross-sectional data. Several meta-analyses show marked variations of prognosis due to differences in patients, materials and operators for conventional tooth-supported fixed partial dentures19,20, veneers21 and implant-toothbased FPDs or implant-based single crowns.22

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â&#x20AC;˘ Adverse reactions, longevity and risk of technical and biological complications The preferred study design is randomised controlled trials or longitudinal cohort studies, but hypotheses can also be developed from data recorded in cohort and caseseries and case-controlled studies.

EBM Applied to Fixed Prosthodontics Application of EBM to fixed prosthodontics is done by conscientiously asking oneself the following questions in actual clinical situations when a need for information arises before making a clinical decision:2 1. How can I convert information needs into answerable questions? 2. How can I track down, with maximum efficiency, the best evidence with which to answer them (whether from the clinical examination, the diagnostic results, the published literature, or other sources)? 3. How can I critically appraise the evidence for its validity (closeness to the truth) and usefulness (clinical applicability)? 4. How can I apply the results of this appraisal in this particular clinical situation? Integration of these questions with the individual elements that form treatment decisions for individual patients is one way of describing the practice of EBM (Fig. 1). It is apparent that EBM is not a type of cookbook medicine, but rather a strategy for integrating the best available external evidence from systematic research with individual clinical expertise. EBM is a strategy for coping with new information; it is not about knowing all the answers. Thus, it is not so much about what you have read in the past, but about how you go about identifying and meeting your ongoing learning needs and applying your new knowledge appropriately and consistently in new clinical situations. Consider the following patient situation: Eva Karlsson is a 45-year-old woman who has had all her amalgam restorations removed and replaced these with non-metal materials. She now wants a fixed partial denture to close a space and would like your opinion on the benefits and disadvantages of choosing a non-metal appliance (which she intuitively would prefer, but knows nothing about).

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Situation: question of intervention

6. What is the quality? How up to date?

Abilities: Diagnostic Communicative Empathy Observational

â&#x20AC;&#x153;Knowledgeâ&#x20AC;? Need for information questions

1. How to construct answerable questions?

What has been published?

2. Where and how to track down the information needed?

What is the clinical validity?

3. How to do a critical appraisal?

What is the clinical applicability?

4. How to apply the results of the appraisal to your patient?

Clinical experience, time, selfconfidence, persuasivness, etc.

Decision: alternative interventions

Patient values, preferences, priorities, economy, etc.

Fig 1. The elements of EBM applied to the daily work situation as clinicians.

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1. Posing answerable questions Well-formulated clinical questions should be directly relevant to the problem at hand and phrased to facilitate searching the literature for a precise answer. To achieve these aims, the questions must be focused and well articulated and cover the following issues: 1.The patient or problem being addressed: How would I describe a group of patients similar to mine? 2.The intervention or exposure being considered: Which main intervention, prognostic factor or exposure am I considering? 3.Comparison of the intervention or exposure with alternatives, when relevant: What is the main alternative to compare with the intervention? 4. The clinical outcome: What can I hope to accomplish, measure, improve or affect? Applying these questions to our example needs perhaps some clarification from the patient regarding her values and priorities – does she emphasise concern about, for example, the aesthetics, prognosis or potential adverse effects of metal-ceramic fixed dentures? Let us assume that the primary concern for this particular patient is the longevity. Thus, our clinical questions could be formulated as follows: In adult patients, what is the longevity of full-ceramic fixed partial dentures compared to metal-ceramic appliances? Two further questions can be posed, which will apply directly to the type of research being most relevant: what type of clinical problem am I faced with and what would be the best study design in order to obtain the information needed (Table 4)? Since this is a question of the outcome of a therapy, the best evidence for effectiveness is observations made in randomised controlled trials. 2. Tracking down evidence Advances in computer technology have improved the possibility of effectively tracking down the evidence from the rapidly growing body of medical information. Due to ease of access, Internet has become the highway to information abou just about anything, including oral health. Internet search robots, e.g. Altavista, Excite, Infoseek, Lycos, Medcrawler, Netscape, Snap, etc., facilitate the search and can produce large numbers of references. Unfortunately, it takes time and energy to sort out important information, time which most people don’t have. Another strategy is therefore to link up to medical search engines or large dental sites, which presumably have such information sorted out by the use of different “quality criteria”. The greatest value of using the Internet is the possibility to gain direct access to 350

large encyclopaedias and databases of scientific literature, material properties, toxicology etc. Perhaps the most important information can be located in Medline; the bibliographic database administrated by the US National Library of Medicine, NLM. (http://www.nlm.nih.gov/databases/freemedl.html). Use of the Medline is free, and can easily be done without much prior experience by using the two searching softwares offered by NLM, Pubmed and Internet Grateful Med. Our search in the Medline database resulted in finding 5865 papers focussed on fixed partial dentures and 7778 on ceramics. Combining these two search terms and limiting the search to randomised controlled trials reduced the number of papers to 3, of which only one was relevant for us. By also including controlled trials, the number of studies increased to 12. In addition, a search for potentially interesting reviews on the topic resulted in 17 papers. In this particular search, the software Ovid was used (http:// gateway.ovid.com). However, about identical numbers would be located if Pubmed or Internet Grateful Med had been used. 3. Critical appraisal of information Most dentists are aware that progress is based upon scientific research. Even “instants of perception” must be backed up by tedious research in order to persuade colleagues, third party payers and patients of hypothetical relationships. There are no laws against constructing hypotheses, even when unscientifically founded, which signifies that a hypothesis is worth just as much as the relevance and validity of the science upon which it is based. The difficult part is to validate a hypothesis, which in modern medicine is preferably done by carrying out research using accepted scientific standards. Unless these standards are adhered to, studies may mislead instead of elucidating improved health care.23 Research studies focused on fixed prosthodontics can be categorised as laboratory (or in-vitro) studies or as clinical (or in-vivo) studies. Clinical studies can be subdivided using different criteria, e.g. using the time aspect, i.e. retrospective or prospective, the data collection process, i.e. cross-sectional or longitudinal, or the characteristics of the study, i.e. observational or experimental. The clinical relevance of any type of study is only one of the factors to be considered. The other crucial question is how sure can we be that the study describes the truth? Scientific standards set rigorous rules for how the study is carried out – the internal validity – as well as to what extent conclusions can be drawn from the findings, depending on the study design – the external validity. Certain minimum criteria need

351

Sackett et al., Editorial. EBM 1995;1:4

352 Case reports

Cross sectional studies

Case-control studies

IV. Expert committee reports Cohort studies or opinions and/or clinical experience of respected authorities

(IV) ...someone once Opinions of respected authorities based on clinical told me evidence, descriptive studies or reports of expert consensus committees

Well-designed experimental studies from more than one centre or research group

(III) respected authorities, Published well-designed trials without randomiexpert committees sation, single group pre-post, (consensus)etc. cohort, time series or matched case controlled studies

RCT with non-definite results (i.e. a point estimate that suggests a clinically significant effect, but with CI overlapping the threshold for this effect)

III. Well-designed nonexperimental descriptive studies, such as comparative studies, correlation studies and case-control studies.

(II-1) Based on a cohort study. (II-2) Based on a case controlled study. (II-3) Based on a dramatic uncontrolled experiment.

At least one published properly designed randomised controlled trial of appropriate size and in an appropriate clinical setting

RCT with definite results (i.e. result with CI that do not overlap the threshold clinically significant effect)

IIa. At least one welldesigned controlled study without randomisation IIb. At least one other quasi-experimental study

5. Expert opinion without explicit critical appraisal, or based on physiology, bench research or “first principles”

4. Case-series (and poor quality cohort and casecontrol studies)

3a. Systematic review (with homogeneity) of case-control studies 3b. Individual case-control study

2a. Systematic review (with homogeneity) of cohort studies 2b. Individual cohort study (including low quality RCT; e.g., <80% follow-up) 2c. “Outcome” research

CEBM Oxford, 1998 http://cebm.jr2.ox.ac.uk/ docs/levels.html 1a. Systematic review (with (I-1) Based on 2 or better At least one published homogeneity of RCTs systematic review of multiple designed randomised 1b. Individual RCT (with controlled trials (RCT), well designed randomised meta-analyses, or systematic narrow confidence interval) controlled trials 1c. All or none reviews. (I-2) Based on a RCT

EBM Working Group, Richards & Lawrence, Br McMaster University 1993 Dent J 1995;175:270

Systematic reviews and Ia. Meta-analysis of randomised controlled trials meta-analyses Ib. At least one randomised controlled trial

US Agency of Health Care Policy & Research 1992

Table 5. Type and strength of evidence of treatment effects

Table 6. Checklist for critical appraisal of papers reporting interventions – e.g. therapy, prevention or aetiology. (adapted from Sackett et al.4) Are the results of the trial valid? 1. Did the trial address a clearly focussed issue?

Yes

Can’t tell

2. Was the assignment of patients to the intervention randomised?

Yes

Can’t tell

3. Were all the patients who entered the trial properly accounted for at its conclusion?

Yes

Can’t tell

Yes

Can’t tell

Yes

Can’t tell

Yes

Can’t tell

Yes

Can’t tell

Yes

Can’t tell

Yes

Can’t tell

An issue can be focused in terms of - the population studied -the intervention -the outcome considered

- was follow-up complete? - were patients analysed in the groups to which they were randomised?

4. Were patients, health workers and study study personnel blind to the intervention? patients? health workers? study personnel?

5. Were the groups similar at the start of the trial? In terms of other factors that might affect the outcome such as age, sex and social class

6. Aside from the experimental intervention were the groups treated equally? What are the results? 7. How large was the effect of the intervention? Which outcome was measured?

8. How precise was the estimate of the effect of intervention? What were the confidence limits?

Will the results help my patients? 9. Can the results he applied to my patients? Do you think that the patients covered by the trial are similar enough to your population?

10.Were all clinically important outcomes considered? If not, does this affect the decision?

11. Are the benefits worth the harms and costs? This is unlikely to be addressed by the trial but what do you think?

353

to be met in order that study findings can be regarded as good evidence of effectiveness. Some types of clinical questions are best answered by using specific study designs and vice versa (http://cebm.jr2.ox.ac.uk/docs/levels.html). Although there is no exact consensus on what constitutes good and bad evidence, the grading of evidence from different types of studies is almost identical, e.g. for therapy (Table 5). Critical appraisal of scientific papers can be carried out using different strategies. One common method is to use check-lists when reading papers. Check-lists with varying degrees of details can be found in various textbooks. An example of a condensed check-list for assessing papers focussed on therapy, prevention and aetiology is shown in Table 6. Similar check-lists have been made for studies on diagnostic tests, decision analyses, economic analyses, harm, etc. Textbooks in statistics and in analytical epidemiology should be consulted to learn critical appraisal2,24 or correct reporting25 of findings from oneâ&#x20AC;&#x2122;s own clinical practice. Our search resulted in no clinical studies where the patients had been randomised with regard to choice of metal-ceramic versus full-ceramic constructions. We therefore proceeded to appraise the controlled clinical studies in accordance with the list in Table 6. Thus, in this particular search we need to extrapolate findings from other studies, which should meet the criteria listed in Tables 4 and 6. The fewer criteria the studies satisfy, the poorer the chances are that the findings in the study will be valid and reliable. Furthermore, no systematic reviews were identified. Among the review papers, two looked interesting enough to read, and were appraised according to the criteria in Table 1. The studies identified described 1, 3 and 5 years of observation of fixed partial dentures made from In-Ceram, Procera and Empress. 4. Applying the new information in treatment After describing your findings to the patient and discussing the limitations of the findings due to the study design, you agree that a metal-ceramic restoration is the best solution for her. Alternatively, you and the patient agree to find the latest information about metal intolerance, risk of material-related adverse effects, etc. using other criteria for selection of valid and reliable studies with optimal study designs.

Concluding Remarks Our clinical practice should be evidence-based in order to give the best and most upto-date care possible. This can be accomplished by routinely asking ourselves the following questions, and conscientiously applying the answers: Do I usually 354

1 identify and give priority to the clinical, psychological, social and other problem(s), taking into account the patient’s perspective? 2 perform sufficiently competent and complete examinations to establish the likelihood of competing diagnoses? 3 consider additional problems and risk factors that may need opportunistic attention? 4 when necessary, seek evidence (from systematic reviews, guidelines, clinical trials, and other sources) pertaining to problems? 5 assess and take into account the completeness, quality, and strength of the evidence? 6 apply valid and relevant evidence to a particular set of problems in a way that is both scientifically justified and intuitively sensible? 7 present the pros and cons of different options to the patient in a way he can understand and incorporate the patient’s priorities and values into the final recommendation?

References 1. Warren KS, Mosteller F. Doing more good than harm: The evaluation of health care interventions. Ann NY Acad Sci 1993; 703: 1-340. 2. Guyatt GH. Evidence based medicine. Ann Intern Med 1991; 114[Sup. 2]: A-16. 3. Jokstad A, Ørstavik J, Ramstad T. A definition of prosthetic dentistry. Int J Prosthodont 1998; 11: 295-301. 4. Sackett DL, Richardson WS, Rosenberg WM, Haynes RB. Evidence-Based Medicine: How to Practice and Teach EBM. New York: Churchill Livingstone; 1997. 5. Miettinen OS. Evidence in medicine: invited commentary. Can Med Assoc J 1998; 158: 215-21. 6. Jokstad A, Mjör IA, Frazier KB. The teaching of all-ceramic restorations in Scandinavian dental schools: a survey. Acta Odontol Scand 1996; 54: 200-4. 7. Greene GS. The fallacies of clinical success in dentistry. J Oral Med 1976; 31: 52-5. 8. Stephens RG, Kogon SL, Bohay RN. Current trends in guideline development: A cause for concern. J Can Dent Assoc 1996; 62: 151-8. 9. Hakestam U, Glantz E, Söderfeldt B, Glantz PO. What do patients expect from extensive restorative dental treatment? Eur J Prosthodont Restor Dent 1996; 4: 53-7. 10. Kronstrom M, Palmqvist S, Eriksson T, Söderfeldt B, Carlsson GE . Practice profile differences among Swedish dentists. A questionnaire study with special reference to prosthodontics. Acta Odontol Scand 1997; 55: 265-9.

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11. Kay EJ, Locker D. A systematic review of the effectiveness of health promotion aimed at improving oral health. Community Dental Health 1998; 15: 132-4. 12. Newsome PRH, Wright GH. A review of patient satisfaction: 1. Concepts of satisfaction. Br Dent J 1999; 186: 166-71. 13. White BA. Use of oral health related quality of life measures in managed dental care organisations. Community Dent Health 1998; 15: 27-31. 14. Creugers NH, Kayser AF. A method to compare cost-effectiveness of dental treatments: adhesive bridges compared to conventional bridges. Community Dent Oral Epidemiol 1992; 20: 280-3. 15. van der Wijk P, Bouma J, van Waas MA, van Oort RP, Rutten FF. The cost of dental implants as compared to that of conventional strategies. Int J Oral Maxillofac Implants 1998; 13: 546-53. 16. Anderson JD. The need for criteria on reporting treatment outcomes. J Prosthet Dent 1998; 79: 49-55. 17. Creugers NH, Mentink AG, Kayser AF. An analysis of durability data on post and core restorations. J Dent 1993; 21: 281-4. 18. Hakestam U, Soderfeldt B, Ryden O, Glantz E, Glantz PO. Dimensions of satisfaction among prosthodontic patients. Eur J Prosthodont Restor Dent 1997; 5: 111-7. 19. Scurria MS, Bader JD, Shugars DA. Meta-analysis of fixed partial denture survival: prostheses and abutments. J Prosthet Dent 1998; 79: 459-64. 20. Creugers NH, Kayser AF, van â&#x20AC;&#x161;t Hof MA. A meta-analysis of durability data on conventional fixed bridges. Community Dent Oral Epidemiol 1994; 22: 448-52. 21. Kreulen CM, Creugers NH, Meijering AC. Meta-analysis of anterior veneer restorations in clinical studies. J Dent 1998; 26: 345-53. 22. Lindh T, Gunne J, Tillberg A, Molin M. A meta-analysis of implants in partial edentulism. Clin Oral Implants Res 1998; 9: 80-90. 23. Brunette DM. Alternative therapies: abuses of scientific method and challenges to dental research. J Prosthet Dent 1998; 80: 605-14. 24. Gray JA. Evidence-based Healthcare. New York: Churchill Livingstone; 1997. 25. Lang TA, Secic M. How to report statistics in medicine. Philadelphia: American College of Physicians, 1997.

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Evidence and the Practice of Prosthodontics: 20 Years after EBD Introduction Alan B. Carr, DMD, MS, FACP Chair, Department of Dental Specialties, Mayo Clinic, Rochester, MN; Division Director, ACP Education & Research, Mentor to ACP Cochrane Oral Health Group, Prosthodontic Practice Network

Keywords Evidence-based dentistry; evidence-based medicine; care outcomes; oral health; health care reform; prosthodontics. Correspondence Alan B. Carr, Department of Dental Specialties, Mayo Clinic, 200 1st St SW, Rochester, MN 55905. E-mail: carr.alan@mayo.edu The author denies any conflicts of interest. Accepted July 30, 2014 doi: 10.1111/jopr.12232

Abstract Prosthodontics has a rich history related to the principles embedded in evidence-based health care. This paper reviews the evidence-based prosthodontics activity over the past 3 decades. It also discusses the impact of health care reform on evidence-based medicine as it relates to broader context of care outcomes. Finally, the value associated with an Evidence Stewardship emphasis in prosthodontics is presented. This emphasis suggests that combining evidence from clinical trials with evidence from clinical practice environments best equips clinicians for the management of patients in the future. Adoption of a strategic Evidence Stewardship direction is an extended commitment to change that recognizes health care reform aims and seeks to be an accountable provider group in the broader health care arena. The vision to form a representative network of prosthodontic practitioners that augments a commitment to Cochrane “clinical trial” data demonstrates a responsibility to professional transparency about who we are, adds value for patients and oral health care providers, impacts teachers and students in dental education, and provides a measure of care accountability unique in dentistry.

The history of prosthodontic involvement in evidence-based dentistry (EBD) spans three decades.1 The importance for recognizing and appreciating this history relates to the utility it brings to future knowledge creation; a challenging process in light of knowledge and technology expansion, the speed of change, and the complexity associated with identifying information important to integrate with patient care.2 This paper will review the prosthodontic EB activity since 1993. Additionally, the health care reform impact on evidencebased medicine (EBM) will be discussed as it relates to broader context of care outcomes. Finally, the value associated with an Evidence Stewardship emphasis in prosthodontics will be presented. This emphasis suggests that combining evidence from clinical trials with evidence from clinical practice environments best equips clinicians for the management of patients in the future.3

Pursuit of an improved framework for professional knowledge A problem of tradition and a new beginning4

A collective recognition of the limitations associated with a tradition-based educational foundation for dental/oral health care led to an organized effort in 1989 for prosthodontics to strategically improve the intellectual approach to patient care.4 The remedy for dentistry’s intellectual limitation was identified 12

as a “new science of the art of medicine; the practice of clinical epidemiology” championed by David L. Sackett at the McMaster University Medical School. This decision was made based on the 1986 experience of Dr. James Anderson, a Toronto academic prosthodontist, who participated in this curriculum and recognized the value to our discipline. The strategy to effect change involved training 10 prosthodontic educatorsi for future dissemination of the McMaster EB teaching, aimed first to graduate prosthodontic program directors in North America. The training course content was designed specifically for prosthodontics by McMaster faculty and spanned two 1-week sessions over two consecutive years. The McMaster University medical faculty, Drs. George P. Browman, Gordon H. Guyatt, Mark N. Levine, and Ray Gilbert, used small-group, self-directed, problem-based learning methods5 over the two sessions. The first session, “Workshop on How to Teach the Critical Appraisal of Clinical Evidence,” took place in June 1993 and included eight unit packages: Therapy, Diagnostic Test, Overview, Clinical Measurement, Prognosis, Causation, Quality of Care, and Economic Evaluation. The second session, i The

individuals selected to participate in this program were as follows: Drs James D. Anderson, Alan B. Carr, David A. Felton, Gary R. Goldstein, Rhonda F. Jacob, Patrick M. Lloyd, Brien R. Lang, Glen P. McGivney, Jack D. Preston, and George A. Zarb.

C 2014 by the American College of Prosthodontists Journal of Prosthodontics 24 (2015) 12–16

Carr

“Research Methods Workshop” took place in April 1994 and covered methodological issues faced in preparing a research protocol: the research question, design architecture, selecting the sample and defining the maneuver, outcomes and measurement, and sample size and statistical analysis. Armed with this new EB framework (for understanding the value that defines research we should be consuming to apply to patients, as well as methods to employ when designing studies aimed at creating new knowledge) the prosthodontic faculty (journal editors and teachers) set out to disseminate what was learned.4

“New evidence-based knowledge” dissemination The strategy for dissemination1 of this new science “innovation” included conducting research symposia sharing the curricula from both McMaster workshops, facilitating the learning needs of the target audience (graduate prosthodontic program directors and their residents), creating learning aids (Critical appraisal user’s guides for dentistry), and encouraging Cochrane Collaboration activity following the establishment of the Cochrane Oral Health Group in 1994. The fundamental EB principles were provided as workshops directed to prosthodontic graduate program directors in 1995 and 1997 (by comparison, the ADA Center for EBD was established in 2007). The curricula included critical appraisal exercises directed at the core clinical research areas of diagnosis, prognosis, harm, therapy, and overview (later termed systematic review), and a discussion of research designs and measurement issues associated with clinical research directed at various clinical questions of interest. The above content was supported by teaching aids for forming a searchable question (PICO), understanding background and foreground questions of learners, the educational prescription, and critically appraised topics (CATs, now termed critical summaries)—all of which can be found at a variety of EB websites.6 To enhance learning of EB principles through dental-specific examples, a series of EB users guide articles were published in 2000 providing dental examples for critical appraisal skills development, clinical research design, and measurement considerations.7 The original publication of user’s guides in medicine began in 1993 and became the core curriculum for teaching and practicing EBM.8 The guides dealing with therapy and diagnosis are presented in two parts: the first part focusing on the validity of an article, the second on an understanding of the results and their application to practice. The harm article deals with interpretation of studies with observational designs, while the prognosis article deals with predicting risk of adverse outcomes. The four topics of therapy, diagnosis, harm, and prognosis represent the core material about primary (original) articles. Integrative articles are those that summarize information from several primary articles. Overviews (currently referred to as systematic reviews) provide the core for all integrative articles, since a systematic review of the available literature is a prerequisite for making treatment recommendations. Commitment to an expectation of acculturation of this new science by future practitioners in prosthodontics is demonstrated by including EB decision-making as a CODA standard.9

Evidence-Based Prosthodontics

Significance of an ACP–COHG alliance Research synthesis

The appropriate assimilation of new clinical information to the management of patients is an increasingly difficult task given the volume and variability of information value. Methods for adding the cumulating knowledge to existing credible knowledge is a process called research synthesis.12 This process, borrowed from the social sciences, led to the establishment of the UK Cochrane Centre in 1992 to continue the maturation of research synthesis applied to health care. The goals of facilitating this work internationally lead to the Cochrane Collaboration beginning in 1993,10 and in 1996 the Cochrane Oral Health Group was established. ACP dual role of better evidence understanding and participating in evidence synthesis

In addition to enhancing our ability to “consume” EB literature for the benefit of patient care, prosthodontic participation in expanding the evidence-generation process through participation in the Cochrane Collaboration is ongoing. To date, several Cochrane Systematic Reviews target prosthodontic topics,11 and the ACP is actively engaged with the Cochrane Oral Health Group (COHG) in enhancing the visibility of and participation with the Cochrane Collaboration within the specialty. Additionally, in 2011 the ACP partnered with the COHG Global Alliance initiative to lead a US effort seeking a more collaborative relationship with the US Dental Specialties Group (DSG) of the ADA. While growing that collaboration continues, the current ACP Strategic Plan includes a continued commitment to grow prosthodontic collaboration with the COHG. ACP–COHG Global Alliance collaboration

The work of the COHG encompasses all providers associated with oral health and consequently encompasses a large, heterogeneous group of topics covering many disciplines aligned with oral, dental and craniofacial diseases and disorders. The Global Alliance seeks to enhance the COHG work through prioritizing topic reviews and providing mechanisms to increase review efficiency.12 Through partnership with the COHG Global Alliance, the ACP can be an active part of discussing content priority for systematic reviews that provide meaning to patient care. The partnership will also facilitate development of prosthodontic clinician researchers with an understanding of the requirements of rigorous clinical study.

Evidence-based penetration in healthcare It is widely agreed that science is cumulative and that the health care enterprise has a responsibility to cumulate scientifically.12 It should come as no surprise that a review of the past two decades defined by the EB paradigm penetration into health care comes with robust and healthy pushback.13-18 Review of the arguments made from both perspectives is helpful to an understanding of the ACP stewardship position.

C 2014 by the American College of Prosthodontists Journal of Prosthodontics 24 (2015) 12–16

Evidence-Based Prosthodontics

Carr

Dissociation through reductionism

It is argued that “through the use of mathematical estimates of the chance of benefit and the risk of harm, derived from high-quality research on population samples expected to inform clinical decision making” the EB process perpetuates the myth that uncertainties and ambiguities will be eliminated.19 This position questions the ability of EB practice to apply to patient management complexity inherent in defining the best thing to do, for an individual patient, at a specific time, and given their unique situation.15 While the twofold premise behind creation of cumulative science in the form of research synthesis was the reduction of biases and imprecision, many expressed concern that the strategies used to accomplish this goal and make sense of disparate information on a similar clinical question are overly reductionist19 and not pragmatic.20

to prosthodontic evidence.26 Quality improvement discussion has encouraged a renewed look at evidence.27 It asks not only for a proper place for evidence from RCTs but also an equal place for pragmatic science—a science of improvement carried out with the “context of care” being a critically important theoretical consideration.28

Evidence Stewardship in prosthodontics

As the gold standard of trial design there have been limitations expressed regarding the use of randomized controlled trials as a proxy for patient management.21 The most common limitations described include restrictive and unrepresentative patient selection, concerns for generalizability of results (patient- and context-related), short-term observation unmatched to chronic conditions, and use of unstandardized outcomes. If such trial characteristics were valid and operational in a pooled estimate of benefit, translation to a general clinical application could yield less precise results than desired. To counter this, the argument is to create the evidence in a more representative context described as a practice-based evidence context.22

The initial purpose for seeking a change in the tradition-based foundation for prosthodontics has been served extremely well since 1993 by the application of EB principles to prosthodontic care. The benefit derived by providers gaining intellectual capacity applicable to patient care provides a meaningful improvement over the tradition-based capacity for knowing the value of published evidence. Additionally, the understanding of experimental methods application to enhance scientific understanding free of bias has been fostered by an EB framework applied to residency training. Despite these benefits, prosthodontics exposure to EB principles has not yet translated to improved evidence to guide care decisions, as demonstrated by the fact that after 20 years there remains limited prosthodontic authorship applied to Cochrane Reviews and insufficient evidence to support basic interventions common to the practice of prosthodontics.29-35 Part of the current challenge relates to a lack of outcome standardization.36 The future challenge relates to an unlikely acceleration of the research enterprise (research groups and funding) supporting oral health-related device and procedural care.37

Health care transformation

Complimentary evidence sources

Important issues impacting health care over the past three decades are useful to consider in the context of this EB evolution and Evidence Stewardship discussion. The Institute of Medicine (IOM) Quality Chasm report made evident the US health care quality-cost mismatch.23 Quality improvement as part of enhancing the value of the care provided became championed. To address health care costs, given the unsustainable care delivery system characterized in IOM and other reports, accountability for quality outcomes and affordable care were being emphasized. This is seen in the Patient Protection and Affordability Care Act (PP&ACA) focus on the Triple Aim of reform.24 The evidence felt most impactful to this value care equationii included patient-centered and affordable quality improvement features. The importance of considering patient preferences and values in the reforming environment was emphasized by the PP&ACA establishing the Patient Centered Outcomes Research Institute (PCORI).25 PCORI places importance on understanding important characteristics of care that are meaningful to patient decision making. Answers to basic questions regarding care emphasized by PCORI have direct application

In light of this situation, and in line with a position of evidence stewardship for patients seeking prosthodontic care, strong consideration for practice-based (PB) evidence creation becomes an important compliment to EB trial information. The complimentary relationship stems from recognizing the importance of the least-emphasized category of the EB five-step process,iii which involves a mechanism that allows recognizing when care falls short of desired outcomes or expectations and requires a provider to “evaluate your performance.”38 It is the recognition of a gap in knowledge or an undesirable care result that leads the provider to seek evidence.

RCT as a proxy for patient management

ii Where value is composed of quality care outcomes delivered safely within

an affordable patient–centric care experience (and for chronic care, within a context of time).

Monitoring of care outcomes

Formalized processes for monitoring oral care outcomes from practice environments are beginning to be discussed.32 Such a process would be aligned with an accountability position in health care,39 support meaningful use of electronic dental records,40 and fuel a shared decision-making interaction with patients that could help address the PCORI emphasis. iii Evidence–based

practice is a five–step process: (1) construct a relevant, answerable question, (2) plan and carry out a search of the literature for the best external evidence, (3) critically appraise the literature for validity and applicability, (4) apply the evidence to your clinical practice, (5) evaluate your performance.

C 2014 by the American College of Prosthodontists Journal of Prosthodontics 24 (2015) 12–16

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Systematically monitoring trial and practice-based prosthodontic evidence positions the specialty to best address pending concerns about value-based41 or accountable care.42 (Value care related to quality outcomes, patient experience, and costs. Delineating the quality outcomes is the work of both the COHG and a network of practicing prosthodontists; delineation of patient experience is best accomplished through practice feedback.) Such evidence will provide a representative body of information that can define the specialty from both clinical trials (Cochrane Global Alliance work) and from our own practices for public awareness use. Being stewards of the evidence pertaining to prosthodonticrelated oral health positions the specialty to contribute to dental education content at undergraduate and graduate levels, collaboration efforts with general practitioners, and the value care discussion through ongoing monitoring of quality care outcomes. Additionally, while the ACP’s past emphasis in defining the specialty has understandably emphasized our training and procedure difference, as evidence stewards, we will have the means to be transparent about the patient care outcome evidence that defines our specialty. (The ACP is the professional association of dentists with advanced specialty training who create optimal oral health, both in function and appearance including dental implants, dentures, veneers, crowns, and tooth whitening.)

Conclusion The current strategic direction chosen by prosthodontics is an extended commitment to change43 that recognizes the health care reform aims, and seeks to be an accountable provider group in the broader health care arena. An April 2008 address by then-secretary Michael O. Leavitt of the USDHHS provides an insightful “market” commentary within the context of a health care message. Secretary Leavitt said, “In a global market there are three ways to approach change. You can fight it and fail; you can accept it and survive; or you can lead it and prosper.”43 The vision to form a network of practitioners representative of prosthodontists that augments a commitment to Cochrane “clinical trial” data demonstrates a responsibility to professional transparency about who we are, adds value for patients and oral health care providers, impacts teachers and students in dental education, and provides a measure of care accountability unique in dentistry.

