Format
Introduction How long do restorations last? The ways in which restorations fail:
New disease i)
Caries
ii)
Tooth wear
iii)
Pulpal problems
iv