References 1. ACP Messenger: Prosthodontic research symposium slated. Chicago, American College of Prosthodontists 1994; 24:6 2. Van der Leeuw S, Costanza R, Aulenbach S, et al: Toward an integrated history to guide the future. Ecol Soc 2011;16:2-11 3. Agency for Healthcare Research and Quality: Outcome research. Available at http://www.ahrq.gov/research/findings/factsheets/ outcomes/outfact/index.html. Accessed March 16, 2014 4. Zarb, GA: Prosthodontics 21: a new beginning. J Prosthet Dent 1994;72:23A-24A 5. Neville AJ, Norman GR: PBL in the undergraduate MD program at McMaster University: three iterations in three decades. Acad Med 2007;8:370-374 6. Center for Evidence Based Medicine. Available at http://www. cebm.net/?o=1016 (accessed March 16, 2014)

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7. Journal of Prosthetic Dentistry, Evidence-Based Article Series. Available at http://www.thejpd.org/content/evidencebased. Accessed March 16, 2014 8. Oxman AD, Sackett DL, Guyatt G: Users’ guides to the medical literature. 1. How to get started. The evidence-based working group. J Am Med Assoc 1993;270:2093-2095 9. Commission Dental Accreditation: Accreditation Standards for Advanced Specialty Education Programs in Prosthodontics. Available at http://www.ada.org/˜/media/CODA/Files/prostho. ashx. Accessed August 13, 2014 10. Chalmers I, Hedges LV, Cooper H: A brief history of research synthesis. Eval Health Prof 2002;25:12-37 11. Cochrane Collaboration Oral Health Group: Published Updates, Reviews and Protocols. Available at http://ohg.cochrane.org/ published-updates-reviews-and-protocols. Accessed March 25, 2014 12. COHG Global Alliance. Available at http://ohg.cochrane.org/ga. Accessed March 18, 2014 13. Pincus T: Limitations of randomized controlled trials to depict accurately long-term outcomes in rheumatoid arthritis. Z Rheumatol 1998;57:46-49 14. Feinstein AR, Horwitz RI: Problems in the “Evidence” of “Evidence-based Medicine”. Am J Med 1997;103:529-535 15. Rycroft-Malone J, Seers K, Titchen A, et al: What counts as evidence in evidence-based practice? J Adv Nurs 2004;47: 81-90 16. Berwick DM: Broadening the view of evidence-based medicine. Qual Safe Health Care 2005;14:315-316 17. Horn SD, Gassaway J: Incorporating clinical heterogeneity and patient-reported outcomes for comparative effectiveness research. Medical Care 2012;48:Suppl S17-S22 18. Greenhalgh T: Why do we always end up here? J Prim Health Care 2012;4:92-97 19. Greenhalgh T: Why do we always end up here? Evidence-based medicine’s conceptual cul-de-sacs and some off-road alternative routes. Int J Prosthodont 2013;26:11-15 20. McCormack B, Rycroft-Malone J, Decorby K, et al: A realist review of interventions and strategies to promote evidenceinformed healthcare: a focus on change agency. Implement Sci 2013;8:107 21. Fienstein AR: An additional basic science for clinical medicine: II. The limitations of randomized trials. Ann Intern Med 1983;99:544-550 22. Westfall JM, Mold J, Fagnan L: Practice-based research—“Blue Highways” on the NIH Roadmap. J Am Med Assoc 2007;297:403-406 23. Berwick DM: A user’s manual for the IOM’s ‘Quality Chasm’ report. Health Aff (Millwood) 2002;21:80-90 24. Berwick DM, Nolan TW, Whittington J: The triple aim: care, health, and cost. Health Aff 2008;27:759-769 25. Patient-Centered Outcomes Research Institute home page. Available at http://www.pcori.org/. Accessed March 24, 2014 26. Patient-Centered Outcomes Research Institute: definition of Patient-Centered Outcomes Research. Available at http:// www.pcori.org/research-we-support/pcor/. Accessed March 22, 2014 27. Berwick DA: Broadening the view of evidence based medicine. Qual Saf Health Care 2005;14:315-316 28. Pawson R, Tilley N: Realistic Evaluation. London, Sage, 1997 29. Fedorowicz Z, Nasser M, Wilson N: Adhesively bonded versus non-bonded amalgam restorations for dental caries. Cochrane Database Syst Rev 2009; Oct 7;(4):CD007517. doi: 10.1002/14651858.CD007517.pub2

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30. de Souza RF, de Freitas Oliveira Paranhos H, Lovato da Silva CH, et al: Interventions for cleaning dentures in adults. Cochrane Database Syst Rev 2009; Oct 7;(4):CD007395. doi: 10.1002/14651858.CD007395.pub2 31. Oliver R, Roberts GJ, Hooper L, et al: Antibiotics for the prophylaxis of bacterial endocarditis in dentistry. Cochrane Database Syst Rev 2013; Oct 9;10:CD003813. doi: 10.1002/14651858.CD003813.pub4 32. Innes NP, Ricketts DN, Evans DJ: Preformed metal crowns for decayed primary molar teeth. Cochrane Database Syst Rev 2007; Jan 24;(1):CD005512.pub1 33. Zakrzewska JM, Forssell H, Glenny AM: Interventions for the treatment of burning mouth syndrome. Cochrane Database Syst Rev 2005;1:CD002779 34. Ahangari Z, Nasser M, Mahdian M, et al: Interventions for the management of external root resorption. Cochrane Database Syst Rev 2010; Jun 16;(6):CD008003. doi: 10.1002/14651858.CD008003.pub2 35. de Souza RF, Travess H, Newton T, et al: Interventions for treating traumatised ankylosed permanent front teeth. Cochrane Database Syst Rev 2010; Jan 20;(1):CD007820. doi: 10.1002/14651858.CD007820.pub2 36. Bassi F, Carr AB, Chang TL, et al: Oral rehabilitation outcomes network-ORONet. Int J Prosthodont 2013;26:319-322

37. National Institute of Dental and Craniofacial Research: NIDCR Strategic Plan. Available at http://www.nidcr.nih.gov/research/ ResearchPriorities/StrategicPlan. Accessed August 13, 2014 38. Carr AB, McGivney GP: User’s guide to the dental literature: how to get started. J Prosthet Dent 2000;83:13-20 39. Accountable Care Facts: What is the importance of linking of outcomes measures to payments? Available at http://www. accountablecarefacts.org/topten/what-is-the-importance-oflinking-of-outcomes-measures-to-payments-1. Accessed March 24, 2014 40. Jha AK: Meaningful use of electronic health records. J Am Med Assoc 2010;304:1709-1710 41. Leavitt MO: Building a Value-Based Health Care System. A Prologue Series. Available at http://archive.hhs.gov/secretary/ prologueseries/buildingvaluehc.pdf (accessed March 16, 2014) 42. Cappleaders, America’s Accountable Care Organizations: The top 5 things medical groups can do to prepare for system reform. Available at http://cappleaders.wordpress.com/2012/05/14/ the-top-5-things-medical-groups-can-do-to-prepare-for-systemreform. Accessed March 24, 2014 43. Leavitt MO: Pandemic Flu: Preparedness in a Changing World. Available at http://archive.hhs.gov/secretary/prologueseries/ Pandemic.pdf. Accessed August 28, 2014

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International Journal of Innovation Sciences and Research Available online at http://www.ijisr.com

Vol.5, No, 12, pp. 901-906, December 2016

REVIEW ARTICLE EVIDENCE BASED DENTISTRY IN PROSTHODONTICS *Dr. Deepika Bainiwal, Punjab Government Dental College and Hospital, Amritsar; Punjab Accepted 18th November, 2016; Published Online 30th December, 2016

ABSTRACT Statement of problem: With rapid advancements in dental materials and dental technology and improved understanding of clinical outcomes, a surfeit of research has been published in prosthodontics and dental implant–focused literature. It is well known that not all published literature is scientifically valid and clinically useful. Therefore, a critical analysis of the quality of published research and consolidation of the excess scientific information is necessary to render them significant and useful.  Prosthodontics is a unique speciality that offers numerous merits and demerits for application of principles of evidence based dentistry (EBD).  Evidence based prosthodontics can change the future course of prosthodontics education, clinical research oral health policies that have an impact on prosthodontics and the provision of care to patients.  In the evidence based approach to clinical decision making, dentists incorporate the best scientific evidence—evidence that is critically appraised in systematic reviews—with clinical experience and their patients’ preferences for treatment outcomes. The dental profession should define clinically relevant questions, commission systematic reviews to answer those questions and, when evidence is not available, advocate for good-quality clinical research to be conducted to provide the answers.  (EBD) takes a systematic approach to summarize the large volume of literature that health care providers need to assimilate into their practices. Key words: Evidence based dentistry, Prosthodontics, Levels of evidence.

INTRODUCTION Evidence-based dentistry is the integration and interpretation of the available current research evidence, combined with personal experience. The term ‘evidence-based medicine’, from which evidence-based dentistry has followed, is relatively new (it first became current in the early 1990s) but the core principles that underlie the subject have been in place for many decades in the areas of epidemiology and public health (Hackshaw, 2007). According to the American Dental Association (ADA), EBD is defined as “an approach to oral healthcare that requires the judicious integration of systematic assessments of clinically relevant scientific evidence, relating to the patient’s oral and medical condition and history, with the dentist’s clinical expertise and the patient’s treatment needs and preferences (ADA, 2012).” Therefore, the EBD process is not a rigid methodologic evaluation of scientific evidence that dictates what practitioners should or should not do but also relies on the role of individual professional judgment and patient preference in this process (http://www.ada.org/1754). Evidence dentistry has two main goals- Best evidence/ Research and the transfer of this in practical use. This involves four basic phases; Asking evidence based questions (framing an answerable question from a clinical problem); Search for the best evidence, Reviewing and critically appraising the evidence, Applying this information in a way to help the clinical practice. *Corresponding author: Dr. Deepika Bainiwal, Punjab Government Dental College and Hospital, Amritsar; Punjab

Epidemiological Background The epidemiologic background for evidence-based practice dates back to the nineteenth century, to the work of John Snow, who is widely regarded as the father of modern epidemiology (http://www.ph.ucla). Need to study evidence based prosthodontics Graduates from dental schools are up to date with the best practice in dentistry current at the time they graduate. Some of this knowledge gradually becomes out of date as new information and technology appear. It is important, especially with regards to patient safety, for dentists to be able to keep up to date with developments in diagnosis, prevention and treatment of oral disease, and newly discovered causes of disease (Hackshaw, 2007). In an extensive analysis of scientific publications between 1966 and 2005, Harwood (Harwood, 2008), noted that there were 44,338 published articles in prosthodontics. Of these, there were 955 randomized controlled clinical trials (RCTs) (2%). Nishimura & colleagues (Nishimura et al., 2002) identified 10,258 articles on prosthodontic topics between 1990 and 1999 and estimated that to stay current in the year 2002 would require reading and absorbing approximately 8 articles per week, 52 weeks per year, and across 60 different journals. These numbers do not include published articles on implant dentistry. Russo and colleagues (Russo, 2007) identified 4655 articles published

International Journal of Innovation Sciences and Research

between 1989 and 1999 dedicated to implant dentistry and estimated that to stay current in the year 2000 would require reading and absorbing approximately 1 to 2 articles per week, 52 weeks per year. It is not difficult to assume that these numbers are significantly higher in the year 2013 and will continue to grow due to increased growth in the number of journals and publications, underscoring the need for computerbased clinical knowledge systems and for clinicians to acquire new skills to use the best available scientific evidence (BASE) (Bidra, 2014) as shown in Fig. 1.

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clinical practices in prosthodontics are all based on “weak evidence.” Additionally, 2 critical elements of importance to prosthodontics that are omitted from the evidence-based pyramid are sample size and duration of a study (Bidra, 2014). Therefore, an alternative approach for prosthodontics literature is suggested. The suggested paradigm involves a horizontal spectrum encompassing 3 stages of evidence— preliminary evidence, substantive evidence, and progressive evidence as shown in Fig-3.

Figure 1. EBD involves integration of best available scientific evidence along with individual clinical expertise and patient treatment needs to provide dental care. The need for evidence-based prosthodontics  Enable the recognition of best available scientific evidence in prosthodontics.  Consolidate the scientific information overload in prosthodontics and related literature.  Scrutinize the scientific basis for existing prosthodontic treatments.  Improve current and future treatments.  Encourage improvement in the quality of clinical research as well as in reporting.  Distinguish and advance the specialty of prosthodontics.

Figure 2. Evidence in medicine has been popularly categorized into 5 hierarchical levels and widely represented as a pyramid with the “weakest/lowest level of evidence” at the base and the “strongest or highest level evidence” at the apex. This model may not be applicable to prosthodontics.

Box 1- Summarizes need for evidence based prosthodontics

New skills required by clinicians to adopt evidence-based prosthodontics  Asking the appropriate research question for a clinical situation of interest.  Acquiring information through efficient scientific literature search.  Appraising the acquired information.  Applying the acquired information to clinical practice, along with individual clinical expertise and patient preferences.  Assessing the results of the applied intervention to optimize the clinical situation. Levels of evidence and prosthodontics Evidence in medicine has been popularly categorized into 5 hierarchical levels and widely represented as a pyramid with the “weakest/lowest level of evidence” at the base and the “strongest or highest level evidence” at the apex as shown in Fig 2. The applicability of this paradigm to prosthodontics is questionable because few articles in prosthodontics comprise RCTs and large cohort studies, implying that most current

Figure 3. The suggested new paradigm involves a horizontal spectrum encompassing 3 stages of evidence—preliminary evidence, substantive evidence, and progressive evidence.

Preliminary Evidence Expert/experience-based opinions, philosophies, theories, and biologic plausibilites Expert opinions, philosophies, theories, and biologic plausibilities are all important, because they provide a starting point to initiate and propel new ideas, theories, and innovations and develop further research. Unfortunately, many expert opinions are biased and scientifically not validated. As a result, several popular opinions and philosophies in prosthodontics have not been clinically validated. Some examples include need for balanced occlusion in complete dentures, designs for removable partial dentures, tooth preparation designs, types of restorations in fixed prosthodontics, and many others. Laboratory studies and animal studies In prosthodontics, due to rapid emergence and advancements of new dental materials, dental technology, and improved

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biologic understanding, these studies are important because they provide a good foundation before proceeding with clinical studies. Pioneering work on osseointegration done by PI Branemark in his animal/laboratory studies and its subsequent development through progressive research is a testimony for this type of preliminary research. Case reports and case series They have high sensitivity for detecting novelty and form the basis for detecting new concepts, etiologic clues, side effects, and new treatments and have contributed to major breakthroughs in medicine (Bidra, 2011). In prosthodontic literature, case reports/series typically depict management of unique situations through unique techniques and/or unique materials. Such reports not only help clinicians in management of similar situations but also aid in laying the foundation for future laboratory studies and clinical trials. Substantive Evidence Cross-sectional studies/surveys and descriptive studies A cross-sectional study is defined as a study measuring the distribution of some characteristic(s) in a population at a particular point in time (The Cochrane Collaboration, 2012). Essentially, the exposure and outcome are measured simultaneously, at the time of the survey. An example in prosthodontics is a cross-sectional study to analyze the prevalence of halitosis in patients with fixed complete dentures. In this example, because there is no temporal assessment, it is difficult to conclude that halitosis is related to fixed complete dentures. However, if significant numbers of samples are from a certain social or ethnic background, have a history of smoking or poor oral hygiene, then the researcher can investigate further to delineate the risk factors. Descriptive studies are studies that describe a particular characteristic and any related changes due to an intervention. They are commonly reported in prosthodontics with respect to anatomic variations and esthetic-related characteristics. Therefore, temporal considerations, cause-effect analysis, and survival outcomes are usually not applicable to such studies, which does not mean that the evidence from these studies is “weak.” Major understanding of complete denture principles and esthetic dentistry has resulted from such studies. These studies are specific to a given population, however, and describe preliminary data or trends that may or may not be extrapolated to different populations. Some descriptive studies, however, have large sample sizes encompassing different countries and races (Owens, 2002). Case-control studies A case-control study is defined as “a study that compares people with a specific disease or outcome of interest (cases) to people from the same population without that disease or outcome (controls), and which seeks to find associations between the outcome and prior exposure to particular risk factors (Owens, 2002).” Case-control studies are not commonly described in the core prosthodontics literature, probably because prosthodontics typically does not deal with diseases and cure but with treatment outcomes. Compared with cohort studies, they are inexpensive and afford potential for large sample sizes. They are often associated with controversies and have a potential for propaganda by the media.

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A popular recent example that is relevant to prosthodontics is a case-control study linking the risk of meningiomas and dental radiographs (Claus, 2012). Cohort studies A cohort is a well-defined group of persons who have had a common experience or exposure and are then followed-up to determine the incidence of new diseases or health events. Therefore, by definition, they have the potential to establish causal relationships between exposure and disease. Some examples of cohort studies with long-term follow-up, which have had a significant impact on prosthodontics, include Tallgren’s 25-year follow-up study on reduction of the residual alveolar ridges in complete denture wearers (Tallgren, 1972) and a 20-year follow-up study by Douglass and colleagues (Douglass, 1993) on cephalometric evaluation of vertical dimension changes in patients wearing complete dentures. Unfortunately, such studies are uncommon because they are expensive, time-consuming, and difficult to execute without a significant loss to follow-up of patients. Therefore, short-term cohort studies have become widely popular in the prosthodontics literature, but they do not have the potential to change clinical practices or provide enough data for confident clinical decision making. Furthermore, many cohort studies in prosthodontics with longer follow-up periods lack adequate sample sizes and do not report a life table (survival) analysis. Progressive Evidence Randomized controlled clinical trials RCT is defined as “an experiment in which two or more interventions, possibly including a control intervention or no intervention, are compared by being randomly allocated to participants (Manhony, 2012).”Because they are interventional/ experimental in nature, they have a high sensitivity to prove causation and also yield quantitative data. They are regarded as the best-known method to minimize/control bias, which is defined as a systematic error or deviation in results or inferences from the truth10. Due to these primary factors, they are often considered to provide the “highest level” of evidence in medicine. Methods of randomization Randomization is defined as “the process of randomly allocating participants into one of the arms of a controlled trial.” Broadly, they can be classified as fixed allocation randomization or adaptive randomization and both methods have inherent advantages and disadvantages. Fixed allocation randomization can involve (1) a simple method, such as use of a random integer table; (2) a block method, involving blocks of integers, symbols, or alphabets (usually blocks of 4, such as ABBA); or (3) a stratified method, involving division of the members of population in homogeneous subgroups before sampling. Adaptive randomization methods include baseline adaptive randomization and response adaptive randomization. They are designed to change the allocation probabilities as the study progresses to accommodate imbalances in numbers of participants or in baseline characteristics between the two groups. They also accommodate the responses of participants to the assigned intervention.

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Another form of allocation that is not truly random is quasi randomization. This entails allocation based on a patient’s medical record number or date of birth or by simply allocating every alternate person. Such methods of allocation are easy to manipulate, leading to a selection bias. Parallel-group trial or crossover trial Parallel-group trial or independent group trial is a popular form of RCT and is defined as “a trial that compares 2 groups of people concurrently, one of which receives the intervention of interest and one of which is a control group. Single-mouth trial or split-mouth trial Single-mouth trials are the popular form of RCT in prosthodontics and involve allocation of 1 treatment of interest per mouth. Split-mouth trials refer to a type of clinical trial comparing 2 or more interventions in which the participants are subjected to random allocation of 1 treatment of half of the mouth and another treatment/no treatment of the second half of the mouth. Depending on the intervention, the mouth can be essentially split into maxilla versus mandible, right versus left, or anterior versus posterior areas. The primary objective of using a split mouth design is to eliminate all components related to differences between subjects from the treatment comparisons and thereby reduce the error variance (noise) of the experiment and obtain a more powerful statistical test (Thompson, 2014). An example of a split-mouth trial in prosthodontics is a comparison between all-ceramic crowns and metal-ceramic crowns between right and left sides of the mandible. Systematic reviews (SR) and meta-analysis of RCTs only SR of the literature is defined as “a review of a clearly formulated question that uses systematic and explicit methods to identify, select, and critically appraise relevant research, and to collect and analyze data from the studies that are included in the review.” A meta-analysis (that is, a review that uses quantitative methods to combine the statistical measures from two or more studies and generates a weighted average of the effect of an intervention, degree of association between a risk factor and a disease, or the accuracy of a diagnostic test). For example in a patient with temporomandibular disorder, An attorney contacted a state dental association seeking advice about a lawsuit filed by a patient against a dentist. The patient was diagnosed several years earlier as having a temporomandibular disorder, or TMD. She had been treated with painkillers and muscle relaxants. However, when she changed jobs and moved to a new city, the patient’s new dentist told her that she needed occlusal adjustment to fix her bite, which was causing the pain in the facial muscles.The patient’s attorney wanted to know whether there was any credible scientific evidence showing that occlusal adjustment could relieve the facial pain that his client had experienced over the years. Searching the National Library of Medicine database through PubMed, a staff dentist at the state dental association found one systematic review of randomized controlled trials evaluating the impact of occlusal adjustments (occlusal splints and occlusal adjustment) on signs and symptoms of TMD (Forssell, 1999). The systematic review found four randomized clinical trials of poor quality, and thereby determined that the current evidence did not support the efficacy of occlusal adjustment in the treatment of TMD.

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Hence, this question remains unanswered, and further research is required before a definitive answer can be reached. The evidence does not support or refute the claims of the patient (Ismail, 2004). Systematic reviews and meta-analysis of observational studies or all clinical studies SRs and meta-analyses of only observational studies or including all clinical studies (both RCTs and observational studies) are widely popular in dentistry as well as in prosthodontics because such reviews are better poised to analyze more studies/ data to answer a given clinical question, in comparison to SRs of only RCTs, where data are scarce. Evidence-based considerations for prosthodontic and dental implant occlusion

removable

Taylor, Wiens & Carr (2005) presented a dental literature with discussions of dental occlusion, occlusal schemes, philosophies, and methods to correct and restore the diseased, worn, or damaged occlusion. Their review focused on some of the ‘‘classic’’ removable prosthodontic literature and the currently available scientific literature involving removable prosthodontic occlusion and dental implant occlusion. The authors reviewed the English peer-reviewed literature prior to 1996 in as comprehensive manner as possible, and material after 1996 was reviewed electronically using MEDLINE and summarized that little scientific evidence supports a direct cause-effect relationship between occlusal factors and deleterious biological outcomes for osseointegrated implants. To the contrary, the limited evidence available at this time supports the position that there is no direct cause-effect relationship between occlusion and disease processes. Evidence supporting specific occlusal theories for removable prostheses is primarily based on expert opinion and in vitro studies. Evidence supporting specific occlusal theories for implant-supported prostheses is based on expert opinion, in vitro studies, and animal studies (Tyalor, 2005). Evidence-based treatment planning for dental implants in fixed prosthodontics Wood & Vermilyea (2004) presented a review with evidencebased guidelines to apply when planning treatment with osseointegrated implants. Peer-reviewed literature published in the English language between 1969 and 2003 was reviewed using Medline and hand searches. Topics reviewed include systemic host factors such as age, gender, various medical conditions, and patient habits, local host factors involving the quantity and quality of bone and soft tissue, presence of present or past infection and occlusion, prosthetic design factors, including the number and arrangement of implants, size and coatings of implants, cantilevers and connections to natural teeth, and methods to improve outcomes of implant treatment in each category. The review demonstrated that there is no systemic factor or habit that is an absolute contraindication to the placement of osseointegrated implants in the adult patient, although cessation of smoking can improve outcome significantly. The most important local patient factor for successful treatment is the quality and quantity of bone available at the implant site. Specific design criteria are provided, including guidelines for spacing of implants, size, materials, occlusion, and fit.

International Journal of Innovation Sciences and Research

Limitations in the current body of knowledge are identified, and directions for future research are suggested (Wood, 2004). Guidelines for reporting evidence With the burgeoning publication growth in prosthodontics, it is necessary for investigators to comply with certain guidelines for reporting scientific evidence. The common goal of all guidelines is to improve scientific reporting and ensure standardization so that they allow an accurate assessment of the presented evidence. Popular guidelines are  Consolidated Standards of Reporting Trials (CONSORT) (Schulz, 2010) 1996  Meta-analysis of Observational Studies in Epidemiology (MOOSE) (Stroup, 2008) 1997  Transparent Reporting of Evaluations with Nonrandomized Design (TREND) (Des Jarlais, 2004) 2003  Strength of Recommendation Taxonomy (SORT) (Ebell, 2004) 2004  Assessment of Multiple Systematic Reviews (AMSTAR) (Shea, 2007) 2007  Preferred Reporting Items for Systematic Reviews and Meta- Analyses (PRISMA) (Moher, 2009) 2007 Limitations of evidence based prosthodontics  Applicability of research to a specific patient population, publication biases, paucity of current data, cost, and ethics.  Information gained from clinical research may not directly answer the principal clinical question of what is best for a specific patient. This is because it is acknowledged that the homogeneity and characteristics of patients participating in clinical trials may be significantly different from those seen in dental offices.  EBD does not provide a cookbook that dentists must follow nor does it establish a standard of care (Bidra, 2014). Conclusion A primary advantage of the evidence-based practice model is that it provides the least-biased, best-validated information on which to base decisions. However, the available scientific evidence for many aspects of clinical dentistry is either weak or nonexistent. This presents the dental profession with a major hurdle as it begins to implement an evidence-based model of clinical practice. Although some have questioned the rationale for EBD and the opportunities associated with this approach, it is clear that the evidence-based approach raises questions about how the dental knowledge base has been incorporated into dentistry, both in dental education and clinical practice. Presenting selective evidence in teaching and practice can lead to biased decisions, but if the methods of EBD are followed appropriately, there is less potential for bias by researchers, academicians and other experts.

REFERENCES ADA Center for Evidence-Based Dentistry. Available at: http://ebd.ada.org/about. aspx. Accessed December1, 2012.

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ADA Policy on Evidence-Based Dentistry. Available at: http://www.ada.org/1754. aspx. Accessed December 1, 2012. Bidra AS, Uribe F. Successful bleaching of teeth with dentinogenesis imperfect discoloration: a case report. J Esthet Restor Dent 2011; 23(1):3–10. Bidra, AS. Evidence based prosthodontics; Fundamental considerations, Limitations and Guidelines. Dent Clin N Am 2014; 58:1-17. Claus EB, Calvocoressi L, Bondy ML, et al. Dental x-rays and risk of meningioma. Cancer 2012; 118(18):4530–7. Des Jarlais DC, Lyles C, Crepaz N, TREND Group. Improving the reporting quality of nonrandomized evaluations of behavioral and public health interventions: the TREND statement. Am J Public Health 2004; 94(3):361–6. Douglass JB, Meader L, Kaplan A, et al. Cephalometric evaluation of the changes in patients wearing complete dentures: a 20-year study. J Prosthet Dent 1993; 69(3):270– 5. Ebell MH, Siwek J, Weiss BD, et al. Strength of recommendation taxonomy (SORT): a patient-centered approach to grading evidence in the medical literature. Am Fam Physician 2004; 69(3):548–56. Forssell H, Kalso E, Koskela P, Vehmanen R, Puukka P, Alanen P. Occlusal treatments in temporomandibular disorders: a qualitative systematic review of randomized controlled trials. Pain 1999;83: 549-60. Hackshaw A, Paul E, Davenport E. Evidence based dentistryAn introduction. Blackwell Munksgaard 2007. Harwood CL.The evidence base for current practices in prosthodontics. Eur J Prosthodont Restor Dent 2008; 16(1):24–34. Hujoel PP, DeRouen TA. Validity issues in split-mouth trials. J Clin Periodontol 1992; 19(9 Pt 1):625 7. Ismail AI, Bader JD. Evidence-based dentistry in clinical practice. JADA, Vol. 135, January 2004; 78-83. Moher D, Liberati A, Tetzlaff J, PRISMA Group. Preferred reporting items for systematic reviews and meta-analyses: the PRISMA statement. J Clin Epidemiol 2009;62:1006– 12. Nishimura K, Rasool F, Ferguson MB, et al. Benchmarking the clinical prosthetic dental literature on MEDLINE. J Prosthet Dent 2002;88(5):533–41. Owens EG, Goodacre CJ, Loh PL, et al. A multicenter interracial study of facial appearance. Part 1: a comparison of extraoral parameters. Int J Prosthodont 2002; 15(3):273– 82. Russo SP, Fiorellini JP, Weber HP, et al. Benchmarking the dental implant evidence on MEDLINE. Int J Oral Maxillofac Implants 2000; 15(6):792–800. Schulz KF, Altman DG, Moher D, CONSORT Group. CONSORT 2010 statement: updated guidelines for reporting parallel group randomised trials. J Clin Epidemiol 2010; 63: 834–40. Shea BJ, Grimshaw JM, Wells GA, et al. Development of AMSTAR: a measurement tool to assess the methodological quality of systematic reviews. BMC Med Res Methodol 2007; 7:10. Stroup DF, Berlin JA, Morton SC, et al. Meta-analysis of observational studies in epidemiology: a proposal for reporting. Meta-analysis Of Observational Studies in Epidemiology (MOOSE) group. JAMA 2000; 283(15):2008–12. Tallgren A. The continuing reduction of the residual alveolar ridges in complete denture wearers: a mixed-longitudinal

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study covering 25 years. J Prosthet Dent 1972; 27(2):120â&#x20AC;&#x201C; 32. The Cochrane Collaboration. Glossary of Terms. Available at: http://www. cochrane.org/glossary. Accessed December 1, 2012. Tyalor TD, Weins J, Carr A. Evidence-based considerations for removable prosthodontic and dental implant occlusion: A literature review. (J Prosthet Dent 2005; 94: 555-60.)

UCLA Department of Epidemiology. John Snow. Available at: http://www.ph.ucla. edu/epi/snow.html. Accessed December 1, 2012. Wood MR, Vermilyea SG. A review of selected dental literature on evidence-based treatment planning for dental implants: Report of the Committee on Research in Fixed Prosthodontics of the Academy of Fixed Prosthodontics J Prosthet Dent 2004; 92: 447-62

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Implant Prosthodontics Oreste Iocca, Giuseppe Bianco, and Simón Pardiñas López

Abstract

The goal of a prosthetic restoration is to provide good esthetic and functional outcomes on a long-term basis. For the clinician, implant prosthodontics poses many decision-making challenges. Choice of screw- or cement-retained implant prosthesis is still a matter of personal preference, although some specific indications and contraindications are retrievable from the literature. Ease of manufacturing, risk of complications, cost, and chair time are all factors that need to be evaluated in the choice of a retention system. Another doubt may arise regarding the adoption of cantilever prosthesis in place of more complex surgical or prosthetic options. Finite element analysis studies and clinical trials may help in providing survival and complication rates of cantilevers. In selected cases, advanced treatment options are necessary. It is the case of zygomatic implants, which are useful when more traditional approaches are unfeasible. Considering the delicate structures involved and the surgical skills required, placement and restoration of zygoma implants should be performed in adequate structures by properly trained clinicians. The All-on-FourTM is a prosthetic concept which employs four implants in the anterior jaw, of which the distal two are maximally angulated. The sparse evidence coming from the literature suggests that this can be a reliable option in selected cases.

O. Iocca, DDS ( ) International Medical School, Sapienza University of Rome, Viale Regina Elena 324, 00161 Rome, Italy

G. Bianco, DDS, PhD Centro Polispecialistico Fisioeuropa, Viale dell’Umanesimo, 308, Rome 00144, Italy e-mail: gbianco@mac.com

Private Practice Limited to Oral Surgery, Periodontology and Implant Dentistry, Rome, Italy e-mail: oi243@nyu.edu

S. Pardiñas López, DDS, MS Oral Surgery, Periodontology and Implantology, Clínica Pardiñas, A Coruña, Galicia 15003, Spain e-mail: simonplz@hotmail.com

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Another question that seeks for an answer regards the ideal number of implants to achieve optimal results. Clear indications are available for fullmouth fixed rehabilitations, in which minimum four implants in the mandible and six implants in the maxilla are considered the most reliable solutions. Implant overdentures are still an important option for edentulous patients, especially in the elderly. Analysis of the various attachment systems and the number of implants can help in selection of the best treatment options. Accurate impression taking is a fundamental step for achievement of optimal prosthetic results. Materials adopted should possess some fundamental basic properties. Regarding the impression techniques in implant dentistry, two options are available: transfer and pick up. Finally, optimal esthetic results depend by numerous factors; it is the mimicry with the natural tissues that ensures the best outcomes. It is not easy to arrive at strong evidence-based conclusions on this topic, mainly due to the lack of RCTs and a poorly standardized way of reporting the esthetic outcomes.

9.1

Prosthetic Options in Implant-Fixed Prosthodontics

9.1.1

Cement-Retained Versus Screw-Retained Implant Reconstructions

Retention systems for implant prostheses can be obtained via screw retaining or through cementation. These two options gave distinct advantages and disadvantages in clinical practice, but doubts still exist if the choice of a retention system over another can give some improvement in terms of success and survival rates (Tables 9.1 and 9.2). The choice one of the alternatives is still a matter of personal preference for many clinicians; therefore, an evidence-based approach should elucidate which are the main indications and problems of the two fixation methods in order to facilitate decision-making in the everyday practice (Fig. 9.1). Sailer and coll. [1] systematically reviewed the survival and complication rates of cemented and screw-retained reconstructions, providing summary estimates at 5 years. The analysis

included RCTs, prospective and retrospective studies on single crowns, FDPs, and full-arch restorations. Regarding implant survival, no difference was found for single crowns between cement-retained and screw-retained groups, although for FDPs and full-arch prostheses, the incidence of implant loss appeared to be higher for cemented reconstructions. This is in line with precedent observations: cemented reconstructions are associated with a variable amount of cement excess around

Table 9.1 Screw-retained restorations Advantages Ease of retrievability

Decreased risk of biological complications because of the absence of cement Possibility of restoration even with limited crown space

Disadvantages Impossibility of placing a screw when the position of the screw-access hole lies on the incisal margin in case of excessively angulated implants Slightly larger bulk of the prosthesis framework compared to cement retained; this is due to the necessity of accommodate the screwaccess hole

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the implant which is the cause of inflammation and implant loss in some cases. When survival of the prostheses was analyzed, in single-crown study, more reconstructions failed in the screw-retained group. Also the fullarch prostheses group showed a similar trend with higher reconstruction failures in the screw group. Anyway, these results were not statistically significant. Table 9.2 Cement-retained restorations Advantages A general ease of manufacturing and manipulation, due to their similarity with reconstructions on natural abutments Reduced cost and less chair time

Disadvantages Difficulty in removal of excess cement, which is one of the main causes of biological complications

Difficult removal of the restoration if the abutment screw loosens Considering that cemented prostheses necessitate at least 5 mm to provide retention; in case of reduced occlusal space, adoption of a screw-retained restoration is the only choice

Fig. 9.1 This is a typical case in which an angulated abutment is necessary due to the bone anatomy; this situation usually occurs in the anterior regions. The use of a screwretained restoration will result in an access hole on the buccal aspect (red line), which is contraindicated in the esthetic zone. For this reason, a cemented restoration is preferable

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On the opposite side, FDPs showed a trend suggestive of greater prosthetic failure rates for the cemented group, but again results were not statistically significant. The analysis outlined that technical complications were generally higher for the screw-retained reconstructions, in particular screw loosening and chipping/fracture of the ceramic. Regarding this last complication, one may ask why cemented prostheses suffer a lesser degree of ceramic damage; it is likely that the occlusal forces exerted on the cemented restoration simply lead to decementation. Oppositely, when forces are exerted on screw-retained prostheses, they are not dissipated, and consequently their full load acts on the ceramic, unless screw loosening occurs. As expected, serious biological complications (bone loss exceeding 2 mm) were more frequent for cement-retained reconstructions; this is in line with the numerous studies about the incidence of peri-implantitis due to excess of cement around the implants. It is also expected that access to cement remnants is impaired with large reconstructions; this may explain the higher failure rates of implants under cement-retained restorations. Technical complications were higher for the screw-retained group, the most frequent being loosening of the screw. It must be addressed that complications of this kind, although timeconsuming and unpleasant for the patient, are usually resolvable within a single visit. On the opposite side, if the abutment screw loosens under cemented restorations, retightening of the abutment screw may become difficult/impossible and destruction of crown necessary in order to uncover the screw hole. In the end, the authors concluded that cemented reconstructions exhibit less technical complications but more serious biological problems reflected in higher implant failure rates. Specifically, for single crowns, incidence of complications was similar for both groups; therefore, both types of fixation methods can be recommended (Figs. 9.2 and 9.3), but when FDPs and full-arch restorations are employed, screwretained reconstructions seem preferable for the

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ease of retrievability and for the lower rates of biological problems (Fig. 9.4). Another systematic review [2] analyzed the survival rates according to material type and type of reconstruction, giving estimates at 5 years.

Failure rates by reconstruction type put in evidence a not statistically significant higher survival for cement retained when compared to screw-retained single crowns, FDPs, and fullarch restorations.

Fig. 9.2 Example of cemented restoration in the molar region; this is a case in which the choice of the retention system is a matter of clinicianâ&#x20AC;&#x2122;s personal preferences.

A screw-retained restoration would have been feasible without contraindications

Fig. 9.3 Example of screw-retained restoration in the molar region (a, b)

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Fig. 9.4 (aâ&#x20AC;&#x201C;c) Example of screw-retained restoration for a three-unit implant prosthesis

When abutment material was analyzed, neither cemented nor screw-retained reconstructions showed a statistically significant difference with the different materials employed. Same result was obtained analyzing different prosthetic and cement materials.

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Regarding the technical complications, a statistically significant difference was confirmed between the two groups. In particular, loss of retention and ceramic chipping/fracture were higher for the screw-retained group. Specifically for the cemented group, an interesting comparison between the type of cement adopted and the loss of retention was performed. It showed the ZOE cements perform better than resin and glass ionomer. Biological complications were significantly higher for the cement group, further strengthening the assumption that cement residues are one of the main causes of peri-implantitis and implant loss. The authors draw the conclusion that the higher risk of implant loss and the limited possibility of reintervention after definitive cementation should lead to propension toward screw-retained restorations. The review of Chaar and coll. [3] focused on cement-retained restorations only, subdividing the analysis in long-term (1â&#x20AC;&#x201C;5 years of f-up) and short-term studies (>5 years of f-up). As expected, more technical complications were reported in long-term studies. Incidence of abutment screw loosening amounted to up to 4.3 % for the shortterm and up to 10 % for long-term studies. An interesting observation was that more recent studies showed lesser incidence of abutment screw loosening, likely because of the improvement in manufacture and mechanical characteristics of implant components. Loss of retention was the most common technical complication; the type of cement used can improve the clinical results, but controversies still exist on this matter. Zinc phosphate ensures the highest retention, but on the other hand provisional cements such as ZOE may work properly and at the same time provide retrievability if needed. At the end, reliability of cement-retained single-crown restorations was deemed similar to screw retained. But the author concluded that for long-span FDP and full-arch restorations, the adoption of cement-retained restorations is not recommended.

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An analysis on MBL changes around implant cement- or screw-retained restorations was performed by de Brandao and coll. [4]. Only two studies, out of a total of the nine included, were found to directly compare the two groups; the others described cement-retained and screwretained MBL separately. Follow-up was in the range of 12–48 months. The pooled mean periimplant marginal bone loss for the screw group was 0.89 mm (0.44–1.33), and for Cement group, it was 0.53 mm (0.31–0.76); this difference was not deemed statistically significant. It must be noted that the results might be biased by the fact that the majority of comparisons were not direct but instead an extrapolation from studies performed for other kind of evaluation. Moreover, it should be recalled that MBL may be influenced by many other factors than retention systems, such as smoking habits, poor oral hygiene, etc., and it is not known to what extent each one may have a preponderant role (Tables 9.3, 9.4, 9.5, and 9.6).

9.1.2

Cantilevers for ImplantSupported Prostheses

In some situations such as bone atrophy or the need of avoiding damage to anatomical structures (e.g., maxillary sinus, mental foramen), insertion of implants becomes possible only with more complicated implant treatment options; these may consist of bone augmentation procedures, use of short implants, or placing angulated implants. When all these alternatives cannot be employed or are excluded for any reason, a cantilever can be adopted [5]. A cantilever prosthesis is defined as a free-end extension retained by natural or implant abutments (Figs. 9.5 and 9.6). Due to the particular design of this solution, i.e., a first-class lever, it was a matter of debate if the use of cantilevers could be the cause of excessive load over the supporting implants and if such design could lead to increased rates of complications such as framework fractures.

Table 9.3 Summary of the systematic reviews providing a quantitative analysis of reconstruction survival rates for screw-retained and cement-retained groups

Sailer and coll. [1] 5-year estimate 95 % CI Wittneben and coll. 10-year estimate 95 % CI

Screwretained single crown 89.3 % (64.9–97.1)

Cementretained single crown 96.5 % (94.8–97.7)

Screwretained FPD 98.0 % (96.2–99.0)

91.1 % (76.7–96.8)

96.3 % (93.9–97.8)

91.5 (%76.5– 97.1)

Cementretained FDP 96.9 % (90.8–99.0)

Screw-retained full-arch restoration 95.8 % (91–97.9)

Cement-retained full-arch restoration 100 % (88.9–100)

94.6 % (85.8–98.1)

96.7 % (93.6–98.3)

Table 9.4 Summary of the systematic review providing a quantitative analysis of implant survival rates for screwretained and cement-retained groups

Sailer and coll. [1] 5-year estimate 95 % CI

Screwretained single crown 98.6 % (96.6–99.4)

Cementretained single crown 97.7 % (96.8–98.4)

Screwretained FPD 98.7 % (97.6–99.3)

Cementretained FDP 97.6 % (96.8–98.3)

Screw-retained full-arch restoration 98.4 % (95.8–99.4)

Cement-retained full-arch restoration 94.2 % (86.5–97.6)

Cement-retained single crown Abutment screw loosening 3.9 % (2.8–5.4) Chipping 2.8 % (1.4–5.5) Abutment screw fracture 0.4 % (0.1–1.8) Screw-retained FPD Chipping 13.3 % (8.4–20.7) Screw loosening 11.0 % (7.2–16.7) Screw fracture 3.8 % (1.7–8.4)

Cement-retained FDP Chipping 24.9 % (6.5–70.7) Screw fracture 0.0 % (0–5.6) Screw loosening 0.0 % (0–5.1)

Screw-retained full-arch restoration Chipping 23.3 % (16.1–33.0) Screw loosening 9.4 % (3.1–26.6) Screw fracture 6.6 % (1.7–24.5)

Cement-retained full-arch restoration Chipping 67.4 % (49.9–83.7) Screw loosening 3.1 % (1.5–6.4) Screw fracture 0.0 % (0–37.7)

Sailer and coll. [1] 5-year estimate 95 % CI

Screw-retained single crown Soft tissue complication 23.9 % (14–39.1) Soft tissue recession 0.0 % (0–36.9) Bone loss >2 mm 0.0 % (0–6.0)

Cement-retained single crown Soft tissue recession 4.4 % (1.0–17.6) Soft tissue complication 4.3 % (3.0–6.1) Bone loss >2 mm 2.8 % (1.3–6) Screw-retained FPD Soft tissue complication 6.5 % (2–20) Bone loss >2 mm 2.5 % (2.3–4.7) Soft tissue recession (Na)

Cement-retained FDP Bone loss >2 mm 6.5 % (4.6–9.1) Soft tissue recession 0.0 % (0–49.5) Soft tissue complication (Na)

Screw-retained full-arch restoration Soft tissue recession 16.7 % (11.8–23.9) Bone loss >2 mm 11.4 % (6.7–18.9) Soft tissue complication (Na)

Cement-retained full-arch restoration Bone loss >2 mm 34.7 % (18.5–54.3) Soft tissue complication (Na) Soft tissue recession (Na)

Table 9.6 Summary of the systematic review providing a quantitative analysis of biological complication rates for screw-retained and cement-retained groups

Sailer and coll. [1] 5-year estimate 95 % CI

Screw-retained single crown Screw loosening 21.2 % (14.4–30.4) Chipping 9.6 % (2.5–33.8) Screw fracture (none)

Table 9.5 Summary of the systematic review providing a quantitative analysis of technical complication rates for screw-retained and cement-retained groups

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Fig. 9.6 Example of distal cantilevers in a full-mouth restoration. This can be considered a predictable solution although no strong evidence in this regard is available yet

Fig. 9.5 (a, b) Example of mesial cantilever retained by three implant abutments. This configuration unlikely will give any problem considered that is the most favorable situation from a biomechanical point of view

Finite element analysis (FEA) tests have attempted to study the stress distribution on bone, implants, and prostheses in the presence of a cantilever. Padhye and coll. [6] simulated a mandible model and six implants supporting a cantilevered fixed prosthesis; the length of the cantilever was simulated at 10, 15, and 20 mm from the distal part of the terminal implant. The distribution of

loads around the peri-implant bone was studied. On application of vertical forces at the most distal point, the results suggested a direct increase of stress on all the components of the simulation every 5 mm increment in cantilever length. It was suggested that implants connected between each other in a rigid manner may help balance the tension developed where the force is exerted. Also, regardless of the cantilever length, the greatest amount of stress was placed around the most distal implant. In order of magnitude, the stress was greatest on the framework, the implant, and the cortical bone and least on the medullary bone. A similar FEA was conducted by Park and coll. [7] for evaluation of stress distribution on a mandibular-cantilevered implant crown subjected to vertical and oblique loads. Vertical forces applied on the cantilever resulted in an increased stress upon the cortical bone which increased linearly in proportion to the distance of the applied load from the center of the crown. Instead, when oblique load was applied lingually at 30Â°, the least amount of stress on the bone and implant occurred when the force was exerted at 5 mm from the center of the crown. While going toward the center the stress increased on the buccal bone, moving toward the lingual side, the stress was greatest on the implant first and on the lingual bone going at a distance of 7 mm. An attempt to simulate the bone remodeling induced by FPD with cantilever extensions was also performed. In the study of Wang and coll. [8], a 3D FEA models of the maxilla were

Implant Prosthodontics

created, and bone remodeling equations were applied establishing a reference stimulus, an overload threshold, a remodeling coefficient for cortical and trabecular bone, and a lazy zone. In this way, it was possible to simulate, within the limits of computer-generated values, how the bone responds to different prosthetic designs. The model gave the results of a more distributed bone density induced by the non-cantilever configuration; the cantilever model resulted in a lower density around the implant neck indicative of increased bone remodeling due to the stress exerted by the loads of the cantilever model. It must be pointed out that FEA studies attempting to evaluate what happens in a given clinical scenario are always a simplification of the real mechanisms occurring in a biological system. Bacterial influence, bone cell response to different stresses, assumption that bone is an isotropic material when in fact it is anisotropic, these are all factors that are difficult or impossible to include in a FEA study. Also, the simulated forces are simplified in respect to what happens in vivo because it is difficult to simulate the patterns of mastication loading. Nevertheless, this kind of studies can help in giving orientations to the clinical research allows to understand some phenomenons difficult to evaluate in real-life situations. Clinical studies on dental implant prosthesis cantilever have been conducted by many groups of research with some conflicting results emerging from the analysis of the literature. These controversies arise because of the high heterogeneity between the various studies and in general because of a paucity of well-performed RCTs. Torrecillas-Martinez and coll. [9] performed a meta-analysis evaluating the marginal bone loss (MBL) and the prosthetic complications of implant-supported cantilevers. Only cohort studies were included with a follow-up range of 3â&#x20AC;&#x201C;8.2 years. The amount of MBL was found to be less for the non-cantilever group, but the results were not statistically significant (p = 0.47). It was pointed out that MBL is anyway influenced by many factors other than the peri-implant

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stress caused by a cantilever extension; therefore, the results should be taken cautiously. Regarding the technical complications, porcelain fracture was the most common, but its relation with the presence of cantilever was not clear; on the other hand, screw loosening for the cantilever group had a relatively higher incidence than the non-cantilever restorations. It was possible to draw the conclusion that MBL does not seem to be related to the cantilever and that only minor prosthetic complications can occur when a distal extension is present. A systematic review [10] of the survival rate and the biological, technical, and esthetic complications of cantilevered implant prostheses with a mean of 5 years of follow-up was performed. Summary estimates at 5â&#x20AC;&#x201C;10 years were calculated by the inclusion of prospective and retrospective studies. Implant survival in implant-supported cantilever prostheses was estimated to be 91.1 % (CI 90.1â&#x20AC;&#x201C;99.2), very similar to previous results on implant prostheses without cantilever extensions (see Chap. 3). The authors also analyzed the componentrelated complications and the prosthesis complication. Cumulative incidence for implant fracture was again similar to other studies on noncantilever restorations. The same was true for veneer fracture. Regarding the biological complications, MBL did not seem to be influenced by the cantilever extension, while the incidence of peri-implantitis was not evaluated for poor reporting in the included studies. In light of this, rehabilitation with a cantilever extension was not considered detrimental in terms of implant survival, complications, and bone loss when compared to non-cantilever group. Similar results were obtained in a systematic review [11] including prospective, retrospective, and case-control studies, in which weighted mean of implant loss was higher for cantilever implant prostheses than non-cantilever group. The most common complication detected was chipping followed by screw loosening, and their

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incidence was slightly higher in the cantilever group. The presence of cantilever seemed to have no effect on significant peri-implant bone loss. In the end, this review further corroborates the assumption that incorporation of cantilever prostheses may be associated with a slight increase in technical complications, but overall, it is safe to say that implant-supported short cantilever extensions may be considered an acceptable treatment option. It seems clear that implant-supported cantilever extension can be considered a predictable and reliable treatment option. On the other hand, it should be noted that no study clearly defined the effect of mesial (Fig. 9.5) versus distal cantilever on the survival and complications rates of implants and prostheses; moreover, studies evaluating single implant cantilevers are scarce. Also, all the systematic reviews and meta-analysis point out that few studies and no RCTs are available, although a positive factor is that heterogeneity between the various studies is considered to be low. Furthermore, numerous biases such as smoking, parafunctional habits, and oral hygiene can confound the results of the biological complications. Within these limitations, the adoption of implant-supported cantilever restorations sup-

ported by two or more implants is a valid option that may be adopted when other, more complicated solutions are excluded from the treatment planning (Table 9.7).

9.1.3

Tilted Implants

The use of tilted implants represents another alternative in treatment of partial or complete edentulism. For example, the use of tilted implants inserted adjacent to the maxillary sinus wall can spare a sinus lift procedure (Fig. 9.7). In the mandible, the excessive bone atrophy of the posterior regions may render the placement of tilted implants in the intraforaminal area the only alternative to a bone grafting procedure. The question is if the angulation of an implant may lead to unfavorable loading conditions and if this is related to worst clinical outcomes compared to axially placed implants. Again, FEA studies may help in addressing the question if, in the presence of tilted implants, stress loads are increased on the bone and on the implant structures. The FEA analysis performed by Bevilacqua and coll. [12] on a 3D edentulous jaw compared axially placed versus tilted implants at various degree of angulation. As expected, loading and

Table 9.7 Systematic reviews evaluating the effect of cantilever on implant-supported prostheses – implant survival

Romeo and coll. [10] 5–10-year estimate 95 % CI Zurdo and coll. [11] Weighted mean 5-year survival 95 % CI Aglietta and coll. [50] Cumulative 5-year estimate 95 % CI

Implant fracture complication 0.7 % (0.1–4.7)

Screw or abutment fracture Veneer fracture complication complication 1.6 % (0.8–3.5) 10.1 % (3.7–16.5 %)

Implant survival 98.7 % (96.2– 99.5)

Prostheses survival 96.5 % (94.8–97.7)

97.1 % (95.5– 98.6)

91.9 % (88–95.8)

97.1 % (94.3– 98.5)

84.1 % (−98)

1.3 % (0.2–8.3)

2.1 % (0.9–5.1) 10.3 % (3.9–26.6)

Biological complications 5.7 % (4.2–7.6)

10.5 % (3.9–26.4)

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tilting single implants increased the stress on the peri-implant bone. An interesting finding was that tilted implants supporting a shortened cantilever decreased the stress on both the bone and the prosthetic structure when compared to vertical implants supporting cantilever prostheses. This suggests that tilted implants may aid in decreasing the stress on the peri-implant bone and prosthesis because they allow a reduction of the cantilever length. A two-dimensional FEA [13] arrived at the same conclusions, showing that although increased loading from the presence of cantilever cannot be eliminated, it is anyway reduced greatly with the inclination of the distal implants. These results encouraged the adoption of tilted implants in clinical studies in order to improve the prosthetic and biological outcomes. Lan and coll. [14] simulated different combinations of angulations (vertical, mesial, or distal inclination) of two adjacent implants supporting a splinted prosthesis. It was found that the loading type (vertical or oblique) is the main factor in determining the stress on the peri-implant bone. Also, the parallelism or divergence of implant apices seemed of not having an influence of bone stress. Furthermore, the distal inclination of one implant and vertical position of the other resulted in peak of maximum stress: therefore, it was suggested to avoid this configuration in clinical practice.

Fig. 9.7 Tilted implant placed in a patient that refused the sinus lift procedure

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Systematic reviews and meta-analysis attempted to draw some conclusions from data retrieved by clinical studies specifically evaluating tilted implants. A recent meta-analysis included 44 publications [15] on this topic, but only retrospective and prospective clinical studies were found, with no presence of RCTs. A positive factor was the low heterogeneity between the included studies. Results showed that there was a not statistically significant difference regarding implant failure rates of tilted implants when compared to vertically placed. The authors performed a subgroup analysis in order to evaluate maxillary and mandibular implants separately; in the maxilla, a significant difference was found favoring the axially placed compared to tilted implants. Conversely, no difference was evidenced for the mandibular implants. This can be explained by the fact that maxillary bone, especially in the posterior regions, is of poor quality and consequently prone to suffer from the higher stress derived by tilted implants. This problem instead seems to not affect the denser mandible. About MBL changes, no significant difference was outlined between the two groups. Two other previous meta-analyses [16, 17] draw similar conclusions, but when subgroup analysis of mandibular and maxillary implants was done, no significant difference between the two was found, probably because in these analyses, studies with longer follow-ups were included (>1 year after loading), and this probably led to equilibrate the success and failures between the maxillary and mandibular groups. A systematic review and meta-analysis addressed the question of immediate loading rehabilitation with tilted implants only of the maxilla [18]. No significant differences were found between axial and tilted groups regarding implant survival and MBL change. Therefore, immediate loading with tilted implants in the maxilla was considered a reliable procedure. Limitations of these reviews and meta-analyses need to be considered. First, no RCTs evaluating the use of angulated implants in the mandible or maxilla were available for inclusion. Obviously, additional long-term studies are necessary. This

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has direct repercussions on the inability to control confounding factors, especially smoking, parafunctional habits, and oral hygiene measures. Moreover, most studies are retrospective, which does not allow to have much control on the study in terms of record of information, missing data, and impossibility to set the participants of the study. Many clinical studies have small sample size and short follow-up period. Finally, there is no consensus in the definition of the minimal angulation that allows to define an implant tilted or axially placed; moreover, it is difficult to standardize the angulation in the various clinical circumstances because this is dictated by the highly variable individual anatomy. Nevertheless, the consistent results in various published reviews and meta-analyses suggest that angulation of dental implants in the mesiodistal plane does not seem to jeopardize the implant

survival and the crestal bone level changes around dental implants (Tables 9.8 and 9.9).

9.1.4

Zygoma Implants

Anchorage of long implants to the zygoma bone is yet another alternative in case of extreme maxillary atrophy. Advantages of zygomatic implants include: • Avoidance of bone grafting or complicated surgical procedures such as Le Fort I osteotomies or distraction osteogenesis. • Eliminate the morbidity associated with these procedures. • Allow implant rehabilitation in situations that normally would not allow to obtain good prosthetic outcomes, for example, after maxillary tumor ablation surgery.

Table 9.8 Meta-analysis comparison of tilted versus axially placed implants – survival

Menini and coll. [18] Maxilla only Risk ratio (95 % CI) Chracanovic and coll. Risk ratio (95 % CI)

Studies included Retrospective and prospective studies

Retrospective and prospective studies

Tilted versus axially placed Effect size implants RR (95 % CI) 1.23 (0.66–2.30)

RR (95 % CI) 1.89 (1.35–2.66)

Favoring Axially placed

Statistically significant No (p-value 0.575)

Axially placed

No (p-value 0.450)

Table 9.9 Meta-analysis tilted versus axial – MBL change

Menini and coll. [18] Maxilla only Monje and coll. [68] Del Fabbro and coll. [16] Chrcanovic and coll. Subgroup mandible Subgroup maxilla

Studies included Retrospective and prospective studies

Effect size Mean difference in mm (95 % CI)

Tilted versus axially placed implants 0.02 (−0.05–0.09)

Retrospective and prospective studies Retrospective and prospective studies Retrospective and prospective studies

Mean difference in mm (95 % CI) Mean difference in mm (95 % CI) Mean difference in mm (95 % CI)

−0.13 Axially placed No (−0.041–0.298) (p-value 0.137) −0.06 Axially placed No (−0.12–0.01) (p-value 0.05) 0.77 (0.39–1.52) Axially placed No (p-value 0.450)

Statistically Favoring significant Axially placed No (p-value 0.575)

1.70 (1.05–2.74) Axially placed Yes p-value (0.03)

Implant Prosthodontics

Disadvantages are: • Invasive surgery • Risk of damaging delicate structures like the orbital cavity • Need of sedation or general anesthesia compared to other implant surgery techniques Zygoma implants are available in lengths up to 50 mm; the most common diameter is 3.75 mm. Traditional protocols include the placement of two zygoma implants associated with two to four traditional implants in the anterior maxilla. This is a protocol that can be followed when the anterior maxilla is not excessively atrophied; otherwise, placement of two zygoma implants per side will serve as the retention for the prosthesis. Chrcanovic and coll. reported five different surgical techniques available for zygoma implant insertion [19]. The classical approach (Fig. 9.8) begins with the exposure of the maxillary bone up to the infrazygomatic crest, finally reaching the zygomatic bone for a complete visualization. After identification of the infraorbital nerve, a window at the sinus wall is made. The sinus mucosa is reflected, and the entrance from the maxillary crest with a round bur is made through the sinus. When the zygoma bone is reached and the implant site prepared, the implant is inserted manually to the proper depth.

Fig. 9.8 Classical approach for zygoma implant placement (Reproduced with permission from Chrcanovic and coll.)

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The sinus slot technique (Fig. 9.9) is similar to the traditional approach, but instead of raising the whole sinus mucosa, a space or “slot” is created along the insertion path of the implant into the maxillary bone up to the base of the zygoma, such that the whole implant threads are exposed for visualization. The smaller antrostomy that results renders this technique less invasive. The exteriorized approach (Fig. 9.10) does not include antrostomy; therefore, the implants are placed outside the sinus. Osteotomy is performed in the zygoma bone and widened progressively. Custom-made drill guide (Fig. 9.11) is a minimally invasive technique that involves the use of a 3D model manufactured on the basis of a CBCT scan, and finally the drill guide is produced with stereolithography. This should allow positioning of the implant without antrostomy. Computer-aided surgery involves the use of intraoperatory navigation system that can allow, in theory, to execute a flapless procedure. The authors concluded that the choice of a technique over another is a matter of personal preferences due to the lack of comparative studies. On the other hand, there are situations that lead to prefer a given surgical approach. In detail, a severe resorption with a prominent concavity between the zygoma and the maxilla suggests the

Fig. 9.9 Sinus slot technique for zygoma implant placement (Reproduced with permission from Chrcanovic and coll.)

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Fig. 9.10 Exteriorized approach for zygoma implant placement (Reproduced with permission from Chrcanovic and coll.)

specialized centers are involved in the placement of this kind of implants [21–23]. Wang and coll. [22] included three studies in their systematic review with a total of 196 implants placed in 49 patients; the reported weighted mean survival rate was 96.7 % (92.5– 98.5 CI 95 %). Despite this, the study suggests the reliability of zygoma implants in full-mouth maxillary rehabilitation (Fig. 9.12); no RCTs are available, and further studies are needed to give strength to these results. Zygomatic implants are very useful solutions in those cases in which other options are unfeasible, especially post-oncologic ablation patients and very severe atrophy of the upper jaw. The delicate structures involved in the placement procedures should be taken into account; therefore, placement of zygomatic implants should be limited to experienced surgeons, in adequate structures ready to face the possible complications which may occur.

9.1.5

Fig. 9.11 Custom-made drilling for zygoma placement (Reproduced with permission from Chrcanovic and coll.)

use of an exteriorized approach; the contrary happens when no concavity is present, and the classical or slot techniques should be employed. Regarding the custom-made drill guides and computer-aided surgery, their use still needs to be validated. Moreover, they’re more expensive and limited to centers where the necessary equipment is available. The most common complications as reported in the literature are sinusitis in up to 21 % of patients, implant failure in up to 11 % of patients, and perforation of the orbit in to 6 % of patients. Maxillary or zygomatic nerve deficits and intracranial penetration are also reported in the literature, but these serious complications are limited to single case reports [20]. Reported survival rates of zygoma implants are in the range of 95.6–100 %. The high survival rates are likely dependent by the fact that careful patient selection and skilled clinicians in

The All-on-Four Concept

The All-on-FourTM is a prosthetic design concept (Nobel Biocare, Goteborg, Sweden) which employs four implants in the anterior jaw (maxilla or mandible), of which the central two are vertically placed, while the most distal are maximally angulated in order to minimize the cantilever length and support a full-arch, provisional, immediately placed fixed prosthesis (Fig. 9.13). No RCTs are available for evaluation of this prosthetic solution compared to other ones, but a systematic review [24] analyzed six prospective and retrospective studies for evaluation of effectiveness and long-term success of the All-on-Four protocol. The follow-up in the included studies ranged from 12 to 36 months. Studies reported success rates for the implants in the range of 98.6–99.1 % and for the prostheses from 99.9 to 100 %. Anyway, this high survival rates need to be taken cautiously. First, the majority of the studies included were conducted in Italy and Portugal by experienced clinicians that had a huge experience with this procedure, so it is difficult to understand if these excellent results may be replicated by the average practitioner in the everyday practice. Second, the lack of RCTs and

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b e

Fig. 9.12 (aâ&#x20AC;&#x201C;e) Zygomatic implant placement (a). Maxillary prosthesis (b, c). Delivery of the prosthesis and X-ray showing the correct placement of the implants up to the zygomatic bone (d, e)

the short follow-up periods does not allow to draw any certain conclusion. Undoubtedly, longterm studies with follow-ups of at least 5 years are necessary.

9.2

Optimal Number of Implants for Fixed Reconstructions

One of the questions that accompanied the dental implant practice since its beginning is about the optimal number of implants that guarantees the best clinical results.

Addressing this question, it is not an easy task; in the past, some clinicians advocated the option of one implant for every missing tooth, but clinical results have shown that this is not the case. Nevertheless, there is still a lack of clarity when the issue of the ideal number of implant is analyzed. Mericske-Stern and coll. [25] tried to find answers to the question reviewing the evidence of the past 30 years. The authors concluded that despite the lack of long-term studies and RCTs regarding the implant number and prosthetic

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recalled that four implants of standard dimensions (≥10 mm long and ≥3.5 mm in diameter) can be considered a valid alternative in the maxilla. Also Heidecke and colleague [27] assessed the 5-year survival ad complication rates of implant-supported fixed reconstructions in partially and totally edentulous patients in the attempt to establish the optimal number of implants according to a specific type of reconstruction (FDP or full arch). The results of the analysis were considered just extrapolation from studies performed for other kind of evaluation, given that no trial exists that specifically attempts to answer the original question. Therefore, the authors concluded that four to six implants in the edentulous jaws are a good number for full-arch restorations, while for FDP the evidence remains unclear.

9.3

Fig. 9.13 (a–c) Example of a mandibular All-on-Four implant placement and restoration

design, consistent results are reported in the implant literature. In particular, high survival rates and relatively low risks of complications are achieved regardless of the number of implants used. The majority of articles to rehabilitate edentulous jaws report four to six implants; therefore, this seems a reasonable number for full-mouth rehabilitation with implants ≥10 mm long. At the FOR Consensus Conference in 2014 [26], it was established that a sufficient number of implants for full-mouth restorations with fixed prostheses consisted of four implants in the mandible and six in the maxilla. Moreover, it was

Implant Overdentures

It is common for edentulous patients wearing a maxillary or mandibular complete removable denture to suffer from insufficient stability or poor retention of the prostheses. This may have a huge detrimental impact on chewing abilities, phonation, esthetics, and quality of life as a whole. Implant overdentures (OVD) aim at overcoming these problems conferring better retention, function, and phonetics. OVD are defined as complete dentures partially supported by dental implants. Some authors have proposed the distinction between implantsupported and implant-retained OVD, the first referring to a prosthesis entirely supported by implants and the second instead retained by dental implants but finding its support on the mucosa as well [28]. Analysis of the literature allows to evaluate the various attachment systems and optimal number of implants which should ensure optimal survival and complication rates of the implants and the OVD prosthetic components. Different attachment systems for mandibular and maxillary OVD exist.

Implant Prosthodontics

Bar, ball, magnets, and telescopic attachments are the most commonly employed mechanisms of retention [29]. • A bar (Fig. 9.14) mechanism has the purpose of splinting the abutment teeth and at the same time support the prostheses. • Ball (Fig. 9.15) attachments are the simplest type, constituted by a small ball on the implant which houses a corresponding space contained within the prostheses. • Telescopic attachments (Fig. 9.16) are made of a primary coping attached to the implant which inserts in a secondary coping present within the prostheses. • Magnets (Fig. 9.17) are composed of the rare Earth material neodymium-iron-boron (NdFe-B) which is the most powerful magnet available or another rare material which is samarium-cobalt (Sm-Co). In general, the selection of an attachment system has been dependent on the preferences of

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the clinician, but it should be important to understand if treatment outcome is in some way dependent by the type of attachment chosen. Kim and coll. [30] systematically reviewed the publications on this topic; in their research, they included RCTs and prospective studies with follow-up in the range of 1–10 years. Survival rate of implants ranged from 97 % to 100 % with a mean survival of 98 %. Magnet attachments were most

Fig. 9.15 Example of ball attachments

b b

Fig. 9.14 (a, b) Example of bar attachment for a mandibular OVD

Fig. 9.16 (a, b) Example of telescopic attachments

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Fig. 9.17 (a, b) Example of magnetic attachments (Reproduced with permission from Chu and coll.)

commonly affected by complications due to wear and corrosion. These complications were more frequent with old magnetic materials such as AlNiCo, but with new materials such as Nd-Fe-B or Sm-Co, they can be potentially reduced. Clip loosening in bar attachments and matrix loosening in ball attachments were the second most common reported complications. Andreiotelli and coll. [28] evaluated RCTs and prospective studies with follow-up ≥5 years. The authors found that information regarding mandibular OVD was found more commonly than maxillary one. Results showed that implant survival was in the range of 93–100 % at 10 years and did not seem to depend by splinting or the number of implants employed. Implant survival was higher for the mandibular OVD compared the maxillary ones. Prosthetic success ranged greatly and was not calculated cumulatively; therefore, a numerical synthesis between the various studies was not performed. In order of frequency, the most common reported complications were loss of retention,

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need of rebasing/relining, attachment fracture, OVD fracture, opposing prosthesis fracture, acrylic resin fracture, abutment screw loosening, and implant fracture. Higher incidence of complications was observed for the maxillary OVD in respect to the mandible. Although it was considered not feasible to perform an objective assessment of the retention systems, it was any way possible to observe that the majority of the studies outlined a substantial lack of difference in terms of implant survival between splinted and unsplinted OVD. Single attachments are less costly and easier to manufacture; therefore, it should be preferable to adopt them instead of a bar retaining system. The ball retentions seem to show the highest retentive capacity. On the opposite side, magnets and bars tend to show a decrease of the retention capacity over time. Also, it was observed that there seems to be no correlation between attachments and prosthetis, aside from bars with distal cantilever that show a higher degree of fractures. Regarding the optimal number of implants for mandibular implant OVD, a systematic review of RCTs and prospective studies with a follow-up ranging from 1 to 10 years [31] draw the conclusion that the prognosis of OVD is excellent and implant survival rates were similar between the one, two, and four implant OVD designs; it was concluded that high survival rates can be obtained regardless of the number of implants inserted. Also, denture maintenance and patient satisfaction scores seemed to be not affected by this factor. Raghoebar and coll. [32] specifically evaluated the ideal number of implants for the maxillary OVD. Considering that implant survival rates are generally lower than the mandibular ones, it is reasonable to assume that in order to prevent loss of the prostheses, a greater number of implants are required for maxillary OVD (Fig. 9.18). In fact, the meta-analysis showed an event rate/year for implant loss of 0.019 in case of ≥6 splinted implants compared to 0.030 event rate/ year for ≤4 splinted implants and 0.111 event rate/year for ≤4 unsplinted implants.

Implant Prosthodontics

Fig. 9.18 (a, b) Example of maxillary overdenture. In these cases, implants connected with a bar seem to be more reliable than other prosthetic solutions (Reproduced with permission from Slot and coll.)

About prostheses loss, the event rate/year was of 0.005 in case of ≥6 splinted implants, 0.031 for ≤4 splinted implants, and 0.012 for ≤4 unsplinted implants. This figures led to the conclusion that implant-supported maxillary OVD should be ideally supported by six implants splinted between each other, the minimum number being four splinted implants. The worst outcomes were observed with ≤4 unsplinted implants (Tables 9.10 and 9.11). Another similar systematic review, on studies with a mean observation period of 1 year [33], arrived at similar conclusions. The survival rate of both prostheses and implants was >95 % for all the design configurations analyzed (six splinted implants, four splinted implants, four implants with bar attachments). Anyway, the best results were obtained with six splinted implants, followed by four splinted implants, the least successful being the four implant ball design. For this reason, it was

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concluded that four implants maxillary OVD need to be considered as a second-line treatment option, although good results can be obtained in any case. The McGill consensus statement, published after the symposium held at McGill University in Montreal, recommended that the minimal acceptable treatment for the fully edentulous mandible is the two implant OVDs. This was not intended as the best treatment option but instead the minimally acceptable solution for patients that cannot undergo more extensive prosthetic and implant treatment [34]. This concept was widely validated by numerous RCTs. In a recent meta-analysis [35], the patient-assessed quality of life evaluated with a Visual Analogue Scale was considered to be higher in patients having an implant-supported OVD compared to conventional denture wearers. Also the functional aspects, such as chewing ability and phonation, were notably improved with the adoption of an implant-supported OVD. In light of this, it is possible to state that the McGill consensus statement in which two implant OVDs are the minimally acceptable treatment options for the fully edentulous patient should be fully incorporated in clinical practice at any level. An aspect that merits consideration is the degree of MBL around implants retaining or supporting OVDs. When literature is systematically reviewed, attachment type and implant design do not seem to influence the MBL change [36] although the high heterogeneity of the studies reporting this value does not allow to draw strong conclusions at this regard. Finally, maintenance of OVD is an aspect investigated by researchers in light of the fact that it reflects the chair time spent for this kind of treatment and has important economical repercussions. There is a general consensus in the literature that the highest frequency of reinterventions and readjustments is performed in the first year after loading. Loss of retention due to damage or wearing of the attachment system is the most common cause of reintervention. Also relining of the denture is a quite common

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160 Table 9.10 Maxillary OVD treatment – overdenture survival

Slot and coll. [33] Survival rate per year (95 % CI) Raghoebar and coll. [32] Survival rate per year (95 % CI)

Six implants and bar superstructure 98.1 % (96.4–99.0)

Four implants and bar superstructure 97.0 % (91.4–99.0)

Four implants not splinted 89.0 % (96–97.4)

99.5 % (97.8–99.8)

96.9 % (92.4–98.7)

98.8 % (91.4–99.8)

Table 9.11 Overdenture complication reported rates OVD complications Andreiotelli and coll. [28]

Loss of retention 30 % Needs of rebasing/relining 19 % Clip or attachment fracture 17 % OVD fracture 12 % Opposing prosthesis fracture 12 % Acrylic resin fracture 7 % Prosthesis screw loosening 7 % Abutment screw loosening 4 % Abutment screw fracture 2 % Implant fracture 1 %

necessity, in the range of 6–18 % according to various authors (Table 9.7). In conclusion, implant-supported or retained OVD constitutes an excellent treatment option in edentulous denture wearers that for economical, surgical, or anatomical reasons cannot undergo extensive implant surgery for full-arch fixed dental prosthesis. From a review of the literature, it emerges that the various attachment systems available are all reliable although a possible increase in complications can occur with magnets and ball attachments. The presence of a bar does not seem to confer appreciable improvements in clinical outcomes for the mandibular OVD, whereas in the maxilla, six implants connected by a bar constitute a safer option in terms of implant and prosthesis survival. Finally, it was observed that mandibular OVD sustained by two implants gives excellent results and should be considered the treatment of choice for denture wearers. The choice of the attachment system does not influence the success and survival rates of implant and prostheses. Anyway, it seems that magnets are associated with an

increase in complications such as loss of retention, especially at long term.

9.4

Dental Implant Impressions

An accurate impression is one of the fundamental steps in the success of the implant treatment. Accuracy of the impression has a direct role in the accuracy of the cast and the proper fit of the definitive prosthesis. Various materials and techniques have been employed in implant dentistry, and choosing between them can be a challenge for the practitioner [37]. First of all, the ideal impression material should possess some basic properties: • Accuracy refers to the property of the material to reproduce the fine details in a precise way. An accurate material should be able to reproduce details with a limit of at least 25 μm. • Elastic recovery means that, after induration, the material is deformed by the undercut areas in the mouth during removal, but then it recovers its original shape. • Hydrophilia is another important property because it allows the material to flow even in the presence of saliva or blood. In fact, the more a material is hydrophilic, the more it can “spread” over a given surface. • Viscosity refers to the ease of the material to flow readily. It is important for a given material to possess an equilibrium in viscosity such that it can be contained in the tray without flowing away but at the same time maintain a certain degree of flowability into the small anatomic details.

Implant Prosthodontics

• Workability is the property of the material to be handled with ease for insertion in the mouth and at the same time possessing a setting time that allows impression taking without much discomfort for the patient.

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Two materials, belonging to the elastomeric class, have emerged as possessing all the qualities to achieve excellent results in implant dentistry. These are the polyethers and the addition silicones (polyvinylsiloxanes or PVS). Polyethers are available in low-, medium-, and heavy-body consistency. PVS are available as extra low, low, low medium, heavy, and very heavy (putty). Polyethers have shorter working times and are more hydrophilic compared to PVS, even if surfactants have been added to silicones in order to improve the wettability of these materials. On the other hand, PVS have the best elastic recovery. Both materials undergo shrinkage after polymerization in the order of −0.15–0.20 % after 24 h; this means that the models should be prepared as soon as possible if the maximum accuracy is desired. Three methods are commonly employed in making implant impressions, • Dual-viscosity technique, a low-consistency material is injected, usually through a syringe, on a higher viscosity material already present in the tray. • Monophase technique, impression is taken with a single, medium-viscosity material. • Putty-wash (Fig. 9.19) technique, a putty material is inserted in the tray, and a preliminary impression is taken. Then, in the created cavities, a low-consistency material is injected, and the preliminary reimpression is inserted. Regarding the techniques of impression coping, it is possible to differentiate between transfer (closed tray) and pickup (open-tray) techniques. In the transfer technique (Fig. 9.20), the impression copings remain in the mouth on

Fig. 9.19 (a, b) Putty-wash technique in which a putty material (the picture is purple in color) is inserted in the tray, and a first impression is taken. Then in the indentations left by the first impression, a low-consistency material (yellow in the picture) is injected, (a) and the final impression is taken (b)

Fig. 9.20 Transfer (closed tray) technique performed with a monophase material (polyether)

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removal of the set impression; their insertion occurs outside of the mouth on the indentations left on the impression. In the pickup technique (Figs. 9.21, 9.22, and 9.23), the impression copings and the analogues are screwed to the implant; an open tray is used to take the impression. With the tray still in the mouth, the analogues are removed, and finally the coping-impression assembly is removed together; at the end, the analogues will be connected to the copings outside of the mouth and sent to the laboratory. To ensure the maximal stability of all the components, there is the possibility to splint the copings together in the mouth with a scaffold formed of dental floss or orthodontic wire covered by a resin. Finally, digital impressions have emerged as possible alternatives to the traditional techniques (Figs. 9.24 and 9.25).

9.4.1

Regarding the assessment of implant impression technique accuracy, the majority of the available studies comprise in vitro evaluations. Linear distortion is the most common method used for the evaluation of impression accuracy, which is the assessment of the displacement on the x,y,z plane of the implant or abutment heads between each other after having established two reference points (such as the abutments themselves). Displacement is the most important factor determining the impression accuracy. Angular distortion instead aims at evaluating the rotation of the implant head around the implant long axis and the translation of the head along a reference plane. Due to the nature of the evaluations, only narrative reviews are available for assessment and comparison of various implant impression

Fig. 9.21 (aâ&#x20AC;&#x201C;d) Pickup (open-tray) technique, the coping is screwed to the implant (a). An open tray is used to take the impression (b). With the tray still in the mouth, the analogues are removed (c), and the coping-impression

Implant Impression Accuracy

assembly is finally removed from the mouth (d). Two materials (dual-viscosity method) of different consistency were used (PVS)

Implant Prosthodontics

Fig. 9.22 (aâ&#x20AC;&#x201C;c) A custom tray can be used for the pickup technique; this ensures greater comfort for the clinician and greater ease in impression taking. In this case, a monophase material was used (polyether)

techniques [38â&#x20AC;&#x201C;44]. Anyway, general conclusions can be drawn by analysis of the literature. In a recent review [38], including only in vitro studies, accuracy comparison of implant impression techniques was performed. Regarding the transfer versus pickup technique, it was found that a large part of the studies showed more accurate impressions with the open techniques, especially in case of four or more implants. The material evaluation evidenced that the most used and accurate material was the polyether, followed by PVS.

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Splinting techniques were also analyzed. Acrylic resin with dental floss splinting was the most often used. Also, sectioning of the resin before complete polymerization seemed to prevent the detrimental shrinkage effect to occur. Regardless of this, splinting impression technique was the most accurate compared to non-splinting. As expected, angulation of the implants presented the worst accuracy even if number of implants, adjacent teeth proximity, and implant height may also have an influence on accuracy. Finally, regarding digital impression, unclear evidence emerged mainly due to the lack of studies. It was concluded that high-accuracy scanners and the usage of powder particles as a marker give the best results. It is obvious that a current trend exists of shifting toward digitalization of implant procedures, and digital impression improvements may potentially lead to elimination of multiple materials and clinical/laboratory steps, but more studies are needed to confirm their clinical validity in comparison to the traditional procedures. In conclusion, it is possible to state that splinting seems to ensure a greater accuracy than nonsplinting technique. Sectioning of the resin before full polymerization has been advocated to give the best results. There is small difference between pickup/ open-tray and transfer technique, even if it seems that pickup technique may guarantee a better accuracy in case of divergent and multiple implants. Polyether and PVS show similar performances, but the first has been reported to be the most accurate. Finally, insufficient data exists on digital impression techniques to draw definitive conclusions.

9.5

Esthetics in Prosthetic Implant Dentistry

Optimal esthetic results depend by numerous factors. Of course, the prosthesis itself plays a fundamental role on the esthetic outcomes. The perfect mimicry with the natural tissues depends

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c f

Fig. 9.23 (aâ&#x20AC;&#x201C;f) Splinting of the implants with resin at the moment of taking, the impression ensures the greatest precision due to the absence of micromovement at the moment of tray removal from the mouth. In this case, the

scaffold for the resin was made with tooth floss (a, b); dual-viscosity materials (PVS) were used in an open-tray technique (c). Excellent reproduction of details for an immediate loading restoration (dâ&#x20AC;&#x201C;f)

upon the materials adopted and upon the perfect integrations of the implant and the prosthesis with the surrounding structures. Other factors such as implant position, provisional restorations, and timing of loading may have a role in obtaining optimal esthetic results. The review of Martin and coll. [45] addressed this topic, examining RCTs and prospective and case series studies published in the last decade.

Implants malpositioning seems to play a role in esthetic outcomes. In particular, an excessive buccal inclination of the implant increases the possibility to incur in mucosal recessions. Adoption of a provisional to allow proper adaptation and evaluation of the tissues before temporary restorations was strongly recommended because it allows the possibility of planning the final restoration. Moreover, soft tissue

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papilla index and other standardized objective evaluation systems. A true evidence-based comparison of esthetic outcomes in implant dentistry is impossible and this problem must be addressed in future studies.

9.5.1

Fig. 9.24 (a, b) Virtual impression techniques allow a digital view and study of the case

maturation was considered an essential prerequisite for excellent results. Regarding the retention system in relation to the esthetic outcomes, few studies available do not allow to propend to screw or cement retained. The problem that emerged from this analysis is a general lack of RCTs having esthetics as the first aim of evaluation. PES/WES scores are not uniformly reported; the same is true for the

Zirconia Versus Metal Ceramic

As already pointed out in the previous chapters, the use of zirconia has gained popularity due to its better esthetic mimicry with the natural dental tissues. The use of zirconia implant restorations is therefore aimed at improving the esthetic outcomes of the implant treatment in the cases in which the patient expects the best esthetic results. The worries expressed for other applications of ceramics (see Chaps. 4 and 5) in implant dentistry persist even for the prostheses manufacturing. In particular, the theoretical reduced mechanical performances in posterior regions of the mouth. When the literature is critically reviewed [46], it is found that implant-supported single crowns tend to show similar cumulative survival rates at 5 year (97.1 %) compared to the metal-ceramic restorations. The studies used for comparison present the usual problem of limited number of patients and follow-up, but results are anyway encouraging. Also, rates of complications associated with all-ceramic crowns were not different from the metal ceramic. Although it must be pointed out that these results can be different for FDP and full-arch restorations, because of their greater complexity. Veneer chipping was considered to be the most common technical complication of allceramic single crowns. In the same fashion, systematic reviews on zirconia FDPs [47, 48] showed excellent results at short-term clinical evaluation both in terms of survival than technical complications. The encouraging results must be balanced by the recognition of the fact that well-designed RCTs are missing in the dental literature. Also, some of the available studies lack in reporting some

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Fig. 9.25 (a–c) Example of digital impression taken with intraoral scan bodies and custom abutment fabrication (Reproduced with permission from Brandt and coll.)

important information such as the region of the mouth in which the restoration is placed, the type of restorations or the condition of the opposing dentition. At the current state, it is not possible to draw strong conclusions on zirconia restorations.

Bibliography 1. I. Sailer, S. Mühlemann, M. Zwahlen, C.H.F. Hämmerle, D. Schneider, Cemented and screw-retained implant reconstructions: a systematic review of the survival and complication rates. Clin. Oral Implants Res. 23, 163–201 (2012) 2. J.-G. Wittneben, C. Millen, U. Brägger, Clinical performance of screw- versus cement-retained fixed implant-supported reconstructions-a systematic review. Int. J. Oral Maxillofac. Implants 29(Suppl), 84–98 (2014) 3. M.S. Chaar, W. Att, J.R. Strub, Prosthetic outcome of cement-retained implant-supported fixed dental restorations: a systematic review. J. Oral Rehabil. 38, 697– 711 (2011) 4. M.L. De Brandão, M.V. Vettore, G.M. Vidigal Júnior, Peri-implant bone loss in cement- and screw-retained prostheses: systematic review and meta-analysis. J. Clin. Periodontol. 40, 287–295 (2013)

5. G.E. Romanos, B. Gupta, S.E. Eckert, Distal cantilevers and implant dentistry. Int. J. Oral Maxillofac. Implants 27, 1131–1136 (2012) 6. O.V. Padhye et al., Stress distribution in bone and implants in mandibular 6-implant-supported cantilevered fixed prosthesis: a 3D finite element study. Implant Dent. 24(6), 680–685 (2015) 7. J. Park, H. Kim, E. Park, M. Kim, S. Kim, Three dimensional finite element analysis of the stress distribution around the mandibular posterior implant during non-working movement according to the amount of cantilever. J Adv Prosthodont. 6(5), 361–371 (2014) 8. C. Wang, Q. Li, C. McClean, Y. Fan, Numerical simulation of dental bone remodeling induced by implantsupported fixed partial denture with or without cantilever extension. Int. J. Numer. Meth. Biomed. Eng. 29, 1134–1147 (2013) 9. L. Torrecillas-martínez et al., Effect of cantilevers for implant-supported prostheses on marginal bone loss and prosthetic complications: systematic review and meta-analysis. Int. J. Oral Maxillofac. Implants 29(6), 1315–1321 (2014) 10. E. Romeo, S. Storelli, Systematic review of the survival rate and the biological, technical, and aesthetic complications of fixed dental prostheses with cantilevers on implants reported in longitudinal studies with a mean of 5 years follow-up. Clin. Oral Implants Res. 23, 39–49 (2012)

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167 28. M. Andreiotelli, W. Att, J.-R. Strub, Prosthodontic complications with implant overdentures: a systematic literature review. Int. J. Prosthodont. 23, 195–203 (2010) 29. N.H.M. Alsabeeha, A.G.T. Payne, M.V. Swain, Attachment systems for mandibular two-implant overdentures: a review of in vitro investigations on retention and wear features. Int. J. Prosthodont. 22, 429–440 (2009) 30. H.-Y. Kim, J.-Y. Lee, S.-W. Shin, S.R. Bryant, Attachment systems for mandibular implant overdentures: a systematic review. J. Adv. Prosthodont. 4, 197–203 (2012) 31. J.-Y. Lee, H.-Y. Kim, S.-W. Shin, S.R. Bryant, Number of implants for mandibular implant overdentures: a systematic review. J. Adv. Prosthodont. 4, 204 (2012) 32. G.M. Raghoebar, H.J.A. Meijer, W. Slot, J.J.R. Slater, A. Vissink, A systematic review of implant-supported overdentures in the edentulous maxilla, compared to the mandible: how many implants? Eur. J. Oral Implantol. 7(Suppl 2), S191–S201 (2014) 33. W. Slot, G.M. Raghoebar, A. Vissink, J.J. Huddleston Slater, H.J.A. Meijer, A systematic review of implantsupported maxillary overdentures after a mean observation period of at least 1 year: review article. J. Clin. Periodontol. 37, 98–110 (2010) 34. J.M. Thomason, S.A.M. Kelly, A. Bendkowski, J.S. Ellis, Two implant retained overdentures - A review of the literature supporting the McGill and York consensus statements. J. Dent. 40, 22–34 (2012) 35. E. Emami, G. Heydecke, P.H. Rompre, P. de Grandemont, J.S. Feine, Impact of implant support for mandibular dentures on satisfaction, oral and general health-related quality of life: a meta-analysis of randomized controlled trials. Clin. Oral Implants Res. 20, 533–544 (2009) 36. M.C. Cehreli, D. Karasoy, A.M. Kökat, K. Akça, S. Eckert, A systematic review of marginal bone loss around implants retaining or supporting overdentures. Int. J. Oral Maxillofac. Implants 25, 266–277 (2010) 37. W. Chee, S. Jivraj, Impression techniques for implant dentistry. Br. Dent. J. 201, 429–432 (2006) 38. H. Lee, J.S. So, J.L. Hochstedler, C. Ercoli, The accuracy of implant impressions: a systematic review. J. Prosthet. Dent. 100, 285–291 (2008) 39. J.-H. Kim, K.R. Kim, S. Kim, Critical appraisal of implant impression accuracies: a systematic review. J. Prosthet. Dent. 114, 1–9 (2015) 40. M.R. Baig, Accuracy of impressions of multiple implants in the edentulous arch: a systematic review. Int. J. Oral Maxillofac. Implants 29, 869–880 (2014) 41. N. Chaimattayompol, D. Park, A modified putty-wash vinyl polysiloxane impression technique for fixed prosthodontics. J. Prosthet. Dent. 98, 483–485 (2007) 42. T.E. Donovan, W.W.L. Chee, A review of contemporary impression materials and techniques. Dent. Clin. North Am. 48, 445–470 (2004) 43. A.H.J. Moreira, N.F. Rodrigues, A.C.M. Pinho, J.C. Fonseca, J.L. Vilaça, Accuracy comparison of

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E v i d e n c e - B a s e d Pro s t h o d o n t i c s Fundamental Considerations, Limitations, and Guidelines Avinash S. Bidra,

BDS, MS

KEYWORDS Evidence-based dentistry Prosthodontics Guidelines Systematic reviews Randomized controlled clinical trials Prospective studies Retrospective studies KEY POINTS Prosthodontics is a unique specialty that offers numerous advantages and disadvantages for application of principles of evidence-based dentistry (EBD). An important difference between medical and dental models of care is the level of control a patient has about how, when, and whether it is necessary to treat a dental problem. This is especially true in the discipline of prosthodontics. Hence, an absolute extrapolation of evidence-based concepts from medicine to prosthodontics is not possible. Current lack of â&#x20AC;&#x153;strongâ&#x20AC;? evidence for a particular treatment does not necessarily imply that the treatment is â&#x20AC;&#x153;inferiorâ&#x20AC;? or â&#x20AC;&#x153;clinically ineffective.â&#x20AC;? Efforts should be targeted, however, to improve the future scientific evidence for such treatments. Due to the unique nature of prosthodontics, it is necessary to establish a consensus on guidelines for reporting prosthodontic outcomes. These guidelines can ensure that investigators provide standardized reporting of their studies in order for them to be clear, complete, and transparent and allow integration of their evidence into clinical practice. In order to teach and understand evidence-based prosthodontics, academicians and clinicians need to attain new skills pertaining to computer-based knowledge systems. These skills are necessary to use scientific evidence for the 5-step process of asking, acquiring, appraising, applying, and assessing. Evidence-based prosthodontics can change the future course of prosthodontics education, patient care, reimbursements, research agendas, and oral health policies that have an impact on prosthodontics.

INTRODUCTION

The traditional model of care in dentistry involves use of individual clinical expertise and patient treatment needs to provide dental care (Fig. 1). This model of care has been used for centuries across the world and is primarily based on observations, beliefs, and personal and expert opinions. Although this model has not led to any Department of Reconstructive Sciences, University of Connecticut Health Center, 263 Farmington Avenue, L6078, Farmington, CT 06030, USA E-mail address: avinashbidra@yahoo.com Dent Clin N Am 58 (2014) 1â&#x20AC;&#x201C;17 http://dx.doi.org/10.1016/j.cden.2013.09.001 dental.theclinics.com 0011-8532/14/$ â&#x20AC;&#x201C; see front matter Ă&#x201C; 2014 Elsevier Inc. All rights reserved.

Bidra

Fig. 1. Traditional model of care in dentistry involves use of individual clinical expertise and patient treatment needs to provide dental care.

devastating effects in dentistry, it precludes systematic assimilation, acceptance, and assessment of new treatment effects. Furthermore, it provides minimal confidence to clinicians for making clinical decisions for new scenarios and new treatments. The term, evidence-based practice, is defined as “the conscientious, explicit and judicious use of current best evidence in making decisions about the care of the individual patient. It means integrating individual clinical expertise with the best available external clinical evidence from systematic research.”1 This definition stems from the medical perspective, and dentistry is more familiar with the term, EBD. Currently, there is no definition for evidence-based prosthodontics but it is understood that it encompasses the application of EBD with respect to prosthodontics. According to the American Dental Association (ADA), EBD is defined as “an approach to oral healthcare that requires the judicious integration of systematic assessments of clinically relevant scientific evidence, relating to the patient’s oral and medical condition and history, with the dentist’s clinical expertise and the patient’s treatment needs and preferences.”2 Therefore, the EBD process is not a rigid methodologic evaluation of scientific evidence that dictates what practitioners should or should not do but also relies on the role of individual professional judgment and patient preference in this process (Fig. 2).3 NEED FOR EVIDENCE-BASED PROSTHODONTICS

With rapid advancements in dental materials and dental technology and improved understanding of clinical outcomes, a surfeit of research has been published in prosthodontics and dental implant–focused literature (Box 1). Furthermore, a surplus amount of published research exists in interdisciplinary fields that are of critical importance to prosthodontics. It is well known that not all published literature is scientifically valid and clinically useful. Therefore, a critical analysis of the quality of published research and consolidation of the excess scientific information is necessary to render them significant and useful. In an extensive analysis of scientific publications between 1966 and 2005, Harwood4 noted that there were 44,338 published articles in prosthodontics. Of these, there were 955 randomized controlled clinical trials (RCTs) (2%). Nishimura and colleagues5 identified 10,258 articles on prosthodontic topics between 1990 and 1999 and estimated that to stay current in the year 2002 would require reading and absorbing approximately 8 articles per week, 52 weeks per year, and across 60 different journals. These numbers do not include published articles on implant dentistry. Russo and colleagues6 identified 4655 articles published between

Evidence-Based Prosthodontics

Fig. 2. EBD involves integration of best available scientific evidence along with individual clinical expertise and patient treatment needs to provide dental care.

1989 and 1999 dedicated to implant dentistry and estimated that to stay current in the year 2000 would require reading and absorbing approximately 1 to 2 articles per week, 52 weeks per year. It is not difficult to assume that these numbers are significantly higher in the year 2013 and will continue to grow due to increased growth in the number of journals and publications, underscoring the need for computer-based clinical knowledge systems and for clinicians to acquire new skills to use the best available scientific evidence (BASE) (Box 2). EPIDEMIOLOGIC BACKGROUND

The epidemiologic background for evidence-based practice dates back to the nineteenth century, to the work of John Snow, who is widely regarded as the father of modern epidemiology.7 Snow rejected the popular miasma theory as the cause of the cholera outbreaks in England. Through a systematic method of data collection and analysis, Snow established a classic case-control study and traced the cholera outbreaks to drinking water contamination from the sewage systems. His ideas were rejected, criticized, and not embraced until several years after his death. Similar to Snowâ&#x20AC;&#x2122;s experiences, other landmark events in modern epidemiology include

Box 1 The need for evidence-based prosthodontics Enable the recognition of best available scientific evidence in prosthodontics. Consolidate the scientific information overload in prosthodontics and related literature. Scrutinize the scientific basis for existing prosthodontic treatments. Improve current and future treatments. Encourage improvement in the quality of clinical research as well as in reporting. Distinguish and advance the specialty of prosthodontics.

Bidra

Box 2 New skills required by clinicians to adopt evidence-based prosthodontics Asking the appropriate research question for a clinical situation of interest. Acquiring information through efficient scientific literature search. Appraising the acquired information. Applying the acquired information to clinical practice, along with individual clinical expertise and patient preferences. Assessing the results of the applied intervention to optimize the clinical situation.

Semmelweisâ&#x20AC;&#x2122;8 important discoveries on hand washing intervention to drop maternal mortality rates and childbed fever and Doll and colleaguesâ&#x20AC;&#x2122;9 systematic observations on cigarette smoking and its association with lung cancer. Several other similar events have all had a significant impact on worldwide public health. Pioneering efforts in the twentieth century by Archibald Cochrane called for stateof-the-art systematic reviews (SRs) of all relevant RCTs in health care,10 leading to the creation of the world-renowned Cochrane Collaboration in 1993 to organize all medical research information in a systematic manner in the interests of evidencebased medicine. The term, evidence-based medicine, itself was first described in the medical literature in 1992 by a working group of a similar name, who stated that this would be a new way of teaching the practice of medicine.11 The ADA has espoused the principles of evidence-based practices since its inception and has made remarkable progress over the past 20 years to render popularity to the current known principles of EBD for use in clinical practice and dental education. CONSIDERATIONS IN PROSTHODONTICS

An important difference between medical and dental models of care is the level of control a patient has about how, when, and whether it is even necessary to treat a dental condition. This is especially true in the discipline of prosthodontics. Prosthodontics is a unique dental specialty that encompasses art, philosophy, and science and includes reversible and irreversible treatments. Therefore, an absolute extrapolation of evidence-based concepts from medicine to prosthodontics is not possible. Treatment outcomes, which are a core element of prosthodontics, however, render themselves well for application of principles of EBD. There are 3 predominant items that are important to understanding challenges in reporting treatment outcomes in prosthodontics. Defining the Outcomes of Clinical Interest

Key issues in defining clinical outcomes in prosthodontics are multifaceted due to the inherent nature of the treatment. Some examples of these issues include differentiating success versus survival, complications versus consequences, and prosthesis outcomes versus patient-centered outcomes. Another important characteristic is defining the appropriate endpoint of a clinical study. Hujoel and DeRouen12 have categorized clinical endpoints (outcomes) as surrogate endpoints and true endpoints. Surrogate outcomes include measures that are not of direct practical importance but are believed to reflect outcomes that are important as part of a disease/treatment process. True outcomes, however, reflect unequivocal evidence of tangible benefit to patients. Both types of outcomes are important in prosthodontics, because surrogate outcomes are helpful for preliminary evidence and true outcomes are helpful for definitive evidence (Table 1).

Evidence-Based Prosthodontics

Table 1 Understanding differences between surrogate and true outcomes in clinical trials in prosthodontics Surrogate Outcomes

True/Definitive Outcomes

Includes measures that are not of direct practical importance but are believed to reflect outcomes that are important as part of a disease/treatment process12

Reflects unequivocal evidence of tangible benefit to the patient

Examples Pocket depth Open margins Peri-implant bone level Prosthesis retention/support

Corresponding examples Tooth/implant survival Secondary caries Implant survival Patient satisfaction

Endpoints are â&#x20AC;&#x153;softerâ&#x20AC;? and easier to measure and studies are relatively inexpensive.

Endpoints are â&#x20AC;&#x153;harderâ&#x20AC;? and difficult to measure and studies can be more expensive.

Do not have a direct impact on changes in clinical practice or changes in public health policies.

Can have a direct impact on changes in clinical practice and/or changes in public health policies.

Duration Needed to Appropriately Study the Outcomes

The time period needed to study a clinical outcome of interest depends on the definition of a treatment outcome, surrogate or true endpoint desired, treatment effect desired, and adverse events related to a treatment under investigation. Currently, there is no consensus in prosthodontics on definitions for preliminary, short-term, or long-term studies. Therefore, it becomes the prerogative of the investigator, editor, and reader to decide if the result of a study reports on short-term or long-term outcomes. Often, a study with a follow-up period of up to 6 years is described as â&#x20AC;&#x153;long-term follow-upâ&#x20AC;? where only a meager number of samples have actually made it to a 6-year follow-up and the rest have a follow-up of less than 2 years. It is understood that preliminary and short-term studies have high clinical impact when they report failures of a particular treatment; only long-term studies can have high clinical impact for treatment success. Treatment success reported in short-term studies, however, can lay the justification whether additional research is needed. Minimum Sample Needed to Study the Outcome of Interest?

The sample size of a study depends on the difference in treatment effect desired. In prosthodontics, it is difficult to obtain large sample sizes from a single study center because of the elective and expensive nature of prosthodontic treatment, which has led to a large body of published research in the prosthodontic literature with small sample sizes. For a study to have a large clinical impact and provide sufficient evidence to change a particular clinical practice, sample size is critical. Currently, there is no consensus in prosthodontics on definitions for sample sizes as small, moderate, and large. The validity of defining such sample sizes is currently unknown. LEVELS OF EVIDENCE AND PROSTHODONTICS

Evidence in medicine has been popularly categorized into 5 hierarchical levels and widely represented as a pyramid with the â&#x20AC;&#x153;weakest/lowest level of evidenceâ&#x20AC;? at the base and the â&#x20AC;&#x153;strongest or highest level evidenceâ&#x20AC;? at the apex (Fig. 3). This gradation

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Fig. 3. Evidence in medicine has been popularly categorized into 5 hierarchical levels and widely represented as a pyramid with the “weakest/lowest level of evidence” at the base and the “strongest or highest level evidence” at the apex. This model may not be applicable to prosthodontics.

has been used by several health agencies across the world. Although the 5 hierarchical levels of evidence and the pyramidal representation may be popular in medicine, the applicability of this paradigm to prosthodontics is questionable because few articles in prosthodontics comprise RCTs and large cohort studies, implying that most current clinical practices in prosthodontics are all based on “weak evidence.” Additionally, 2 critical elements of importance to prosthodontics that are omitted from the evidence-based pyramid are sample size and duration of a study. As previously discussed, these 2 elements can significantly affect the way evidence has an impact on clinical practices. For example, results from a cohort or a case-control study with a very large sample size and/or a long-term follow-up on all-ceramic crowns can have a better impact on clinical decisions compared with results from an RCT with a small sample and a short-term follow-up. In this scenario, in spite of RCT regarded as the “strongest evidence,” it would fail to be used by clinicians for confident decision making. Furthermore, major medical breakthroughs have originated from cohort and case-control studies, which are considered by many as “weaker” forms of evidence. The terms, weak and strong, are subjective and exclusive and do not lend themselves to an unbiased assessment of best available evidence in prosthodontics. Therefore, an alternative approach for prosthodontics literature is suggested. The suggested paradigm involves a horizontal spectrum encompassing 3 stages of evidence— preliminary evidence, substantive evidence, and progressive evidence (Fig. 4). Preliminary Evidence Expert/experience-based opinions, philosophies, theories, and biologic plausibilites

Expert opinion is the oldest form of evidence in health care for centuries and continues to remain one of the most popular forms of evidence in contemporary dentistry because it is easy for clinicians to acquire and apply the presented evidence. Expert/ experience-based opinions and monographs have dominated the art component of

Evidence-Based Prosthodontics

Fig. 4. The suggested new paradigm involves a horizontal spectrum encompassing 3 stages of evidenceâ&#x20AC;&#x201D;preliminary evidence, substantive evidence, and progressive evidence.

prosthodontic literature for almost a century. Additionally, they have a strong representation in the discipline of dental occlusion, dental techniques, choice of dental materials, and dental technology. Expert opinions, philosophies, theories, and biologic plausibilities are all important, because they provide a starting point to initiate and propel new ideas, theories, and innovations and develop further research. Unfortunately, many expert opinions are biased and scientifically not validated. As a result, several popular opinions and philosophies in prosthodontics have not been clinically validated. Some examples include need for balanced occlusion in complete dentures, designs for removable partial dentures, tooth preparation designs, types of restorations in fixed prosthodontics, and many others. Laboratory studies and animal studies

A large body of research in dentistry falls into the category of laboratory studies and animal studies. Compared to clinical research, this type of research is easier to conduct, accomplished faster and allows different types of hypotheses to be tested in a controlled setting. In prosthodontics, due to rapid emergence and advancements of new dental materials, dental technology, and improved biologic understanding, these studies are important because they provide a good foundation before proceeding with clinical studies. Pioneering work on osseointegration done by PI Branemark in his animal/laboratory studies and its subsequent development through progressive research is a testimony for this type of preliminary research. In the discipline of dental materials, independent investigators with a clinical understanding should verify research done by the industry. Studies with promising results should then be progressed to subsequent stages of research. Unfortunately, this paradigm is not often followed in prosthodontics and many dental materials and technology have been used clinically based on laboratory studies alone. Case reports and case series

A single case report/case study describes the unique characteristics and treatment of a single patient, and a case series describes the treatment in a group of patients. With regards to sample size, currently there is no consensus on when a study can be defined as a case series versus a cohort study. It is understood, however, that case series are descriptive in nature and involve a small heterogeneous sample as opposed to a cohort study, which is observational and analytic in nature. Nevertheless, case reports and case series have high sensitivity for detecting novelty and form the basis for detecting new concepts, etiologic clues, side effects, and new treatments and have contributed to major breakthroughs in medicine.13 In prosthodontic literature, case reports/series typically depict management of unique situations through unique techniques and/or unique materials. Such reports not only help clinicians in management

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of similar situations but also aid in laying the foundation for future laboratory studies and clinical trials. Substantive Evidence Cross-sectional studies/surveys and descriptive studies

A cross-sectional study is defined as a study measuring the distribution of some characteristic(s) in a population at a particular point in time.14 Essentially, the exposure and outcome are measured simultaneously, at the time of the survey. This study design is helpful for preliminary analysis of the prevalence of a condition/disease at a given point of time and for investigating the potential risk factors or causes of the condition.15 An example in prosthodontics is a cross-sectional study to analyze the prevalence of halitosis in patients with fixed complete dentures. In this example, because there is no temporal assessment, it is difficult to conclude that halitosis is related to fixed complete dentures. However, if significant numbers of samples are from a certain social or ethnic background, have a history of smoking or poor oral hygiene, then the researcher can investigate further to delineate the risk factors. Descriptive studies are studies that describe a particular characteristic and any related changes due to an intervention. They are commonly reported in prosthodontics with respect to anatomic variations and esthetic-related characteristics. Therefore, temporal considerations, cause-effect analysis, and survival outcomes are usually not applicable to such studies, which does not mean that the evidence from these studies is “weak.” Major understanding of complete denture principles and esthetic dentistry has resulted from such studies. These studies are specific to a given population, however, and describe preliminary data or trends that may or may not be extrapolated to different populations. Some descriptive studies, however, have large sample sizes encompassing different countries and races.16 Case-control studies

A case-control study is defined as “a study that compares people with a specific disease or outcome of interest (cases) to people from the same population without that disease or outcome (controls), and which seeks to find associations between the outcome and prior exposure to particular risk factors.”14 Case-control studies are not commonly described in the core prosthodontics literature, probably because prosthodontics typically does not deal with diseases and cure but with treatment outcomes. Compared with cohort studies, they are inexpensive and afford potential for large sample sizes. As a rule, they cannot prove causation, so cohort studies and RCTs are subsequently needed to test a causal hypothesis. Therefore, they are often associated with controversies and have a potential for propaganda by the media. A popular recent example that is relevant to prosthodontics is a case-control study linking the risk of meningiomas and dental radiographs.17 Case-control studies are of great value, however, when cohort studies or RCTs cannot be performed due to ethical and patient safety reasons, when controversial causal claims are made by case reports and case series. A popular recent example relevant to prosthodontics is a case series on 4 patients linking zinc-containing denture adhesives to neurologic diseases.18 Multiple case-control studies would now be required to show converse results before obtaining ethical approval to perform prospective cohort studies and RCTs to examine cause-effect relationships between zinc-containing denture adhesives and neurologic diseases. Cohort studies

A cohort is a well-defined group of persons who have had a common experience or exposure and are then followed-up to determine the incidence of new diseases or

Evidence-Based Prosthodontics

health events.19 Therefore, by definition, they have the potential to establish causal relationships between exposure and disease. Historically, large cohort studies have produced powerful data that have had an impact on public health around the world. Some of these include the Framingham Heart Study examining cardiovascular disease and dietary cholesterol,20 the Physicians’ Health Study investigating aspirin and b-carotene on beta heart disease, and cancer21 and the British doctors’ cohort study examining smoking and lung cancer.22 It is understood that to have a meaningful clinical impact, cohort studies require large sample sizes and a long follow-up period. In general, there are 4 kinds of cohort studies: prospective, retrospective, nested case-control, and case-cohort study. Some examples of cohort studies with long-term follow-up, which have had a significant impact on prosthodontics, include Tallgren’s 25-year follow-up study on reduction of the residual alveolar ridges in complete denture wearers23 and a 20-year follow-up study by Douglass and colleagues24 on cephalometric evaluation of vertical dimension changes in patients wearing complete dentures. Unfortunately, such studies are uncommon because they are expensive, time-consuming, and difficult to execute without a significant loss to follow-up of patients. Therefore, short-term cohort studies have become widely popular in the prosthodontics literature, but they do not have the potential to change clinical practices or provide enough data for confident clinical decision making. Furthermore, many cohort studies in prosthodontics with longer follow-up periods lack adequate sample sizes and do not report a life table (survival) analysis. A life table (or a cohort life table) in epidemiology is defined as “a table depicting the survival data of a cohort of individuals in a clinical study or trial. This is essentially the number of items alive and under observation (not lost to follow-up) at the beginning of each year, the number surviving in each year, the number lost to follow-up each year, the conditional probability of survival for each year, and the cumulative probabilities of survival from the beginning of the study to the end of each year.”25 Life table methods subsequently allow several forms of statistical measures to be used for analysis. Some popular examples used in prosthodontics literature include Kaplan-Meier probability of survival method and the Cox proportional hazards model. Life table methods are extremely important in understanding long-term prosthodontic treatment outcomes, because they allow appreciation of attrition/loss to follow-up of samples from the beginning to the end of the study. Systematic reviews performed on observational studies that claim long-term success/survival have often exposed extremely low sample sizes remaining at the end of the study. Furthermore, different samples in a cohort study are followed-up for different time periods and, without a life table, extraction of useful data is impossible.26 Therefore, for an observational study in prosthodontics to contribute meaningful evidence to clinicians, providing a life table is paramount. Progressive Evidence Randomized controlled clinical trials

RCT is defined as “an experiment in which two or more interventions, possibly including a control intervention or no intervention, are compared by being randomly allocated to participants.”14 Because they are interventional/experimental in nature, they have a high sensitivity to prove causation and also yield quantitative data. They are regarded as the best-known method to minimize/control bias, which is defined as a systematic error or deviation in results or inferences from the truth.14 Due to these primary factors, they are often considered to provide the “highest level” of evidence in medicine. In addition to medicine, randomization is also widely popular in education,

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criminology, social work, food industry, and international development. Because of their interventional/experimental nature, RCTs are conducted only after observational and descriptive studies have shown no safety concerns for patients. In contrast to medicine and even other disciplines in dentistry, RCTs are not popular in prosthodontics for various reasons. In Harwood’s extensive analysis of 44,338 prosthodontic publications between 1966 and 2005, only 955 articles (2%) were RCTs.4 In another study by Dumbrigue and colleagues in 1999,27 only 1.7% of articles published in prosthodontic journals met the minimum criteria to be included in central register of RCTs. The same investigator in another study in 2001 noted that only 16% of RCTs published in prosthodontic journals attempted to control bias, indicating the low quality of the RCTs.28 Similarly, Jokstad and colleagues in 200229 noted that methods of randomization and allocation concealment were not described in 70% of RCTs published in prosthodontic journals. A recent study by Pandis and colleagues in 201030 compared and ranked the quality of RCTs published in top journals across 6 different specialties of dentistry. Their results showed that RCTs published in prosthodontics ranked the lowest among all specialties. All these findings demonstrate the lack of popularity of RCTs in prosthodontics. Due to the elective and expensive nature of prosthodontic treatment and associated heterogeneity, RCTs are expensive, time consuming, and not easily acquiescent for a large sample size and long-term follow-up. Furthermore, unlike other disciplines, controlling bias is challenging because randomization, double blinding, or even single blinding is difficult and several treatments involve patient input, making it difficult for allocation concealment. All of these are possible reasons for lack of popularity of RCTs in prosthodontics. It is important, however, to understand a few important elements of RCTs that are relevant to prosthodontics and scrutinize them in the published literature. Methods of randomization Randomization is defined as “the process of randomly allocating participants into one of the arms of a controlled trial.”14 Broadly, they can be classified as fixed allocation randomization or adaptive randomization and both methods have inherent advantages and disadvantages.31 Fixed allocation randomization can involve (1) a simple method, such as use of a random integer table; (2) a block method, involving blocks of integers, symbols, or alphabets (usually blocks of 4, such as ABBA); or (3) a stratified method, involving division of the members of population in homogeneous subgroups before sampling. Adaptive randomization methods include baseline adaptive randomization and response adaptive randomization. They are designed to change the allocation probabilities as the study progresses to accommodate imbalances in numbers of participants or in baseline characteristics between the two groups. They also accommodate the responses of participants to the assigned intervention.31 Another form of allocation that is not truly random is quasirandomization. This entails allocation based on a patient’s medical record number or date of birth or by simply allocating every alternate person. Such methods of allocation are easy to manipulate, leading to a selection bias. Blinding/masking Blinding in a clinical trial is defined as “the process of preventing

those involved in a trial from knowing to which comparison group a particular participant belongs. The risk of bias is minimized when, as few people as possible know, who is receiving the experimental intervention and who the control intervention. Participants, caregivers, outcome assessors, and analysts are all candidates for being blinded.”14 Due to the elective nature and the amount of control a patient has over his or her prosthodontics treatment, it is important to recognize that is difficult to perform double-blinded or triple-blinded studies.

Evidence-Based Prosthodontics

Concealment of allocation Allocation concealment in a clinical trial is defined as “the process that is used to ensure that the person deciding to enter a participant into a RCT does not know the comparison group into which that individual will be allocated.”14 It is widely accepted that the method of allocation concealment should be used as an assessment of the quality of an RCT as it has significant potential to bias the results of a study. Parallel-group trial or crossover trial Parallel-group trial or independent group trial is a popular form of RCT and is defined as “a trial that compares 2 groups of people concurrently, one of which receives the intervention of interest and one of which is a control group.”14 Some parallel trials have more than two comparison groups and some compare different interventions without including a nonintervention control group. In contrast, a crossover trial refers to “a type of clinical trial comparing 2 or more interventions in which the participants, upon completion of the course of one treatment, are switched to another.”14 A recent example of a well-designed crossover trial design in prosthodontics is a comparison between a 2-implant unsplinted overdenture, a 2-implant bar-supported overdenture, and a 4-implant bar-supported overdenture, where the participants were randomly allocated to receive the prosthesis in various orders of treatment.32 After the predetermined follow-up period, the participants were then allowed to cross over and receive the subsequent prosthesis.32 Concerns in crossover trials include the need for additional duration of the study and need for minimizing the influence of one treatment on another (called carryover effect) by allowing a pause (called a washout period).33 An additional challenge of consideration is the first-encounter bias among patients. This form of bias may lead to a nepotism and influence treatment satisfaction among patients. Single-mouth trial or split-mouth trial Single-mouth trials are the popular form of RCT in prosthodontics and involve allocation of 1 treatment of interest per mouth. Splitmouth trials refer to a type of clinical trial comparing 2 or more interventions in which the participants are subjected to random allocation of 1 treatment of half of the mouth and another treatment/no treatment of the second half of the mouth. Depending on the intervention, the mouth can be essentially split into maxilla versus mandible, right versus left, or anterior versus posterior areas. The primary objective of using a splitmouth design is to eliminate all components related to differences between subjects from the treatment comparisons and thereby reduce the error variance (noise) of the experiment and obtain a more powerful statistical test.34 Comparisons made on a within-patient basis have a disadvantage, however, in that unless a prior knowledge indicates that no carryover effects exist, reported estimates of treatment efficacy are potentially biased.34 Therefore, an important consideration is whether treatments for each side of the mouth are performed sequentially or simultaneously. An example of a split-mouth trial in prosthodontics is a comparison between all-ceramic crowns and metal-ceramic crowns between right and left sides of the mandible. In this example, although carryover effect may be less significant, all other factors need to be homogenized between the 2 treatments, such as opposing occlusion, opposing restorations, treatment tooth number, patient’s primary chewing/guiding direction, and so forth. Intention-to-treat analysis or per protocol analysis Intention-to-treat analysis and per protocol analysis are important terms that describe strategies for analyzing data from RCTs. In an intention-to-treat analysis, all participants are incorporated in the arm to which they were assigned, whether or not they received the intervention given to that arm. Intention-to-treat analysis prevents bias caused by the loss of participants,

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which may interrupt the baseline equivalence established by randomization and which may reflect nonadherence to the protocol.14 Per protocol analysis involves an analysis of the subset of participants from an RCT who complied with the protocol adequately to ensure that their data would be likely to exhibit the treatment effect. This subset may be defined after considering exposure to treatment, availability of measurements, and absence of major protocol violations. This form of analysis may be subject to bias because the reasons for noncompliance may be related to treatment.14 Systematic reviews and meta-analysis of RCTs only

An SR of the literature is defined as “a review of a clearly formulated question that uses systematic and explicit methods to identify, select, and critically appraise relevant research, and to collect and analyze data from the studies that are included in the review.”14 A meta-analysis is defined as “the use of statistical techniques in an SR to integrate the results of included studies.”14 They provide validity for published studies regarding the thoroughness of controlling systematic errors in research methods, sampling, data collection, and data analysis. SRs are significantly different from a traditional literature review, which does not necessarily have a focused question and does not have an accounted search or quantifiable data, and the review itself is subjected to author bias. Therefore, traditional literature reviews primarily serve to answer background questions, such as Who? When? Why? What? Where? and How?, and other descriptive information but do not necessarily answer a clinical question for a patient at hand. SRs help to answer foreground questions because they compare treatments and can answer clinical questions.1 The focused question for an SR usually follows the PICO format, which comprises (1) patient population of interest, (2) intervention of interest, (3) control/alternative interventions, and (4) outcome of interest. In medicine, SRs of RCTs are popularly regarded as the gold standard for evidencebased practice. This thought process may not be applicable to prosthodontics due to the well-recognized paucity of RCTs itself. The world-renowned Cochrane reviews published by the Cochrane Collaboration include SRs of only RCTs in dentistry. Cochrane reviews are distinguished from other SRs by their claim of having stringent guidelines and low risk of bias and are updated every few years. Due to stringent inclusion criteria and paucity of RCTs, a majority of Cochrane reviews in dentistry currently conclude with “lack of sufficient evidence” to recommend one treatment versus another. It is expected that with progress and better understanding of clinical research, these conclusions can be more definitive but their impact on prosthodontics is unknown at this time. Systematic reviews and meta-analysis of observational studies or all clinical studies

SRs and meta-analyses of only observational studies or including all clinical studies (both RCTs and observational studies) are widely popular in dentistry as well as in prosthodontics because such reviews are better poised to analyze more studies/ data to answer a given clinical question, in comparison to SRs of only RCTs, where data are scarce. Through an exhaustive critical analysis and data consolidation of all clinical studies, they remove the burden from a clinician to independently identify and scrutinize best studies for clinical decision making. In a study analyzing data from observational studies and RCTs, Concato and colleagues35 concluded that the results of well-designed observational studies (with either a cohort or a case-control design) do not systematically overestimate the magnitude of the effects of treatment compared with those in RCTs on the same topic. The investigators also contended

Evidence-Based Prosthodontics

that the popular belief that only RCTs produce trustworthy results and that all observational studies are misleading does a disservice to patient care, clinical investigation, and the education of health care professionals.35 It is important to recognize, however, that the risk of bias is high in SRs of observational studies compared with SRs of RCTs only. The impact of this risk of bias in clinical decision making for prosthodontics is unknown at this time. Creugers and Kreulen36 performed an SR of all SRs in prosthodontics published over a 10-year period. Two pairs of SRs were identified as dealing with comparable items (survival of fixed partial dentures and survival of single crowns). They concluded that both SRs produced similar results, but the outcomes of the evaluated SRs may be used as prognostic data and cannot be used for direct comparison of treatments.36 With the inundation of publications related to observational studies in prosthodontics, it is expected that the popularity of SRs will continue but it is important that SRs are updated periodically to include new studies and enable prospective and accurate comparison of treatment outcomes. GUIDELINES FOR REPORTING EVIDENCE

With the burgeoning publication growth in prosthodontics, it is necessary for investigators to comply with certain guidelines for reporting scientific evidence. Several consensus groups and task forces in medicine have suggested various guidelines. The common goal of all guidelines is to improve scientific reporting and ensure standardization so that they allow an accurate assessment of the presented evidence. Popular guidelines are described further. CONSORT

Consolidated Standards of Reporting Trials (CONSORT) is a popular guideline for reporting RCTs.37 A group of scientists and editors in 1996 developed this statement to improve the quality of reporting of RCTs. The objective of CONSORT is to provide guidance to investigators about how to improve the reporting of their trials and to be clear, complete, and transparent. Several medical and dental journals, including the Journal of American Dental Association, require investigators to report the findings of their RCTs to satisfy the CONSORT. The CONSORT checklist includes 37 items that cover the entire report of a trial, ranging from the study title to the source of funding. TREND

Transparent Reporting of Evaluations with Nonrandomized Design (TREND) was created in 2003.38 In contrast to CONSORT, the objective of TREND is to provide guidance to investigators to standardize and improve the reporting of studies with nonrandomized designs (cohort and case-control studies). The TREND checklist includes 22 items that cover the entire report of a study, ranging from study title to external validity. PRISMA

The objective of Preferred Reporting Items for Systematic Reviews and MetaAnalyses (PRISMA)39 is to provide guidance to investigators to standardize the reporting of SRs and meta-analyses. Initially, a group of scientists and editors in 1996 initiated a document called Quality of Reporting of Meta-analyses (QUOROM), and, in July 2007, QUOROM was changed to PRISMA. The PRISMA checklist includes 27 items that cover the entire report, ranging from abstract to the source of funding.

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PRISMA also provides a flowchart to enable investigators to describe a standardized search process. MOOSE

Meta-analysis of Observational Studies in Epidemiology (MOOSE) was created in 1997.40 The objective of MOOSE is to provide guidance to investigators to standardize the reporting of meta-analyses from nonrandomized studies. The MOOSE checklist includes 35 items, ranging from background to funding source. SORT

Strength of Recommendation Taxonomy (SORT) has emerging popularity in dentistry.41 It was developed by a group of family physicians in 2004 to classify the level of evidence for a study and provide recommendations. The objective of SORT is to provide a patient-oriented guidance to assess the quality, quantity, and consistency of evidence and allows investigators to rate individual studies or bodies of evidence. The recommendations are rated as either A, B, or C based on consistency and quality of patient-oriented evidence. AMSTAR

Assessment of Multiple Systematic Reviews (AMSTAR) was developed in 2007 as an instrument to assess the methodologic quality of SRs.42 It consists of 11 questions to analyze the quality of an SR, such as “Was a comprehensive literature search performed?” and “Was a list of studies (included and excluded) provided?” Each of these questions has 4 possible answers for the investigator: “Yes,” No,” Can’t Answer,” and “Not applicable.” This helps investigators critically analyze the quality of a published SR. LIMITATIONS OF EVIDENCE-BASED PROSTHODONTICS

There are some well-known limitations to EBD, and prosthodontics is no exception. Such limitations include applicability of research to a specific patient population, publication biases, paucity of current data, cost, and ethics. Prosthodontics is a unique specialty encompassing art, philosophy, and science and an absolute extrapolation of evidence-based concepts widely described in medicine is impossible. Establishing exceptional evidence, however, for prosthodontic treatment outcomes is paramount for the present and future of the specialty. One of the most popular criticisms for applying concepts of EBD to prosthodontics is that the information gained from clinical research may not directly answer the principal clinical question of what is best for a specific patient. This is because it is acknowledged that the homogeneity and characteristics of patients participating in clinical trials may be significantly different from those seen in dental offices. It is important to recognize, however, that EBD does not advocate absolute adoption of clinical evidence but calls for an integration of the clinical evidence along with the dentists’ clinical expertise and patient needs and preferences. EBD does not provide a cookbook that dentists must follow nor does it establish a standard of care.3 According to the ADA, the EBD process must not be used to interfere in the dentist/patient relationship nor be used entirely as a cost-containment tool by third-party payers.3 CURRENT AND FUTURE PERSPECTIVES

Compared with the traditional model of care, EBD is relatively new and, with progress in time, multiple clinical questions for which currently there is weak evidence or

Evidence-Based Prosthodontics

minimal/insufficient evidence should be resolved. Long-term survival and success of treatment, core components of the specialty of prosthodontics, is an important arena for channeling efforts and resources to help further distinguish the specialty of prosthodontics. To facilitate this process, however, it is important to establish a consensus in prosthodontics on defining the 3 core elements previously described: defining prosthodontic outcomes, duration needed for a meaningful understanding of prosthodontic outcomes, and sample size needed to make meaningful conclusions. Because prosthodontics is a unique specialty, a consensus is necessary to establish explicit guidelines for reporting of prosthodontic outcomes (suggested acronym, GROPO). Similar to numerous guidelines described in medicine, these guidelines can be exclusive to prosthodontics and ensure that investigators provide standardized reporting of their studies in order for them to be clear, complete, and transparent and allow integration of their evidence into clinical practice. In order to teach and understand evidence-based prosthodontics, clinicians need to attain new skills pertaining to computer-based knowledge systems. These skills are necessary for asking, acquiring, appraising, applying, and assessing scientific evidence for the pertinent clinical situation. Current popular resources include Web sites of PubMed/Medline, ADA Center for EBD, Cochrane Library, and Center for Evidence-Based Dentistry. The 2 popular journals dedicated to EBD are Journal of Evidence-Based Dental Practice and Evidence-Based Dentistry. Another important avenue for practicing prosthodontists is participation in practice-based research networks (PBRNs), which has gained national momentum in the United States. A dental PBRN is an investigative alliance of academic researchers and practicing dentists.43 The accord provides clinicians with an opportunity to propose or participate in research studies conducted in their own offices that address everyday issues in oral health care. These clinical studies, conducted in participating dental offices with consenting patients, help expand the profession’s evidence base and further refine care.43 Perhaps a PBRN focused on prosthodontics and/or prosthodontists can be assembled in the near future that can provide answers to specific clinical questions chosen by the specialty and for the specialty of prosthodontics. REFERENCES

1. Sackett DL, Rosenberg WM, Gray JA, et al. Evidence based medicine: what it is and what it isn’t. BMJ 1996;312(7023):71–2. 2. ADA Center for Evidence-Based Dentistry. Available at: http://ebd.ada.org/about. aspx. Accessed December 1, 2012. 3. ADA Policy on Evidence-Based Dentistry. Available at: http://www.ada.org/1754. aspx. Accessed December 1, 2012. 4. Harwood CL. The evidence base for current practices in prosthodontics. Eur J Prosthodont Restor Dent 2008;16(1):24–34. 5. Nishimura K, Rasool F, Ferguson MB, et al. Benchmarking the clinical prosthetic dental literature on MEDLINE. J Prosthet Dent 2002;88(5):533–41. 6. Russo SP, Fiorellini JP, Weber HP, et al. Benchmarking the dental implant evidence on MEDLINE. Int J Oral Maxillofac Implants 2000;15(6):792–800. 7. UCLA Department of Epidemiology. John Snow. Available at: http://www.ph.ucla. edu/epi/snow.html. Accessed December 1, 2012. 8. CDC Guidelines for Hand Hygiene in Health Care Settings. Available at: http://www. cdc.gov/mmwr/preview/mmwrhtml/rr5116a1.htm. Accessed December 1, 2012. 9. Doll R, Peto R, Boreham J, et al. Mortality in relation to smoking: 50 years’ observations on male British doctors. BMJ 2004;328(7455):1519.

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10. The Cochrane Collaboration. History. Available at: http://www.cochrane.org/ about-us/history. Accessed December 1, 2012. 11. Evidence-Based Medicine Working Group. Evidence-based medicine. A new approach to teaching the practice of medicine. JAMA 1992;268(17):2420–5. 12. Hujoel PP, DeRouen TA. A survey of endpoint characteristics in periodontal clinical trials published 1988-1992, and implications for future studies. J Clin Periodontol 1995;22(5):397–407. 13. Bidra AS, Uribe F. Successful bleaching of teeth with dentinogenesis imperfecta discoloration: a case report. J Esthet Restor Dent 2011;23(1):3–10. 14. The Cochrane Collaboration. Glossary of Terms. Available at: http://www. cochrane.org/glossary. Accessed December 1, 2012. 15. Matthews DC, Hujoel PP. A practitioner’s guide to developing critical appraisal skills: observational studies. J Am Dent Assoc 2012;143(7):784–6. 16. Owens EG, Goodacre CJ, Loh PL, et al. A multicenter interracial study of facial appearance. Part 1: a comparison of extraoral parameters. Int J Prosthodont 2002;15(3):273–82. 17. Claus EB, Calvocoressi L, Bondy ML, et al. Dental x-rays and risk of meningioma. Cancer 2012;118(18):4530–7. 18. Nations SP, Boyer PJ, Love LA, et al. Denture cream: an unusual source of excess zinc, leading to hypocupremia and neurologic disease. Neurology 2008;71(9): 639–43. 19. CDC Glossary of Epidemiology Terms. Available at: http://www.cdc.gov/excite/ library/glossary.htm. Accessed December 1, 2012. 20. Dawber TR, Meadors GF, Moore FE Jr. Epidemiological approaches to heart disease: the Framingham Study. Am J Public Health Nations Health 1951;41(3): 279–81. 21. Hennekens CH, Eberlein K. A randomized trial of aspirin and beta-carotene among U.S. physicians. Prev Med 1985;14:165–8. 22. Doll R, Hill AB. The mortality of doctors in relation to their smoking habits. BMJ 1954;1(4877):1451–5. 23. Tallgren A. The continuing reduction of the residual alveolar ridges in complete denture wearers: a mixed-longitudinal study covering 25 years. J Prosthet Dent 1972;27(2):120–32. 24. Douglass JB, Meader L, Kaplan A, et al. Cephalometric evaluation of the changes in patients wearing complete dentures: a 20-year study. J Prosthet Dent 1993; 69(3):270–5. 25. Miller-Keane encyclopedia and dictionary of medicine, nursing, and allied health. 7th edition. 2003. Available at: http://medical-dictionary.thefreedictionary.com/ life1table. Accessed December 1, 2012. 26. Bidra AS, Huynh-Ba G. Implants in the pterygoid region: a systematic review of the literature. Int J Oral Maxillofac Surg 2011;40(8):773–81. 27. Dumbrigue HB, Jones JS, Esquivel JF. Developing a register for randomized controlled trials in prosthodontics: results of a search from prosthodontic journals published in the United States. J Prosthet Dent 1999;82(6):699–703. 28. Dumbrigue HB, Jones JS, Esquivel JF. Control of bias in randomized controlled trials published in prosthodontic journals. J Prosthet Dent 2001;86(6):592–6. 29. Jokstad A, Esposito M, Coulthard P, et al. The reporting of randomized controlled trials in prosthodontics. Int J Prosthodont 2002;15(3):230–42. 30. Pandis N, Polychronopoulou A, Eliades T. An assessment of quality characteristics of randomised control trials published in dental journals. J Dent 2010;38(9): 713–21.

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31. Friedman LM, Furberg CD, DeMets DL. Fundamentals of clinical trials. 4th edition. New York: Springer; 2010. p. 97–109. 32. Burns DR, Unger JW, Coffey JP, et al. Randomized, prospective, clinical evaluation of prosthodontic modalities for mandibular implant overdenture treatment. J Prosthet Dent 2011;106(1):12–22. 33. Barnett ML, Pihlstrom BL. A practitioner’s guide to developing critical appraisal skills: interventional studies. J Am Dent Assoc 2012;143(10):1114–9. 34. Hujoel PP, DeRouen TA. Validity issues in split-mouth trials. J Clin Periodontol 1992;19(9 Pt 1):625–7. 35. Concato J, Shah N, Horwitz RI. Randomized, controlled trials, observational studies, and the hierarchy of research designs. N Engl J Med 2000;342(25): 1887–92. 36. Creugers NH, Kreulen CM. Systematic review of 10 years of systematic reviews in prosthodontics. Int J Prosthodont 2003;16(2):123–7. 37. Schulz KF, Altman DG, Moher D, CONSORT Group. CONSORT 2010 statement: updated guidelines for reporting parallel group randomised trials. J Clin Epidemiol 2010;63:834–40. 38. Des Jarlais DC, Lyles C, Crepaz N, TREND Group. Improving the reporting quality of nonrandomized evaluations of behavioral and public health interventions: the TREND statement. Am J Public Health 2004;94(3):361–6. 39. Moher D, Liberati A, Tetzlaff J, PRISMA Group. Preferred reporting items for systematic reviews and meta-analyses: the PRISMA statement. J Clin Epidemiol 2009;62:1006–12. 40. Stroup DF, Berlin JA, Morton SC, et al. Meta-analysis of observational studies in epidemiology: a proposal for reporting. Meta-analysis Of Observational Studies in Epidemiology (MOOSE) group. JAMA 2000;283(15):2008–12. 41. Ebell MH, Siwek J, Weiss BD, et al. Strength of recommendation taxonomy (SORT): a patient-centered approach to grading evidence in the medical literature. Am Fam Physician 2004;69(3):548–56. 42. Shea BJ, Grimshaw JM, Wells GA, et al. Development of AMSTAR: a measurement tool to assess the methodological quality of systematic reviews. BMC Med Res Methodol 2007;7:10. 43. Dental Practice-Based Research Network. National Institute of Dental and Craniofacial Research. Available at: http://www.nidcr.nih.gov/Research/DER/Clinical Research/DentalPracticeBasedResearchNetwork. Accessed December 1, 2012.

A review of selected dental literature on evidence-based treatment planning for dental implants: Report of the Committee on Research in Fixed Prosthodontics of the Academy of Fixed Prosthodontics Melanie R. Wood, DMD,a and Stanley G. Vermilyea, DMD, MSb College of Dentistry, The Ohio State University, Columbus, Ohio This literature review summarizes research with the aim of providing dentists with evidence-based guidelines to apply when planning treatment with osseointegrated implants. Peer-reviewed literature published in the English language between 1969 and 2003 was reviewed using Medline and hand searches. Topics reviewed include systemic host factors such as age, gender, various medical conditions, and patient habits, local host factors involving the quantity and quality of bone and soft tissue, presence of present or past infection and occlusion, prosthetic design factors, including the number and arrangement of implants, size and coatings of implants, cantilevers and connections to natural teeth, and methods to improve outcomes of implant treatment in each category. The review demonstrated that there is no systemic factor or habit that is an absolute contraindication to the placement of osseointegrated implants in the adult patient, although cessation of smoking can improve outcome significantly. The most important local patient factor for successful treatment is the quality and quantity of bone available at the implant site. Specific design criteria are provided, including guidelines for spacing of implants, size, materials, occlusion, and fit. Limitations in the current body of knowledge are identified, and directions for future research are suggested. (J Prosthet Dent 2004;92:447-62.)

n 1969, Branemark et al1 published landmark research documenting the successful osseointegration of endosseous titanium implants. Since then, these methods for surgical placement of dental implants have had a profound influence on the practice of dentistry. Implants have become the treatment of choice in many, if not most, situations when missing teeth require replacement.2-7 However, implants are not without potential problems. A tangible number of implants do not integrate or do not survive for long-term function.8-11 Complications and loss of implants can be costly, both in terms of time and financial resources. Loss of integration can be troublesome, resulting in an edentulous space more difficult to restore than prior to implant placement. The ability to reliably identify patients and conditions with greater potential for failure would be valuable. The placement of implants should not be undertaken without careful consideration of many variables, including systemic and local host factors and the design of a prosthesis. Treatment planning decisions should, whenever possible, be based on evidence-based predictions of the best long-term success. This article reviews the dental literature to provide clinically relevant guidelines for the dentist to aid in planning implant treatment. English-language peer-reviewed articles published between 1969 and 2003 were identified using Medline, as well as a hand search, and reviewed.

Private Practice, Winnipeg, Manitoba, Canada. Associate Professor and Chairman, Department of Primary Care, College of Dentistry, The Ohio State University.

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This article will review implant success and failure. For this purpose, a successful implant is defined as an osseointegrated dental implant that is successfully restored and contributing to the functional success of a dental restorative treatment or one that could be used for such purposes. An implant failure is defined as a dental implant that is not fulfilling this criterion. Early failure refers to an implant that fails to osseointegrate before second-stage surgery or uncovering of the implant. Late failure refers to loss of osseointegration or mechanical failure of an implant after second-stage surgery. Most research on the success of dental implants concentrates on the first few years after placement. Research to date suggests that when implants do fail, they tend to do so soon after placement,12 and the likelihood of failure decreases from the time of implantation through 5 years postsurgery.13 Long-term research is needed to ascertain if there is another increase in implant failure rates occurring many years after placement surgery.

SYSTEMIC HOST FACTORS Patient age Most implant patients tend to be older, as there is more likelihood of tooth loss with increasing age. However, younger patients who have missing teeth and few other restored teeth would, if conditions allowed, be ideal implant candidates. While there is no evidence for a lower age limit for the process of osseous integration to be successful, osseointegrated implants act similarly to ankylosed teeth and, therefore, lack the ability of natural teeth to compensate for skeletal bone changes in growth.14,15 While this may be acceptable THE JOURNAL OF PROSTHETIC DENTISTRY 447

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in adult patients, it is a significant factor to consider in adolescent or younger patients who are still growing.16 Possible complications of the placement of implants too early in life include the submerging of an implant into the jaw, loss of support for the implant, relocation of the implant, and potential for interference with normal growth of the jaws.15 Also, since there is more vertical growth in the posterior regions of both the maxilla and mandible during childhood and adolescence, implants placed distal to the canines present more complications.17 In the mandible, an important factor to consider is the amount of rotational facial growth.17-19 In patients with a significant rotational growth pattern, there is more growth in a posterior direction and an increased potential for posterior implants to submerge into the body of the mandible, resulting in a prosthetic infraocclusion.17-19 In patients with less rotational growth but more anterior growth, posterior mandibular implants may interfere with the normal anterior migration of natural teeth, ultimately interfering with the development of proper occlusion.15,19 In the maxilla, straight vertical growth exceeds growth in any other dimension, but the alveolar process undergoes considerable changes in all dimensions throughout the growth period.15,19,20 In addition to implant submergence, the apices of implants may become exposed in the nasal or antral cavities, and anterior implants can be lost entirely due to remodeling.15,19 Also, the growth in the midpalatal suture area should be considered. Oesterle et al15 discussed the possible restriction of transverse growth of the maxilla when a fixed implant-supported prosthesis is placed across the midpalatal suture in a growing patient. With congenitally missing permanent teeth, the advantage of waiting for growth to cease must be weighed against the reduction of ridge width over time. Ostler and Kokich21 found a 25% decrease in width of the residual ridge within 3 years of a primary molar extraction but then only 4% over the next 3 years. This loss might be better treated with ridge augmentation techniques, rather than risking the complications of placing implants too early. While most authors concur that it is necessary to wait for the growth of the jaws to conclude before placing implants in normal healthy patients, how to assess when this occurs is not clearly established. Westwood and Duncan,22 after a review of literature, suggest that clinical signs of growth, such as foot size and height, should be stable and the eruption of the permanent dentition should be complete. A rough estimate is 15 years old for women and 18 for men, although dental and skeletal maturation are better guidelines than the chronological age. Individual assessment by serial cephalometric radiographs, 1 year apart, is needed to confirm that growth has truly ceased.22 448

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At the other end of the age spectrum, there is presently no scientifically proven contraindication for the placement of implants, based solely on increasing age.23-25 Although the integration process itself is not compromised by increased age, older patients, theoretically, have potentially longer healing times, more systemic health factors, more problems adapting to new prostheses, and a decreased ability to maintain hygiene. Studies by Bryant and Zarb17,26 concerning implant outcomes in older and younger patients found no contraindication to the use of implants in older patients. The quality and quantity of available bone for implant placement and the surgical technique employed are more important factors than age. However, the older the patient, the greater the likelihood of poorer local bone conditions, so care in selecting the surgical sites is prudent.

Gender Patient gender, in the absence of any other patient differences, has not been shown to be a factor in implant failure.27

Diabetes Diabetic patients show delayed wound healing,28 increased alveolar bone loss,28 increased periodontal disease,29and increased inflammatory tissue destruction,30 all potentially complicating factors when placing implants. Also, bone and mineral metabolism are altered in diabetics,29 possibly interfering with the integration process. However, several studies have shown success with dental implants in patients with controlled diabetes.29,31-33 Fiorellini et al,29 in a study of 40 patients, found lower success rates in diabetic patients, approximately 85%, but the authors concluded that this was still a reasonable treatment outcome potential. Most of the failures were in the first year after loading. Morris et al32 studied over 650 patients with Type 2 diabetes and found only marginally more failures than with nondiabetic patients. The authors also found increased success with hydroxyapatite (HA)â&#x20AC;&#x201C;coated implants and the use of chlorhexidine mouth rinses at the time of surgery. In addition, Kapur et al34 compared diabetics who had only moderate levels of metabolic control with nondiabetic patients and also concluded that implants could be used successfully in diabetic patients. This was substantiated by Olson et al,35 who studied diabetics with implants over a 5-year period. The authors found that the duration of diabetes had an effect on implant success. Greater failure rates were found in patients who had diabetes for longer time periods. The authors theorized that just as with the increased likelihood of other microvascular complications, such as retinopathy and neuropathy, an increasing duration of diabetes could cause microvascular disturbances that might contribute to implant complications. However, no definitive length VOLUME 92 NUMBER 5

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of time associated with a diagnosis of diabetes has been established as a guideline for treatment planning.

Osteoporosis and estrogen status Osteoporosis is the loss of bone mass and density throughout the body, including the jaws. Bone metabolism is impaired and thus, theoretically, osseous integration may be more difficult to achieve. However, established systemic osteoporosis does not imply that a jaw bone is unsuitable for osseous integration,36-38 nor is it an absolute contraindication to implant therapy. While a correlation between systemic bone loss and the loss of jawbone density and quantity has been shown,39 there has not been a link established between systemic osteoporosis and implant failure. Becker et al40 quantitatively measured osteoporotic bone loss in the radius and ulna in a group of dental implant patients and found no correlation between the quantity of arm bone and implant failures. The authors suggested that visual inspection of the quality of bone at the implant site was a better indicator of implant success. Osteoporosis frequently occurs in postmenopausal women, but Dao et al,36 in studying the association between premenopausal and postmenopausal women and implant failure, did not find a higher failure rate for implants placed in women older than 50 as compared with women younger than 50 or between women and men older than 50. Minsk and Polson41 also found no correlation in older women with or without hormonal replacement therapy and implant failures. Neither of these studies differentiated between maxillary and mandibular implants. August et al42 examined jaw differences in pre- and postmenopausal women and found more failures in postmenopausal women with maxillary implants, but not mandibular implants. The authors found that postmenopausal women not taking hormone replacements had the highest failure rates. They reasoned that because osteoporosis affects trabecular bone more than cancellous bone and the maxilla has more trabecular bone content than the mandible, the maxilla is more susceptible to the effects of systemic osteoporosis. Minsk and Polson41 studied postmenopausal women undergoing hormone replacement therapy and found that the combination of postmenopausal hormone replacement and smoking did result in more implant failures. Osteoporosis has been shown to result in loss of periodontal attachment,43 but a similar loss of peri-implant tissue has not been established. For patients with extreme osteoporosis, it may be wise to be cautious with maxillary implant treatment planning and advise patients of the increased potential for negative effects resulting from smoking.

Cancer and cancer treatments Patients who have undergone tumor resection in the oral region are some of the most difficult patients to reNOVEMBER 2004

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store prosthetically and those who could benefit most from the placement of endosteal dental implants. However, there are concerns about the ability of irradiated tissue to support osseous integration and the effects of systemic chemotherapy on bone quality.

Radiation treatment The oral effects of radiation treatment include xerostomia, mucositis, hypovascularity, fibrosis, hypoxia, and most seriously, osteoradionecrosis,44-46 all potential hindrances to implant success. August et al,47 in a retrospective study, concluded that past tumoricidal radiation is no longer an absolute contraindication to implant placement, but reduced success rates, usually reported around 70%,48 can be expected, and the longterm stability of implants in irradiated bone still needs further study. To counteract the effects of radiation on bone growth and remodeling, some authors have suggested the use of hyperbaric oxygen therapy (HBO)48,49 to improve osseous integration. HBO increases the blood-totissue oxygen gradient and improves the healing capacity of irradiated tissue by stimulating capillary growth and osteogenesis.50-52 Treatment consists of breathing 100% pressurized oxygen for approximately 90 minutes for about 20 sessions presurgery and 10 postsurgery. However, many reports of successful implant placements, especially in the mandible, without HBO have demonstrated that it is not necessary for successful integration.49,53-55 Albrektsson et al56 suggest that without HBO therapy, implant surgery should be delayed for 12 months after radiation for optimal success with implant integration. However, the need for expediency of treatment for head and neck tumor patients to restore function, as well as a potential reduction in life expectancy for these patients, makes it difficult to delay treatment. Weischer and Mohr57 reported on a retrospective study that tracked irradiated patients for 9 years and also concluded that irradiation does not significantly affect osseous integration. However, the authors asserted that an important consideration was whether the definitive prosthesis was strictly implant-supported or a combination of implant- and tissue-supported. They concluded that soft tissue support should be avoided if possible, or at least minimized, due to the complications associated with poorer soft tissue healing.

Chemotherapy Chemotherapy cancer treatment causes malnutrition of osseous tissue, xerostomia, mucosal inflammation, and other complications.58 While implant integration during active chemotherapy cannot be supported by available data, Steiner et al59 reported on success in 1 patient who started chemotherapy 1 month after having implants placed. Kovacs60,61 reported on patients who had previously received courses of 3 common 449

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chemotherapeutic agents, but no radiotherapy prior to implant placement. The author concluded that there was no clinically significant detriment to the success of implants in the mandible over the study length, which averaged 3 years per patient. Research with other chemotherapeutic agents for longer periods of time and with maxillary implants is needed.

Corticosteroids Long-term use of corticosteroids generates a systemic loss of bone mass and delayed wound healing and may modify a patient’s response to bacterial infection.62 However, there are few studies documenting the effect of corticosteroids specifically on jaw bone or on the process of osseous integration in the jaws. Fujimoto et al63 studied osseointegrated implants in rabbits and found that systemic corticosteroids had less effect on the integration of titanium implants in the mandible than in skeletal bone. Also, even though the long-term use of steroids has not been shown to have a deleterious effect on gingiva and periodontal tissue adjacent to teeth,64 the effect on peri-implant tissues has not been documented. At the present time it would appear that prolonged use of corticosteroids is not a contraindication to the placement of implants.65 A more important consideration is the status of the disease process for which the corticosteroids are being administered and the prognosis for overall patient health.

Genetics and the immune system Recent research has shown that variations in the immune system and genetic factors can predispose patients to dental disease, particularly inflammation caused by bacteria and resulting periodontal disease. Logically, some of these factors may be expected to impact implant therapy. A study of implant failures by Kronstrom et al66 and a previous study by the same authors on humoral immunity67 found humoral immunity to Bacteroides forsythus and Staphylococcus aureus increased early implant failures, even in patients given antibiotics prior to implant surgery. Results suggest that patients with failing implants may be unable to mount protective serum immunoglobulin G titer levels to these pathogens. Both of the pathogens studied have been linked to dental and systemic infections. However, further study is needed to be able to predict which patients are poor implant candidates based on their systemic immunity to B forsythus and S aureus. Nosaka et al 68 studied the calcitonin receptor gene, one of the genes responsible for bone resorption, and its effect on early buccal marginal bone loss around implants. A correlation between polymorphism of the gene and buccal marginal bone loss in the mandible, but not the maxilla, between first- and second-stage implant surgery 450

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was found. Whether this was clinically significant to the long-term success of the implants was not established. Genetic markers associated with increased interleukin-1 (IL-1) production have been shown to be a factor in increased susceptibility to periodontal disease.69 Salcetti et al70 showed that patients with peri-implantitis release significantly more prostaglandin E2 and interleukin 1 compared to patients without peri-implantitis when both are exposed to the same bacterial colonization. However, Wilson and Nunn,71 in studying the relationship between the IL-1 periodontal genotype and implant loss in 27 patients, failed to find statistically significant increases in implant failures in patients who were positive for the IL-1 genotype. The authors theorized several reasons for the results, including a lesser effect of the gene on peri-implant tissue as compared with periodontal tissue, the possibility of smoking masking the action of the gene, and the limited time period of the study not being able to demonstrate a possible increase in long-term failures.

Other diseases There have been case reports of the successful placement of implants in patients with a wide variety of systemic conditions that could potentially affect biologic functions, particularly healing mechanisms. These diseases include scleroderma,72 Parkinson’s disease,73 Sjogren’s syndrome,74 HIV infection,75 multiple myeloma,76 chronic leukemia,58 pemphigus vulgaris,62 and hypohidrotic ectodermal dysplasia.77 Rather than the specific nature of the disease process, the prognosis for a patient’s long-term survival and local bone quality at the implant site are more important concerns in implant treatment planning. Also of importance is the overall health and stamina of a chronically ill patient. Patients must be able to tolerate the stressful effects of surgery and extensive restorative appointments.

The cluster phenomenon While none of the conditions discussed above are absolute contraindications to implant therapy, a combination of risk factors might be. Ekfeldt et al78 studied a group of implant patients who had multiple implant failures, in the hope of identifying patients at risk before treatment. The authors termed the occurrence of multiple implant failures the ‘‘cluster phenomenon.’’ They concluded that while no one risk factor was critical, a combination of several factors such as diabetes, osteoporosis, ongoing medications, mental depression, parafunctional jaw movements, and heavy smoking habits could provide a contraindication. However, local anatomic conditions were greater predictors of success. Weyant and Burt,12 in a study of almost 600 patients receiving implants, found that if a patient had 1 implant failure, there was a 30% chance that they would have at VOLUME 92 NUMBER 5

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least 1 other failure. These studies imply that there exists a systemic determinant of implant survival that is lacking, or a determinant of failure that is present in some patients. To date, these critical determinants of high-risk patients have not been identified or understood.

SYSTEMIC MEASURES TO IMPROVE OUTCOMES Antibiotic premedication The routine use of antibiotic premedication before dental surgery is not generally recommended,79 but there is conflicting evidence in the literature regarding the benefits of premedication for implant surgery. Some studies have shown that systemic antibiotic use prior to the surgical phase of implant placement can reduce the occurrence of infection after surgery and increase the success rates of integration.80,81 Another study found no such effect.82 However, almost all authors suggest use of presurgical antibiotics for patients with reduced host responses, such as those with diabetes, when the surgery will be lengthy and extensive.83 Dent et al,81 in an analysis of 2600 implants, found that the dosage of antibiotic is important and that the guidelines suggested by the American Heart Association for prevention of bacterial endocarditis,84 or the recommendations of Peterson,79 were most appropriate. Lambert,85 in a 3-year study on the influence of smoking on implant success, showed that antibiotic use for patients who smoke is especially important. The data showed that patients who smoked and who were not given preoperative antibiotics were 3 times more likely to have implant failures. When antibiotics were used, the authors found that failure rates for smokers and nonsmokers were the same. The reason for improved outcomes after the use of antibiotics is not known, but it is theorized that a more aseptic surgical site allows better osseous integration at a cellular level.80

Nonsteroidal anti-inflammatory drugs (NSAIDs) Certain NSAIDs are used in the treatment of periodontitis to slow the rate of alveolar bone loss. Jeffcoat et al86 studied the use of a 3-month course of NSAIDs for patients receiving dental implants and reported that 100 mg of flurbiprofen taken twice daily resulted in less bone loss in the immediate postloading period. The higher level of bone was maintained for the first year after initial surgery. The authors did not establish that the increased level of bone was clinically significant for long-term implant survival.

HABITS Smoking Patients who smoke have an increased risk for occurrence and severity of periodontal disease.87,88 Also, the NOVEMBER 2004

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deleterious effect of smoking on wound healing after tooth extraction is well documented.89-91 Therefore, the negative effect of tobacco use on implant success should be expected, and indeed this is established by several studies.92-96 Specifically, rather than affecting the process of integration, the negative effect of smoking seems to occur after second-stage surgery.85,97 Gorman et al,97 in a study of over 70 dental and medical history variables, in patients receiving over 2000 implants, found significantly more failures in smokers after second-stage surgery. After loading, differences between smokers and nonsmokers were not significant, but patients were not followed long-term. Success in smokers was increased by use of presurgical antibiotics and HA-coated implants. Lambert et al85 also conducted a longitudinal study to assess the influence of smoking in a group of patients with over 2900 endosteal dental implants. The results did not indicate significant early failure after initial surgery that was expected but showed more failures after the second stage of surgery. The authors theorized that the effect of tobacco on healing after implant placement is different from that after tooth extraction because implant wounds are closed, and the intimate adaptation of the implant to the bone tissue does not allow the same magnitude of interference in healing by the vasoconstrictive nature of nicotine. Although some smaller studies35,66 have failed to find a link between smoking and implant failures, the evidence of these larger studies is difficult to ignore. After implants are uncovered, the soft tissues around them are adversely affected by tobacco in a manner similar to that by which periodontal tissues are adversely affected.98 Smoking has been associated with an increased incidence of peri-implantitis (deep mucosal pockets around dental implants, inflammation of the peri-implant mucosa, and increased resorption of peri-implant bone).13,99 After implant uncovering, smokers tend to have faster rates of peri-implant bone loss, especially in the first year, compared with nonsmokers or patients who have stopped smoking.100 Whether this bone loss is significant for implant success has not been clearly established. In general, smoking appears to have a greater impact for maxillary implants than for mandibular implants.93,99,101 De Bruyn and Collaert,93 in a retrospective study of over 200 implants, found that prior to loading, there was a difference in success rates in smokers between maxillary and mandibular implants. Maxillary success rates were adversely affected, but those in the mandible were not. Kan et al,101 in a study of 60 patients, reported that smoking was detrimental to the success of implants placed into grafted maxillary sinuses, regardless of the amount smoked. Also, a study by Haas et al99 found peri-implantitis significantly worse in the maxilla in smokers than in nonsmokers, but this relationship was not found in the mandible. The authors 451

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theorized that mandibular treatments tended to more likely utilize implant overdentures and that, along with protection from the tongue, the prostheses provides a physical barrier to the peri-implant tissues from the local effects of smoke. In addition, smoking is known to reduce systemic bone density,94,102 and correspondingly, there is an increased incidence of poorer bone quality in the jaws of smokers. Smokers have significantly higher levels of Type IV bone.92 Bain and Moy92 found differences between moderate to heavy smokers and lighter smokers, with increased tobacco use correlated with increased implant failure rates. The authors found that the prevalence of Type IV bone was twice as high among heavy smokers as compared with nonsmokers or even light smokers. Patients who quit smoking tend to have a reduction of the effects of smoking on implant survival,85,102 but the length of time after cessation that is necessary for a significant improvement has not been sufficiently investigated. In addition to the suggestions of Gorman et al97 for use of antibiotics and HA-covered implants, success rates in smokers could be affected by the type of cover screw used. Schwartz-Arad et al95 studied the complications of smoking in patients with implants and found a greater incidence of complications in smokers who had implants with high cover screws as opposed to those with flat cover screws. However, most of the complications did not result in failures during the length of the study. Increasing the predictability of the success of dental implants is another reason why patients should be advised to stop smoking permanently. The protocol suggested by Bain102 should be followed, which advises patients to cease smoking for a minimum of 1 week prior to and at least 8 weeks after implant surgery. In Bainâ&#x20AC;&#x2122;s research with smokers who complied with this protocol, short-term implant success rates were similar to those in patients who had never smoked. However, for heavy, long-term smokers, it is less likely that bone quality will improve significantly in such a short time and patients should be informed about the reduced success rate to be expected, especially for maxillary implants.92-96

Parafunction Parafunctional habits (clenching and bruxism) have been identified as concerns in implant treatment planning due to the increased pressure on the implants, resulting in possible metal fatigue and fracture103 and possible surrounding bone loss.104 Overload caused by either improper prosthesis design or parafunctional habits is considered one of the primary causes of late-stage implant failures.105 However, Engel et al,106 in a study of 379 patients who had worn implant-retained restorations for many years, found that increased occlusal wear, usually an indicator of the severity of a bruxism parafunction, had no effect on implant integration and 452

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did not result in an increased loss of bone around implants. Rather than regarding excessive occlusal forces in patients with parafunctional habits as absolute contraindications, many authors have recommended attempting to mitigate these forces.105,107-112 Methods suggested include educating patients about habits,107 placing an increased number of implants,105 placing larger implants,108 planning the placement of implants to reduce bending overload,103 avoiding the use of cantilevers,109 using bruxism appliance therapy,110 increasing time intervals during the prosthetic restoration stages to provide more opportunity for progressive loading techniques,111 paying diligent attention to occlusal contact design,107 and using acrylic resin teeth in the prosthesis.112

The oral burn syndrome Cullen113 reported on the deleterious effects to soft tissues around implants and other dental appliances after the ingestion of hot foods and liquids. He termed this effect the oral burn syndrome. Similar to the known harmful effect of overheating bone during the placement of implants,114,115 Cullen theorized that the amount of metal in implants hastens the transfer of heat to supporting tissue and that this is a significant factor of implant complications. He suggests that patients with extensive metal dental restorations, especially patients with implants, be advised to avoid extremely highâ&#x20AC;&#x201C;temperature foods and drinks. This is a unique observation and warrants further research.

Addictions Placement of dental implants in patients with addictions to drugs and alcohol would seem to be unwise due to a patientâ&#x20AC;&#x2122;s lack of commitment to long-term health and the questionable ability to maintain implants. However, biologically, there is little evidence that chemical addictions can alter the successful integration of implants. Weyant,13 in a 5-year study of Veterans Administration implant patients, found that abuse of alcohol was a risk factor for poor implant healing and eventual failure. However, Ekfeldt et al,78 in a study of patients with multiple implant failures, found no histories of addiction to alcohol or drugs.

LOCAL HOST FACTORS Hard tissue Of necessity, there must be proper quantity and quality of bone into which dental implants are placed. The more bone in an implant site, the larger the ratio of bone to implant surface area, which increases the chances of successful integration. A larger and denser bone mass surrounding the implant may also increase postintegration resistance to forces generated by the VOLUME 92 NUMBER 5

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restoration in function. Guidelines for placement of implants aim to maximize bone-to-implant contact, within the anatomical limitations present at the site to be restored. The primary requirement is for healthy bone and secondly bone of sufficient quantity and quality to permit placement of stable implants and subsequent integration. Larger quantities of bone permit placement of longer implants. Anatomical limitations associated with the maxilla and mandible have been described by several authors.116-118 Classification systems have been developed to help determine the feasibility and predictability of implant placement.119-121 Systems are based upon jaw shape (degree of absorption, class A-E), as well as bone quality (amount of compact bone, class 1-4)116 and bone density (class A-C).120 If patients have poor bone quality and/or a lack of ridge height, grafting procedures prior to or associated with implant placement have been suggested.122-124 Alveolar ridge width must be sufficient to permit 1.5 mm of bone on both the labial and lingual surfaces for circumferential osseointegration.125 For implant restorations in the partially edentulous arch, 3 mm between the implant and an adjacent natural tooth is recommended to minimize the potential for damage to the supporting structures of the natural teeth.118 Multiple grafting techniques have been described to augment residual ridge height and width for both mandible and maxilla.126-131 However, excessive amounts of bone may require implant placement at vertical levels that could create occlusal plane interferences in the completed restoration. Ideally, some amount of resorption in the maxilla and mandible is desirable in consideration of surgical access and prosthodontic dimensional requirements. Otherwise, lack of proper occlusal clearance may significantly compromise masticatory function, phonetics, and esthetics. The amount of interarch space necessary for a restoration has not been adequately quantified. Also, balance between the amount of cortical and trabecular bone is required. Cortical bone is very dense and has a more limited blood supply that may delay the integration of implants. This may necessitate an extended time interval between surgical stages. The presence of too much loose trabecular bone may limit early stability of an implant and may also require a longer integration time. When proposed implants will be too close to large nerves, 2 possible solutions are the augmentation of the ridges to permit implant placement away from the nerve tissue or transportation of the nerve itself.118,132 However, these techniques are not without potential significant side effects, especially in the maxilla.133-135

Soft tissue As with natural teeth, it is questionable whether alveolar mucosa provides adequate soft tissue adjacent to NOVEMBER 2004

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implants or whether keratinized epithelium is necessary. A 5-year longitudinal study by Schoo and van der Veldon136 indicated that alveolar mucosa around teeth is not more likely to develop recession or inflammation than attached gingival. Similar observations were made by Krekeler et al137 concerning soft tissue around implants. Clinical observations suggest that the presence or absence of attached gingiva around implants does not appear to affect long-term soft tissue health, bone loss, or implant survival rates. However, when alveolar mucosa directly surrounds the abutments, chronic trauma as a result of muscle influence in severely resorbed jaws can cause marginal irritation.138 Han et al,139 in a case report describing a surgical technique, indicated that replacement of unattached, nonkeratinized mucosa with keratinized gingiva provided attached gingiva around implants that was healthier and more resistant to inflammation. Azzi et al140 indicated that an adequate zone of attached gingiva is necessary around anterior restorations to conceal the junction between an implant and a restoration. A comparative study by Wennstrom et al,141 focusing on implants placed in keratinized tissues, nonkeratinized tissues, and mobile soft tissues, indicated that the lack of attached masticatory mucosa around an implant did not jeopardize the maintenance of healthy soft tissues.

Infection Bacterial infection, mostly caused by gram-negative anaerobic rods and spirochetes, can cause peri-implantitis with apically progressive bone loss, resulting in loss of dental implants.142 While implant failure has not been related to the presence of any specific bacterial microorganism, the same bacteria that are associated with periodontal disease are present more frequently around failing implants.142,143 However, the presence of periodontopathic bacteria around implants is not in itself an indication of peri-implantitis.144 Genetic and environmental factors determine the severity of the host reaction. The microbial population around implants is influenced by the microbial population in the oral cavity. Mombelli et al,145 in a study of implant patients with a history of periodontal disease, found that the microflora present intraorally before implant placement determined the composition of the microflora found around the subsequently placed implants. Thus, clinicians would be prudent to ensure that patients have the most optimal periodontal health possible before implant placement. In completely edentulous patients, the microflora adjacent to implants is similar in type to that from the adjacent mucosa, which is by nature not particularly periodontopathic.146 In partially edentulous patients, the microflora present adjacent to implants tends to be the same as that adjacent to the natural dentition.145,147 Thus, the natural teeth, if they are 453

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supporting colonies of pathogenic organisms, can become reservoirs to initiate bacterial infection around implants.146,148-150 As expected, the microbial pathogens associated with periodontitis occur more commonly around implants exhibiting gingival inflammation.151 Thus, preventive periodontal therapy should be maintained after implant placement to reduce periodontal pathogens throughout the oral cavity. Quirynen et al,152 in a study of 159 partially edentulous patients, showed that a larger number of pathogenic bacteria could be found around implants when teeth were present in the same jaw as the implants, as compared with patients with teeth only in the antagonistic jaw. The authors also found that probing depths deeper than 4 mm around the teeth did not increase incidence of pathogenic bacteria around implants, but if pathogenic bacteria were present around teeth, there was a corresponding presence around implants. They also showed that the same probing depths (4 mm or greater) that support pathogens around teeth were needed around implants to support significant numbers of the same pathogens. It seems reasonable that surgeons should try to reduce final probing depths around implants by using short abutments,152 thinning the mucoperiosteal flaps, and using a surgical pack during abutment placement.119 Lee et al,153 in a study of bacteria around implants and teeth, found microbial composition differences in patients with a history of periodontal or peri-implant disease, even when no active disease was present. These patients seemed to have an increased susceptibility to growth of those organisms. The etiologic role of specific microorganisms in implant failure is still not known; thus, patients with pathogenic bacteria are not necessarily poor candidates for implants. Mengel et al,154 in a small study of implants in patients with histories of generalized chronic periodontitis and generalized aggressive periodontitis, showed success with implants in these patients 5 years after placement. Contrary to what might be expected, Lindquist et al155 showed that a patientâ&#x20AC;&#x2122;s plaque control around implants was not a significant factor affecting bone loss, unless the patient smoked. However, the authors only studied mandibular implants. They also found that the more a patient smoked, the larger the amount of measurable bone loss, but even with the increased bone loss, no smokers lost implants in the 10-year length of the study. Nonvital teeth and endodontically treated teeth may also potentially harbor bacteria that could affect implant health. There are case reports in the literature describing cross-infection from lesions of endodontic origin to implants,156,157 with some leading to loss of implants. Of particular concern are descriptions of cross-infection from teeth with endodontic treatments that were long-standing, asymptomatic, and supposedly radiographically healed. 158 Apparently, microorganisms are 454

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persistent in the periapical area, even though treatment is judged successful by all measures generally used to assess endodontic treatments. As there is no current method to test the sterility of an apex of an endodontically treated tooth, caution in placing implants adjacent to such teeth is advisable. This is especially true if an implant adjacent to an endodontically treated tooth fails and the implant is to be replaced. Thus, if an endodontically treated tooth is adjacent to an implant placement site and there is any doubt as to the sterility of the apical area, it would be prudent to endodontically retreat the tooth or even extract it. The surface characteristics of an implant can influence the amount of bacterial colonization. A rougher surface can potentially provide a better matrix upon which bacteria can grow and can afford more protection from saliva and natural muscle movement cleansing.159 The smoother an implant surface, the less the ability of bacteria to adhere. The use of mechanical scalers (plastic), bacteriocidal chemicals (chlorhexidine or iodine), and YAG lasers160 has been suggested as an appropriate counteractive measure.

Occlusal factors Natural teeth are supported by periodontal ligaments with receptors that help protect teeth and the periodontium from excessive occlusal forces that can cause trauma to the supporting bone.161,162 These neuromuscular reflexes are absent in osseointegrated implants. Clinically, a poorly developed occlusion on implant-supported restorations could have a deleterious effect on the supporting bone as well as on the accompanying prosthesis components.163 Lindquist et al,164 in a study evaluating the effects of occlusal forces on osseointegrated implants, indicated that occlusal overloading was the primary reason for bone loss around implants. Lundgren and Laurell,165 in describing occlusal forces on prosthodontically replaced dentitions, suggest the need to minimize horizontal forces caused by premature contacts or steep cusps. However, several authors have demonstrated that the magnitude or direction of occlusal forces does not appear to have an effect on the stability of supporting implants and bone. Studies employing high implant overload have shown no effect on osseous integration success in animal models.166-169 However, Isidor,170 in an animal study, demonstrated bone loss surrounding implants subjected to extremely high offaxis loading forces. With these conflicting results, the effect of occlusal loading on bone supporting implants requires further research. There may be more influence from occlusal forces on implants. Anecdotally, many clinicians have experienced the perceived consequences of the overloading of implants resulting in the loosening and fracture of components.171-174 Occlusion can contribute significantly to the maintenance of implant screws.175 Lateral excursive VOLUME 92 NUMBER 5

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contacts act as separating forces for the implant/abutment/restoration screw connection and should be avoided if possible, or at least minimized. It has been suggested that off-axis centric occlusion contacts are the most commonly overlooked causes of forces leading to the separation of implant screws. The location of these contacts should be modified, as necessary, to provide forces along the long axis of the implant.175 Thus, the occlusal scheme for an implant-supported restoration should be designed to decrease cuspal interferences, centralize forces along the long axis, and minimize lateral forces; in other words it should be like that of a similar restoration supported by a natural dentition.118

LOCAL MEASURES TO IMPROVE OUTCOMES In summary, the most effective local measures to increase implant success are to follow the guidelines previously described as to the minimum quantity and quality of bone necessary to support osseous integration and subsequent restoration. Also, as with all dental treatment, optimal oral hygiene should be maintained, both around implants and teeth, reducing potential reservoirs of periopathogenic bacteria to maximize the potential for successful treatments. Because individual response to potentially destructive bacteria is an important variable, screening for the presence of particular periodontopathic bacteria should not be used to exclude patients from implant treatment, nor should antibiotics be used universally to remove these bacteria. Research is needed to provide methods of identifying individuals at risk, so that antibacterial therapy can be used sparingly and appropriately. The use of presurgical chlorhexidine gluconate 0.12% oral rinses (Peridex; Proctor & Gamble, Cincinnati, Ohio) has been suggested by Lambert et al176 as a means to reduce infectious complications around implants. In a study of almost 600 patients receiving over 2600 implants, the authors reported that chlorhexidine rinses immediately before implant placement surgery and second-stage surgery, and twice daily for 2 weeks after the surgery, reduced the incidence of postsurgical infection by half and cut early losses of implants sixfold. Young et al177 reported that such rinses also reduce the bacterial contamination of collected bone debris to be used for augmentation procedures. As a more complete guide, in 2001 Quirynen et al178 published a comprehensive literature review discussing infectious risks for implants and methods to reduce the chances of infection.

PROSTHESIS DESIGN FACTORS Number and size of implants Theoretically, the greater the number and the larger the size of implants placed, the larger the surface area NOVEMBER 2004

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for osseous integration and the better the chance of having stable implants for restoration. The major limiting factor in this regard is the anatomy of the patient. Anatomical considerations such as the inferior alveolar canal or maxillary sinus, and local factors such as ridge height and width, may limit the placement of an ideal number or length of implants. Regarding implant length, 7 mm has been recommended as a minimum requirement.141 Winkler et al, 179 in a study of almost 300 implants, compared the survival rates of ‘‘31’’-diameter (3 mm to 3.9 mm) and ‘‘41’’-diameter (4 mm to 4.9 mm) implants with lengths of 7, 8, 10, 13, and 16 mm. Results after 36 months indicated that shorter implants had statistically lower survival rates compared to longer implants. With regard to width, the implants ‘‘31’’ mm in diameter had a lower survival rate than the ‘‘41’’ group. In addition, the shorter the implant, the greater the number of implants that should be placed for a completely implantsupported prosthesis.118 Recent observations by Worthington and Rubenstein180 have indicated that less bone height may suffice when a definitive overdenture prosthesis rather than a fixed implant-supported prosthesis is planned.

Spacing of implants There must be adequate space between implants, and between natural teeth and implants, for proper integration and tissue health. In general, there should be 3 mm between implants and between teeth and implants.118 Thus, the space needed for 2 implants of 4 mm diameter to be placed between natural teeth is 17 mm. Generally, the anterior mandible has adequate bone for placement of 4 to 6 implants.117

Cantilevers Historically, implant-supported prostheses were designed for completely edentulous patients and particularly for edentulous mandibles.163 Initial treatments involved the placement of 4 to 6 titanium implants in the mandible between the mental foramina with bilateral distal cantilevers. Generally, these cantilevered sections were limited to an arbitrary 20 mm in length on each side.118 A more recent analysis by McAlarney and Stavropoulos,181 studying the number of implants, materials, and the anterior-posterior spread of the implants, has suggested that the cantilever length desired clinically will be less than that calculated from theoretical equations. The authors studied 55 patients and determined that, if the anterior-posterior spread of the abutments is greater than 11.1 mm, then the length of a cantilever needed for adequate occlusion can generally be supported. If a significant anterior-posterior spread of the implant placements cannot be achieved, an overdenture or bar-clip–type denture should be considered, 455

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rather than a long cantilever fixed implant-supported prosthesis. Although the cantilever type of prosthesis has been an effective solution for the restoration of an edentulous mandible, it has been a much less predictable solution for the edentulous maxilla.163 The nasal cavity and maxillary sinuses often interfere with implant site selection, especially in patients with severe bone resorption.182 Adequate bone for implants may be limited to the canine eminences, lateral wall of the nasal cavity, and medial wall of the sinuses.117 Posteriorly, the maxilla presents further difficulties due to the resorption pattern, quality of bone, and proximity of the sinuses. Even with advanced surgical techniques such as immediate implant placement, ridge augmentations, and sinus lift procedures, and technically advanced implant designs, predictable outcomes of implant treatment in the posterior maxilla may be elusive. The long-term success of implants in the edentulous maxilla has been documented to be greater than 80%,183-185 but some studies have indicated significantly lower success rates in the posterior edentulous maxilla compared to the anterior areas.186,187 Even if osseous integration is a success, frequently cited complications of maxillary implantretained restorations include inadequate lip support and esthetic problems, difficulties with speech, too much space beneath the prosthesis allowing air to escape in function, or too little space compromising access for oral hygiene procedures.188-190 As a result, the use of implant-retained overdentures has been suggested in the maxilla, rather than fixed or fixed-detachable implant-supported prostheses that can be successfully used with a similar configuration of missing teeth in the mandible.191 However, research continues to elucidate techniques that provide more predictability for implant treatment in the maxilla. Angled implants placed in lieu of expensive, time-consuming, and somewhat unpredictable sinus lift or grafting procedures have been attempted.192 Aparicio et al,192 in a study of 25 patients, found that success with angled implants over an approximate 2- to 7-year period, was comparable to that with implants placed axially.

Cemented versus screw-retained restorations The decision to use screw-retained or cemented definitive restorations is largely at the discretion of the practitioner. Taylor and Agar,173 although recognizing retrievability as the major advantage of a screw-retained restoration, list 5 reasons for the use of cemented prostheses: screw openings will not interfere with esthetics or occlusion; a reduced number of components reduce the cost of cemented restorations; screw loosening is not a complication; the possibility of a more ‘‘passive fit’’ exists with a cemented restoration, since the potential strains induced in a screw-retained restoration would 456

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not be present; and the use of cemented restorations more closely follows conventional nonimplant restorations. If screw-retained prostheses are the restoration of choice, the practitioner should understand the mechanics of the use of threaded screws. An overview of implant screw mechanics has been presented by McGlumphy et al.175 The authors suggest several factors to minimize screw-loosening. Lines of occlusal forces should be along the long axis of the implants, cantilever lengths should be minimized, posterior working and nonworking contacts should be eliminated, centric occlusion contacts should be centralized along the long axis of the implant, anterior guidance should be shared with natural teeth, antirotational features of implants for single teeth should be engaged, components should be torqued to the manufacturer’s specifications, and frameworks should fit passively. Actually, these criteria should apply to cemented restorations as well, since abutments are usually screwed to the implant body beneath the cemented restoration.

Occlusal materials Traditionally, much of the rationale for selection of occlusal materials for implant restorations was based upon the original use of implant systems in the edentulous mandible. It was assumed that acrylic resin occlusal surfaces, as found in denture teeth, would provide some absorption of occlusal forces and not transmit them to bone.119 Furthermore, theoretical models indicated that resin occlusal surfaces would prevent transmission of traumatic forces to bone and not damage the implant-bone phase boundary, thus reducing the risk of implant failure.119,193 As implant-supported restorations began to be fabricated for partially-edentulous arches, demands for materials with improved physical and mechanical properties increased. Currently, metal and ceramic occlusal surfaces provide superior esthetics and wear resistance and are generally used with implantsupported restorations. In vitro studies have shown that resins reduce impact forces when compared with porcelain.112,194 However, studies simulating functioning implants have not shown significant differences in force transmission via these materials when strain gauges were placed on implants in vivo195 or in cadaver bone.196

Passivity of fit In prosthodontics in general, much effort has been expended on techniques to ensure better fitting prostheses. There are well-known sequelae of restoration misfit such as recurrent caries and loosening of the restoration. Improvements in impression techniques, die materials, investing materials, and fabrication techniques have all been suggested to improve the fit of the tooth-restoration phase boundary. Authors have assumed that misfit of implant-supported restorations could transfer strain VOLUME 92 NUMBER 5

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to the implant-bone phase boundary in sufficient amounts to cause ultimate implant failure.197-199 However, studies designed to assess the effects of the degree of misfit of an implant-supported restoration on the implant-bone phase boundary have been unable to demonstrate a negative effect of misfit on this area.200-203 From the literature, there seems to be no consensus as to the degree of misfit tolerable or the long-term effects on the implant. However, the incidence of screw loosening appears to increase if a nonpassive prosthesis framework is placed.175 It would seem prudent, therefore, to fabricate restorations that fit the implants as passively as possible.

Implant-tooth relations Prostheses supported by implants and natural teeth may offer a solution to the restoration of posterior edentulous areas in which only a single implant can be placed. The use of these combination-supported prostheses first appeared in the literature in the mid 1980’s.203-206 Authors have debated the efficacy of this design as well as whether a rigid or nonrigid connector between an abutment tooth and an implant is required.207-209 Tooth intrusion has been a frequently observed consequence of these types of combination restorations.210-212 Many theories have been forwarded to explain this, with no common agreement.213 Currently, the consensus appears to be to avoid the combination-supported restoration in favor of restorations using a single-tooth implant or placement of additional implants to retain a fixed prosthesis.213

Implant surface material In designing the implant-supported restoration, attention must be given to the interaction of the various implant component materials with each other and the oral environment. Restorations or prostheses with different alloy compositions may develop galvanic (coupled) corrosion problems when in contact.117,214,215 An in vitro investigation by Thompson et al216 demonstrated the susceptibility of implant components to galvanic-type corrosion. Lemons217 studied restoration failures as a result of galvanic corrosion properties of coupled restorative and implant materials. It is possible that if an implant receives a cast restoration that makes contact with an amalgam restoration on an adjacent tooth, there could be coupling between the amalgam and titanium or titanium alloy implant. However, implants coupled with noble alloys of gold, palladium, and silver show little susceptibility to corrosion.216,218 Given the numbers of implant-supported restorations and the relative paucity of reports of untoward events concerning corrosion, this may not be of current clinical significance. The different implant systems available present several types of surface treatments with the goal of maximizing bone-implant contact. Some of the available NOVEMBER 2004

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treatments are machining, etching, airborne-particle abrasion with soluble particles, titanium plasma spraying (TPS), and hydroxyapatite (HA) coating. Studies designed to examine the relative merits of these treatments have produced mixed results. A study by London et al219 evaluated the bone contact percentage with several different surface coatings on implants. The authors found that HA coatings offered no advantage as compared to titanium and that rough HA-coated surfaces scored similar to rough TPS surfaces in terms of a bone-contact percentage. A ‘‘dual etched’’ titanium surface had the highest percentage of bone contact in this study. However, Novaes et al, 220 in an animal study, found that any of the studied treatments that added roughness to the implant surface (HA-coating, TPS, airborne-particle abrasion) showed bone contact percentages higher than that of a machined titanium surface. Whether this is a significant factor to long-term implant success remains to be established.

DESIGN FEATURES TO IMPROVE OUTCOMES To minimize potential problems during the restorative phase, it is imperative that the dentist restoring the implants, after consultation with appropriate specialists, be primarily responsible for the treatment planning. This is a challenging responsibility, especially in light of the lack of rigorous scientific principles to guide a practitioner with prosthesis design and the catastrophic nature of implant failure. Thus, as with any prosthodontic restoration, meticulous attention must be given to treatment planning. Subsequent to the customary medical and dental history analysis, intraoral and extraoral examination, and radiographic analysis, diagnostic casts should be made. These casts, along with a facebow transfer and occlusal registration, are essential for treatment planning and restoration design. Also, properly oriented diagnostic casts are needed to evaluate the remaining dentition, residual bone, and maxillomandibular relationships.101,125

FUTURE RESEARCH In the past, principles and concepts, often empirical in nature, for the treatment of natural teeth have been extrapolated to apply to treatment with dental implants. In the current ‘‘evidence-based’’ environment, this is no longer acceptable. Further research is needed to provide better answers to the ‘‘how’’ and ‘‘why’’ of successful implant-supported restorations. New cellular and subcellular techniques may help develop methods to increase the rate of osseous integration, reduce the healing time, and provide compelling evidence for the immediate loading of implants at the time of placement. More study is needed on the role of antibiotics during implant therapy. More knowledge about host immunity 457

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factors could provide invaluable predictors of treatment success. As smoking is identified as one of the major controllable factors for implant failure, more definitive smoking cessation protocols regarding length of time of cessation would be helpful. The appropriate amount of time to wait after an infection in an implant site before implant placement has to be determined. Longer-term research is needed to follow different treatment techniques in different patient situations, specifically to identify the so-called ‘‘cluster phenomena’’ factors. Improved methods to assess local bone quality prior to actual surgery are necessary. More reliable methods of augmenting bone need to be identified. The effects of design variables, such as occlusal load bearing and differences in surface coatings, require quantification and documentation in long-term studies. It is hoped that research into new fabrication and surgical techniques will reduce the costs of implant-supported prostheses and make this treatment option more widely available. This article has not discussed the issue of esthetic restoration with implants. Because of the inherent objectiveness of evaluating esthetics, there is a lack of quantifiable evidence-supported guidelines regarding esthetics. Future research could aim to quantify the area of esthetics so that such guidelines could be established. Finally, clinicians need the results of randomized, controlled clinical trials for evidence-based decisionmaking. However, these types of studies are difficult to design and are time-consuming and expensive. Furthermore, with the rapid deployment of commercial implant products, an implant may be obsolete by the time a rigorous study is completed. However, after more than 20 years of implant therapy, basic science research should be able to provide information on which products should be selected for meaningful clinical trials. Until this can be done, the design of implant restorations will be based on less evidence than is desirable.

SUMMARY Treatment planning for the placement and restoration of osseointegrated dental implants involves the consideration of many variables, including systemic and local host factors and the design of the prosthesis. This literature review provides a summary of evidence-based principles to guide the dentist in making planning decisions. Limitations in current knowledge of this topic and directions for future research were also suggested. REFERENCES 1. Branemark PI, Adell R, Breine U, Hansson BO, Lindstrom J, Ohlsson A. Intra-osseous anchorage of dental prostheses. I. Experimental studies. Scand J Plast Reconstr Surg 1969;3:81-100. 2. Mericske-Stern R. Overdentures with roots or implants for elderly patients: a comparison. J Prosthet Dent 1994;72:543-50. 3. Misch CE. Endosteal implants for posterior single tooth replacement: alternatives, indications, contraindications, and limitations. J Oral Implantol 1999;25:80-94.

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4. Zarb GA, Schmitt A. The edentulous predicament I: A prospective study of the effectiveness of implant-supported fixed prostheses. J Am Dent Assoc 1996;127:59-65. 5. Mericske-Stern RD, Taylor TD, Belser U. Management of the edentulous patient. Clin Oral Implants Res 2000;11:108-25. 6. Attard N, Zarb GA. Implant prosthodontic management of posterior partial edentulism: long-term follow-up of a prospective study. J Can Dent Assoc 2002;68:118-24. 7. Heydecke G, Boudrias P, Awad MA, De Albuquerque RF, Lund JP, Feine JS. Within-subject comparisons of maxillary fixed and removable implant prostheses: Patient satisfaction and choice of prosthesis. Clin Oral Implants Res 2003;14:125-30. 8. Esposito M, Hirsch JM, Lekholm U, Thomsen P. Biological factors contributing to failures of osseointegrated oral implants. (I). Success criteria and epidemiology. Eur J Oral Sci 1998;106:527-51. 9. Goodacre CJ, Kan JY, Rungcharassaeng K. Clinical complications of osseointegrated implants. J Prosthet Dent 1999;81:537-52. 10. Bragger U, Aeschlimann S, Burgin W, Hammerle CH, Lang NP. Biological and technical complications and failures with fixed partial dentures (FPD) on implants and teeth after four to five years of function. Clin Oral Implants Res 2001;12:26-34. 11. Quirynen M, De Soete M, van Steenberghe D. Infectious risks for oral implants: a review of the literature. Clin Oral Implants Res 2002;13:1-19. 12. Weyant RJ, Burt BA. An assessment of survival rates and within-patient clustering of failures for endosseous oral implants. J Dent Res 1993; 72:2-8. 13. Weyant RJ. Characteristics associated with the loss and peri-implant tissue health of endosseous dental implants. Int J Oral Maxillofac Implants 1994;9:95-102. 14. Guckes AD, Brahim JS, McCarthy GR, Rudy SF, Cooper LF. Using endosseous dental implants for patients with ectodermal dysplasia. J Am Dent Assoc 1991;122:59-62. 15. Oesterle LJ, Cronin RJ Jr, Ranly DM. Maxillary implants and the growing patient. Int J Oral Maxillofac Implants 1993;8:377-87. 16. Bryant SR, Zarb GA. Osseointegration of oral implants in older and younger adults. Int J Oral Maxillofac Implants 1998;13:492-9. 17. Bryant SR. The effects of age, jaw site, and bone condition on oral implant outcomes. Int J Prosthodont 1998;11:470-90. 18. Cronin RJ Jr, Oesterle LJ, Ranly DM. Mandibular implants and the growing patient. Int J Oral Maxillofac Implants 1994;9:55-62. 19. Cronin RJ Jr, Oesterle LJ. Implant use in growing patients. Treatment planning concerns. Dent Clin North Am 1998;42:1-34. 20. Bjork A, Skieller V. Growth of the maxilla in three dimensions as revealed radiographically by the implant method. Br J Orthod 1977;4: 53-64. 21. Ostler MS, Kokich VG. Alveolar ridge changes in patients congenitally missing mandibular second premolars. J Prosthet Dent 1994;71: 144-149. 22. Westwood RM, Duncan JM. Implants in adolescents: a literature review and case reports. Int J Oral Maxillofac Implants 1996;11:750-5. 23. Kondell PA, Nordenram A, Landt H. Titanium implants in the treatment of edentulousness: influence of patient’s age on prognosis. Gerodontics 1988;4:280-4. 24. Meijer HJ, Batenburg RH, Raghoebar GM. Influence of patient age on the success rate of dental implants supporting an overdenture in an edentulous mandible: a 3-year prospective study. Int J Oral Maxillofac Implants 2001;16:522-6. 25. Ochi S, Morris HF, Winkler S. Patient demographics and implant survival at uncovering: Dental Implant Clinical Research Group Interim Report No. 6. Implant Dent 1994;3:247-51. 26. Bryant SR, Zarb GA. Osseointegration of oral implants in older and younger adults. Int J Oral Maxillofac Implants 1998;13:492-9. 27. Smith RA, Berger R, Dodson TB. Risk factors associated with dental implants in healthy and medically compromised patients. Int J Oral Maxillofac Implants 1992;7:367-72. 28. Devlin H, Garland H, Sloan P. Healing of tooth extraction sockets in experimental diabetes mellitus. J Oral Maxillofac Surg 1996;54: 1087-91. 29. Fiorellini JP, Chen PK, Nevins M, Nevins ML. A retrospective study of dental implants in diabetic patients. Int J Periodontics Restorative Dent 2000;20:366-73. 30. Iacopino AM. Diabetic periodontitis: possible lipid-induced defect in tissue repair through alteration of macrophage phenotype and function. Oral Dis 1995;1:214-29.

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188. Desjardins RP. Prosthesis design for osseointegrated implants in the edentulous maxilla. Int J Oral Maxillofac Implants 1992;7:311-20. 189. Keller EE, Van Roekel NB, Desjardins RP, Tolman DE. Prosthetic-surgical reconstruction of the severely resorbed maxilla with iliac bone grafting and tissue-integrated prostheses. Int J Oral Maxillofac Implants 1987;2: 155-65. 190. Taylor TD. Fixed implant rehabilitation for the edentulous maxilla. Int J Oral Maxillofac Implants 1991;6:329-37. 191. DeBoer J. Edentulous implants: overdenture versus fixed. J Prosthet Dent 1993;69:386-90. 192. Aparicio C, Perales P, Rangert B. Tilted implants as an alternative to maxillary sinus grafting: a clinical, radiologic, and periotest study. Clin Implant Dent Relat Res 2001;3:39-49. 193. Skalak R. Biomechanical considerations in osseointegrated prostheses. J Prosthet Dent 1983;49:843-8. 194. Davis DM, Rimrott R, Zarb GA. Studies on frameworks for osseointegrated prostheses: Part 2. The effect of adding acrylic resin or porcelain to form the occlusal superstructure. Int J Oral Maxillofac Implants 1988; 3:275-80. 195. Hobkirk JA, Psarros KJ. The influence of occlusal surface material on peak masticatory forces using osseointegrated implant-supported prostheses. Int J Oral Maxillofac Implants 1992;7:345-52. 196. Cibirka RM, Razzoog ME, Lang BR, Stohler CS. Determining the force absorption quotient for restorative materials used in implant occlusal surfaces. J Prosthet Dent 1992;67:361-4. 197. Jemt T, Lekholm U. Measurements of bone and frame-work deformations induced by misfit of implant superstructures. A pilot study in rabbits. Clin Oral Implants Res 1998;9:272-80. 198. Millington ND, Leung T. Inaccurate fit of implant superstructures. Part 1: Stresses generated on the superstructure relative to the size of fit discrepancy. Int J Prosthodont 1995;8:511-6. 199. Roberts WE, Smith RK, Zilberman Y, Mozsary PG, Smith RS. Osseous adaptation to continuous loading of rigid endosseous implants. Am J Orthod 1984;86:95-111. 200. Carr AB, Gerard DA, Larsen PE. The response of bone in primates around unloaded dental implants supporting prostheses with different levels of fit. J Prosthet Dent 1996;76:500-9. 201. Gotfredsen K, Berglundh T, Lindhe J. Bone reactions adjacent to titanium implants subjected to static load. A study in the dog (I). Clin Oral Implants Res 2001;12:1-8. 202. Hurzeler MB, Quinones CR, Kohal RJ, Rohde M, Strub JR, Teuscher U, et al. Changes in peri-implant tissues subjected to orthodontic forces and ligature breakdown in monkeys. J Periodontol 1998;69: 396-404. 203. Jemt T, Book K. Prosthesis misfit and marginal bone loss in edentulous implant patients. Int J Oral Maxillofac Implants 1996;11: 620-5. 204. Babbush CA, Kirsch A, Mentag PJ, Hill B. Intramobile cylinder (IMZ) two-stage osteointegrated implant system with the intramobile element (IME): part I. Its ratinale and procedure for use. Int J Oral Maxillofac Implants 1987;2:203-16. 205. English CE. Biomechanical concerns with fixed partial dentures involving implants. Implant Dent 1993;2:221-42. 206. Kirsch A, Mentag PJ. The IMZ endosseous two phase implant system: a complete oral rehabilitation treatment concept. J Oral Implantol 1986;12:576-89.

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207. Astrand P, Borg K, Gunne J, Olsson M. Combination of natural teeth and osseointegrated implants as prosthesis abutments: a 2-year longitudinal study. Int J Oral Maxillofac Implants 1991;6:305-12. 208. Cohen SR, Orenstein JH. The use of attachments in combination implant and natural-tooth fixed partial dentures: a technical report. Int J Oral Maxillofac Implants 1994;9:230-4. 209. Ericsson I, Lekholm U, Branemark PI, Lindhe J, Glantz PO, Nyman S. A clinical evaluation of fixed-bridge restorations supported by the combination of teeth and osseointegrated titanium implants. J Clin Periodontol 1986;13:307-12. 210. Sheets CG, Earthmann JC. Tooth intrusion in implant-assisted prostheses. J Prosthet Dent 1997;77:39-45. 211. Schlumberger TL, Bowley JF, Maze GI. Intrusion phenomenon in combination tooth-implant restorations: a review of the literature. J Prosthet Dent 1998;80:199-203. 212. Naert IE, Duyck JA, Hosny MM, Van Steeberghe D. Freestanding and tooth-implant connected prostheses in the treatment of partially edentulous patients. Part I; An up to 15-years clinical evaluation. Clin Oral Implants Res 2001;12:237-44. 213. Pesun IJ. Intrusion of teeth in the combination implant-to-natural-tooth fixed partial denture: a review of the theories. J Prosthodont 1997;6: 268-77. 214. Bergman M, Ginstrup O, Nilner K. Potential and polarization measurements in vivo of oral galvanism. Scand J Dent Res 1978;86:135-45. 215. Inovay J, Banoczy J. Role of electrical potential differences in the etiology of chronic diseases of the oral mucosa. J Dent Res 1961;40:884-90. 216. Thompson NG, Buchanan RA, Lemons JE. In vitro corrosion of Ti-6Al-4V and type 316L stainless steel when galvanically coupled with carbon. J Biomed Mater Res 1979;13:35-44. 217. Lemons JE. Dental implant retrieval analyses. Int J Oral Implantol 1988; 5:41-5. 218. Grosgogeat B, Reclaru L, Lissac M, Dalard F. Measurement and evaluation of galvanic corrosion between titanium/Ti6A14V implants and dental alloys by electrochemical techniques and auger spectrometry. Biomaterials 1999;20:933-41. 219. London RM, Roberts FA, Baker DA, Rohrer MD, Oâ&#x20AC;&#x2122;Neal RB. Histologic comparison of a thermal dual-etched implant surface to machined, TPS, and HA surfaces: bone contact in vivo in rabbits. Int J Oral Maxillofac Implants 2002;17:369-76. 220. Novaes AB Jr, Souza SL, de Oliveira PT, Souza AM. Histomorphometric analysis of the bone-implant contact obtained with 4 different implant surface treatments placed side by side in the dog mandible. Int J Oral Maxillofac Implants 2002;17:377-83. Reprint requests to: DR MELANIE WOOD 380 - 500 PORTAGE AVE WINNIPEG, MANITOBA, R3C 3V4 FAX: 204-783-3244 E-MAIL: melaniew@mb.sympatico.ca 0022-3913/$30.00 Copyright Ă&#x201C; 2004 by The Editorial Council of The Journal of Prosthetic Dentistry doi:10.1016/j.prosdent.2004.08.003

VOLUME 92 NUMBER 5

Need for evidence-based practice in prosthodontics James D. Anderson, DDS, MScDa University of Toronto, Toronto, Canada Statement of problem. Patients, their insurers, the courts, and the scientific community are demanding more evidence to support the effectiveness of health care strategies.

Purpose. This article describes evidence-based practice, its origins, and value as a way of addressing the demand for evidence of treatment effectiveness in maxillofacial prosthetics. Material and methods. A limited review of maxillofacial prosthetics literature was performed using Medline over the years 1966 to 1998. The retrieved articles were classified by methodologic design and assessed for the strength of their evidence. Results. Focused and speedy (but not necessarily comprehensive) literature searching methods are available. Critical appraisal skills are available and needed to assess the quality of evidence in support of a treatment and to maintain clinical skills. Conclusion. With appropriate skills and the availability of literature searching hardware and software, evidence-based practice is a powerful means for the practitioner to establish the effectiveness of individual patient treatment, and to prevent the diminution of clinical skills over the course of a career. These skills should be included in training programs. (J Prosthet Dent 2000;83:58-65.)

CLINICAL IMPLICATIONS The results of this literature review and critique indicate that clinical judgment is needed to determine the applicability of external evidence to the patient. Patients will then receive treatment that is supported by systematic evidence.

ealth care providers devote considerable time and energy to the careful application of knowledge to their patients. A scrupulous reading of the journals and frequent attendance at continuing education courses follows many years of study in school. All of this knowledge is supplemented by learning from mistakes and consulting respected colleagues. Therefore, it is not surprising that evidence-based practice appears to be a natural evolution in the application of the accumulated knowledge and experience of a practitioner. However, this model of practice is no longer enough. Patients and insurers demand assurance of treatment effectiveness. In addition, litigation is increasing and the availability of free information is beginning to render obsolete the old legal standard of “commonly accepted practice.” Therefore, the traditional model is not evidence-based practice by the modern definition. The purpose of this article is to describe evidencebased practice, its origins, and value as a way of addressing the demand for evidence of treatment effectiveness Presented before the American Academy of Maxillofacial Prosthetics, 46th annual meeting, Victoria, British Columbia, October 1998. aCraniofacial Prosthetic Unit, Toronto-Sunnybrook Regional Cancer Center. 58 THE JOURNAL OF PROSTHETIC DENTISTRY

in prosthodontics, using the literature in maxillofacial prosthetics as an illustration.

EVIDENCE-BASED PRACTICE (EBP)— WHAT IS IT? The modern concept of evidence-based practice (or evidence-based medicine) was introduced by David Sackett et al,1 and they defined it as “…the conscientious, explicit and judicious use of current best evidence in making decisions about the care of individual patients. The practice of evidence-based medicine means integrating individual clinical expertise with the best available external clinical evidence from systematic research.”1 What follows is an application of their notion to the practice of maxillofacial prosthetics. The traditional model of practice (Fig. 1) is an exchange between the patient and provider. The patient supplies a complaint and the provider, considering all the factors, supplies advice, a decision, or treatment. The provider brings to bear on the decision all the background (s)he can remember in the available time. Where a definitive answer is not available, a working plan is provided, based on knowledge of pathophysiological processes or memory of similar clinical problems. The new model (Fig. 2) begins as before, with a patient problem, and if there is any uncertainty about VOLUME 83 NUMBER 1

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Fig. 1. Traditional model of practice.

the explicit answer, the problem is converted (following certain guidelines) into an answerable question. The second step is to isolate quickly and efficiently the best current literature that purports to answer the question. The third step is to critically appraise that literature for its validity and applicability to the present patient. Finally, the evidence is integrated with everything else that is known about the patient’s condition to return with a treatment decision. This new paradigm assumes that all structures in the previous model are still in place. An interpretation of the complaint is still needed; the practitioner’s experience cannot be discounted; and the patient’s surrounding circumstances still need to be considered. However, it adds a mechanism for finding and critically appraising the most current and best evidence that is keyed to the present patient problem, and for integrating it into treatment decisions. What makes it revolutionary is the work habit it requires, the confidence one derives from the results and, importantly, the capacity for preventing a decline in skills throughout the career. Therefore, it supplants nothing. This is important, because one could not suggest that patient treatment should be driven by the literature alone, absent clinical judgment, any more than one could suggest that clinical judgment should ignore the evidence.

EVIDENCE-BASED PRACTICE—WHAT IT ISN’T Journal reading, as performed today, takes the form of what could be called “browse mode,” perusing subscribed journals each month and reading the more interesting articles in a little more detail. The longstanding evidence revealing large variation in dentists’ treatment behaviors contradicts the argument that EBP is provided on the basis of browse mode reading. Fifteen years ago, Elderton et al2 pointed out the wide variation in dentists’ treatment plans. Since then, further documentation has shown that there has been little improvement.3,4 Within maxillofacial prosthetics, the vast array of clinical reports detailing various treatment methods suggests that there is considerable disagreement among providers on the most effective options. They cannot all be superior. On the other hand, EBP requires a search of the available literature and critical reading to answer a speJANUARY 2000

Fig. 2. Model of evidence-based practice.

cific question posed by the patient’s condition. This is reading in “focused mode.” It builds a library of answers to questions encountered in everyday practice, ready for the next time the issues come up. It should not be suggested, however, that EBP will reveal one best way of doing things and all others are necessarily second best. This is where the clinical judgment comes in and is indispensable. EBP is intended to be used in conjunction with an assessment of the applicability of the external evidence to the present patient’s predicament. This includes other threats to the patient and his/her values, priorities, and resources. Advocates of EBP will be among the first to support their critics who suggest that EBP will lead to restrictive practice. EBP is intended to inform, but not supplant, clinical judgment. With the rising cost of health care, insurers and governments are becoming less and less tolerant of the variation in diagnoses and treatments offered to patients and the attendant costs. As the variation becomes better documented, alarm bells ring and cost containment strategies appear. Systematic evidence for the effectiveness of certain treatments could then become a convenient “blunt instrument” for insurers to limit coverage. However, the thoughtful evidencebased practitioner will choose the most effective treatment based on systematic evidence, modified by clinical judgment, and that could just as likely be less expensive rather than more. There should be nothing to fear from regulatory agencies that seek to use properly designed clinical evidence to determine reimbursement practices for the most effective treatments. With the additional steps necessary to do EBP, one might suspect that it is a luxury available only to those who practice in institutional settings where the pace of practice may be slower or there is more flexibility in time allocation. There is no doubt that some time needs to be given to this activity, but it need not be any 59

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Table I. Selected of journals of prosthodontic interest searched in Medline

Table II. The steadily increasing number of articles per year in the selected journals

General • Journal of the American Dental Association • Journal of Dental Research Prosthodontic • Clinical Oral Implants Research • International Journal of Oral & Maxillofacial Implants • International Journal of Prosthodontics • Journal of Prosthetic Dentistry • Journal of Prosthodontics

Range of years 66-75 Number of years/range 10 Number of articles/range 6838 Articles per year 684

more than is presently given to browse mode reading. Practitioners with a computer and access to the Web are fully equipped to develop their skills in searching the available literature and to initiate EBP.

76-84 9 6891 766

85-89 5 4091 818

90-94 5 4370 874

95-98 3± 2762 ≈921

Table III. The introduction of new and stronger research designs found in the selected journals Range of years 66-75 Number of articles 6838 Number of RCTs 0 % RCTs 0 Number of critical reviews 0 % critical reviews 0

76-84 6891 8 0.1 0 0

85-89 4091 23 0.5 3 0.075

90-94 4370 58 1.4 3 0.075

95-98 2762 53 2.3 5 0.2

WHY SHOULD WE GET INTO EBP? There are several reasons for being attentive to this new paradigm. First, the explosion in the volume of prosthodontic literature makes it virtually impossible to keep up with current reading (Tables I and II). Subscribing to every journal and attempting to read every issue is not only impossible, but is also unfocused and therefore wasteful of time. This kind of reading (in “browse mode”) offers no connection to current problems, except by coincidence, and therefore has less chance of “sticking in the mind” of the reader. Second, the scientific rigor shown in the clinical dental literature is changing for the better, albeit gradually, with the introduction of new research designs (Table III). The increasing use of the randomized trial and more emphasis on research methodology has resulted in much greater strength of evidence. Similarly, the introduction of the systematic overview and metaanalysis of multiple, properly designed studies has improved our ability to draw conclusions from these studies that individually had too small a sample size to reach a definitive conclusion. The result then is an improvement and a much broader range in the strength of evidence available to the reader. Third, if one cannot keep up with the reading and if one cannot discriminate between weak and strong evidence, how can one prevent themselves from “falling behind”? There is evidence from both medicine5,6 and dentistry7,8 that clinical skills deteriorate with increasing years since graduation. No educational model could be found in dentistry that provides evidence of preventing a slip into substandard practice. However, EBP has been shown to prevent such a slide in medicine. McMaster University in Hamilton, Ontario, has developed a problem-based evidence-based curriculum that has been copied by many medical schools around the world. McMaster graduates with EBP skills maintained their clinical skills up to 15 years after graduation, 60

whereas graduates of a traditional program, lacking EBP skills, showed a gradual decline.9 With the rapid change of pace in the practice of dentistry, there is no reason to think that maintaining these clinical skills over the course of a career should be any easier. There is an alternative strategy for keeping pace, namely, continuing education. Unfortunately, the evidence in support of effective transfer of continuing education content to practice is mixed. In a study of the effect of a prosthodontic video CE course sent to general practitioners, 40% indicated that they would leave all partial denture design decisions to the technician on at least some occasions.10 The authors concluded that, although the program had been well received and had produced changes in intention, there was less objective evidence of actual change in practice.10 One might ask then, if EBP is any different, and does it have any impact on delivered service? Here, evidence is available from the medical specialties, because no test of it could be found in dentistry. There has been considerable progress in internal medicine, the discipline where EBP got its start.11 A British study showed that fully 82% of internal medicine patients at an evidence-based center received treatment for which documented evidence of effectiveness exists. In another study, 47% of literature searches on patient problems affected the clinical decisions, though the information revealed by the searches was rather scanty.12 Another review showed improved physician performance and patient outcome when a computer-based clinical decision support system was used.13 These studies offer a compelling suggestion that use of EBP directly affects patient treatment. After considering these issues, it should be evident that one can hardly afford not to develop the skills of EBP. Further, those in teaching institutions should include it among the skills that are taught. New graduates should expect to be given the skills to become VOLUME 83 NUMBER 1

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obvious. If the provider elects not to proceed on the basis of conjecture, a general search of the literature may reveal some clues. However, this approach is unfocused and therefore has the potential to waste time. It could result in looking through too many articles that touch on the problem and may be interesting, but are not directly helpful. The first step then, in the cycle of EBP is to convert the patient complaint into a structured answerable question (Fig. 3, A through C).

Components of a question

The patient represents a group of people in similar circumstances, so the first component of the question defines the population of interest. This definition may take the form of age or sex limits, or patients with a particular history, clinical problem, or comorbid condition. The second component of the question describes what is happening to the patient—a maneuver. In maxillofacial prosthetics, because diagnostic and prognostic issues are less common, the maneuver is often a treatment. It could, however, take the form of a harmful exposure, such as radiation or smoking. A third component, in the form of an alternative maneuver for comparison, will focus the search further. Finally, the fourth component of the question is the outcome being sought, and here it is important to be specific. Prosthesis survival, freedom from pain, and chewing efficiency are examples. Articles that explore the same type of patients, exposed to the same treatments, but look at outcomes not of interest to the patient “in your chair,” are not helpful except as background information that may lead to other questions. This component therefore helps to focus the search and quickly rule out irrelevant articles.

Getting the evidence

C Fig. 3. A, Examples of first component of one question. B, Examples of second and third components of one question. C, Examples of fourth component of one question.

independent lifelong learners amid the avalanche of useful and useless information available to them.

THE PROBLEM AND THE QUESTION EBP begins and ends with the patient. The patient’s chief complaint may raise questions in the mind of the practitioner for which a specific answer is not readily JANUARY 2000

Once the question is articulated, the best available evidence must be assembled as efficiently as possible. There are several options. One can ask a colleague what (s)he would do in the circumstances. This strategy is certainly efficient. However, it leaves open the possibility of the blind leading the blind. One can also consult textbooks and other notes that may have accumulated in personal libraries. Given the difficulty of keeping a library up to date, it is unlikely it will contain the most current information on the question. Or one may look to the literature for the most current and best information on the subject. Electronic databases and searching software available on the World Wide Web make this a viable option that offers the promise of great efficiency.

LIMITATIONS OF ELECTRONIC LITERATURE SEARCH Journals With databases like Medline being so accessible, comprehensive, and convenient to use, it is easy to get 61

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Table IV. A selection of databases of potential interest in maxillofacial prosthetics Database

Medline HealthSTAR CancerLit Science Citation Index EMBase (Exerpta Medica) Engineered Materials Abstracts

Coverage

Health and biologic sciences Health services delivery, technology admin, research policy, insurance, economics, legal Cancer therapy and carcinogenesis Medicine, physical and biologic sciences Pharmacologic and biomedical disciplines Polymers, ceramics, composites

Table V. Critical appraisal questions for an article about therapy • Are the Results of the Study valid? 1. Was the assignment of patients to treatments randomized? 2. Were all patients who entered the trial properly accounted for and attributed at its conclusion? 3. Were patients, their clinicians, and study personnel blinded to treatment? 4. Were the groups similar at the start of the trial? 5. Aside from the experimental intervention, were the groups treated equally? • What were the results? 1. How large was the treatment effect? 2. How precise was the estimate of the treatment effect? • Will the results help me in caring for my patients? 1. Can the results be applied to my patient care? 2. Were all clinically important outcomes considered? 3. Are the likely treatment benefits worth the potential harms and costs? Guyatt GH et al. JAMA 1993;270(21):2598-601. Guyatt GH et al. JAMA 1994;271(1):59-63.

lulled into the notion that, if the evidence being sought cannot be found in Medline, then it does not exist. This is not the case. Although Medline offers the longest history among electronic databases, it is far from the only source of information. There are many others that should not be ignored, depending on the subject being explored (Table IV).

Selective indexing and delay in indexing Another unavoidable problem that limits the effectiveness of electronic searching is the delay between the publication date and the date the article is posted into the database. Not surprisingly, it is a point of pride among database suppliers to compress this time, but there will be some delay, in some cases, by as much as a year. The National Library of Medicine ranks the journals it indexes, giving speedy treatment to some journal titles at the expense of others (Walker SR. Oral communication, 1998).

Second-guessing the indexers Any exercise in isolating the relevant literature is an 62

Journals

Years

3600

1966

N/A 200 5300 3500 2000

1975 1983 1993 1980 1986

exercise in second-guessing the indexers. Authors, editors, or indexers set down a list of keywords, or MeSH headings that describe each article. The searcher attempts to submit keywords or textwords that will result in collecting as many relevant articles as possible, while simultaneously ruling out those that are irrelevant. There is considerable heterogeneity among the database systems and their features,14 even among different versions of Medline.15 Thus, the results of searches can be surprisingly poor. For example, in opthamology, the proportion of relevant articles found in manual searches that were retrieved in Medline was as low as 51%.16 In another study covering 104 questions searched by novices, experienced searchers, and librarians, only 20% of relevant citations retrieved by more than one searcher were found by either of the other two.17 On the other hand, McKibbon et al17 found that the completeness of search results improves with experience over the course of more than 100 searches. Fortunately, ways have been reported to increase the effectiveness of searching techniques. Haynes and Wilczynski18 have provided an excellent list of the best single terms and combinations of terms for various types of evidence in Medline. This is clearly a learned skill, and one can develop better skills.

APPRAISING THE LITERATURE AND APPLYING THE EVIDENCE TO OUR PATIENT Strength of evidence Once a supply of evidence that shows promise of answering the question has been isolated, it will have to be critically appraised as quickly as possible. To determine whether the evidence should influence the provider’s opinion and behavior, or whether it should be discarded, requires some agreement on what constitutes strong and weak evidence. A discussion of the relative strengths and weaknesses of various research designs is beyond the scope of this paper. Control of bias is a major determinant of the strength of a design. The randomized controlled trial (RCT) and the structured critical review or meta-analysis of RCTs are accepted as the “gold standards” of clinical research VOLUME 83 NUMBER 1

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Table VI. The results of a Medline search on â&#x20AC;&#x153;maxillofacial prosthesisâ&#x20AC;? 85-89

90-94

95-98

Type

No.

No. of articles Not classified Not clinical Clinical/laboratory technique Case reports Case series Reviews Controlled unblinded Controlled blinded

122 40 31 19 24 4 3 1 0

100 33 25 16 20 3 2 1 0

137 20 29 13 40 19 15 1 0

100 15 21 9 29 14 11 1 0

49 3 15 6 8 12 3 2 0

100 6 31 12 16 24 6 4 0

design. From a purely methodologic point of view, there is no question that they offer the best assurance of freedom from bias at all stages of investigation. Without randomization and blinding, the estimate of the size of the treatment effect can be greatly exaggerated as evidenced in analyses of multiple, uncontrolled and unblinded studies.19-21 However, it should not be forgotten that many significant clinical innovations have come from basic domains such as materials science. In addition, major new treatment options have been introduced without RCTs. Dental implants are a prime example. Until the advent of osseointegration, the literature was filled with optimistic reports of implant trials based on uncontrolled designs. Ultimately, those implant systems failed and patients were injured along the way. Even the introduction of osseointegration itself was based on large, meticulously followed up, but nonetheless uncontrolled, case series. However, RCTs are expensive to conduct, difficult to blind, often require limited inclusion criteria, or are ethically impossible to undertake. Hence, there are relatively few of them in dentistry, or maxillofacial prosthetics, and where they are available, their generalizability is limited. On issues of treatment, which form the bulk to the maxillofacial prosthetic literature, rigorous study design is needed to avoid bias. In the absence of RCTs, one is left to seek the next best evidence, and rely on it as much as possible given the weaknesses.

the article, so the systems work well in both browsing mode and focused search mode. The Evidence-Based Medicine Working Group at McMaster University provides an excellent example of these appraisal strategy questions in a series of articles in the Journal of the American Medical Association.23-28,41-47 The Therapy Unit asks questions to ascertain the strength of evidence in studies that test treatments (Table V). These questions require a vigorous examination of the methodologic aspects of the article. Only after the reader determines that the methods are valid, does the reader proceed to consider the results. After that is a judgment on the applicability of the results to the patient. This then is a solid basis for deciding whether the article should influence treatment decisions. It is these new skills of literature searching and critical appraisal that are needed for effective EBP. They must also be central to any graduate program in prosthodontics or maxillofacial prosthetics to produce graduates with the ability to maintain their clinical skills after graduation. Without searching and appraisal skills, there is a deterioration in clinical skills, often uncorrected by continuing education. With searching and appraisal skills comes the ability to weed through the useful and useless information efficiently in a focused way, yielding information that will likely have an impact on treatment decisions, and be retained in the mind of the reader.

Appraisal strategy

THE MAXILLOFACIAL PROSTHETIC LITERATURE

There are numerous methods available for doing an assessment of the strength of evidence contained in an article.22-40 They range from a quick scoring system, to an exhaustive analysis of methodology, statistics, and reporting. Most of these systems demand a clearly put question, clear descriptions of the patient populations, methodology and appropriate statistics, and various controls on bias such as random allocation, blinding, and complete follow-up. These strategies usually take the form of questions the reader asks as (s)he peruses

Successfully identifying convincing evidence to support a particular treatment obviously requires that strong evidence be available. One can examine a sample of the maxillofacial prosthetic literature and characterize it against the methodologic hierarchy of research design. The sample in Table VI was taken from Medline on the MeSH heading maxillofacial prosthesis. Titles, abstracts, and MeSH headings were inspected to determine the methods used in the report and the total number of each methodologic type are listed. The arti-

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cles classified as “not clinical” usually presented the results of bench experiments relating to materials, or discussed issues of historical, educational, or economic interest. Another group of articles simply presented a step-by-step “how to” primer on a clinical or laboratory technique. Some reports could not be classified because none of the search fields gave any indication of methodology. In later years, there was a sharp decrease in the number of reports that could not be classified. Clearly, authors and editors are supplying more informative titles and abstracts, now often in structured form, that allow an immediate judgment. Of the remaining clinical articles, which is the primary interest here, the distribution of the articles along the hierarchy of methodologic research design is not impressive because there are so few controlled blinded or even unblinded clinical trials. Although this suggests that the scientific basis for maxillofacial prosthetic treatment is not strong, the available literature should not be disregarded. The exercise, however, does provide a warning that one should be cautious in applying the evidence to patients. It also sends a strong call to strengthen maxillofacial prosthetic clinical evidence, to put the discipline on a solid foundation that will stand the scrutiny of patients, their insurers, the courts, and medical colleagues.

SUMMARY Evidence-based practice is a new level of sophistication in the practice of dentistry. Current clinical skills and judgments are needed as much as ever, and one can still continue to browse the literature looking for the best evidence in support of treatment. However, evidence from dentistry and maxillofacial prosthetics, reveals a diversity of treatment that can be justified only on the basis of weak case series and case report designs. The evidence from medicine suggests that evidencebased practice does affect clinical decisions, and preserves clinical skills. There are ways of obtaining literature efficiently and effectively, and a special set of skills is required to critically appraise it for strength of evidence. Those skills must be developed, and made central to specialty training programs. The weak link in the system at the moment appears to be the methodologic quality of the literature. With more demanding patients, and more discerning readers, editors, and authors will be compelled to provide more rigorous research. REFERENCES 1. Sackett DL, Rosenberg WM, Gray JA, Haynes RB, Richardson WS. Evidence based medicine: what it is and what it isn’t. [editorial] BMJ 1996;312:71-2. 2. Elderton RJ. Variation among dentists in planning treatment. Br Dent J 1983;154:201-6. 3. Grembowski D, Milgrom P, Fiset L. Variation in dentist service rates in a homogeneous patient population. J Public Health Dent 1990;50:235-43.

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Reprint requests to: DR J. D. ANDERSON CRANIOFACIAL PROSTHETIC UNIT TORONTO-SUNNYBROOK REGIONAL CANCER CENTER 2075 BAYVIEW AVE TORONTO, ONTARIO M4N 3M5 CANADA FAX: (416) 480-6801 E-MAIL: jim.anderson@cancercare.on.ca Copyright © 2000 by The Editorial Council of The Journal of Prosthetic Dentistry. 0022-3913/2000/$12.00 + 0. 10/1/102602

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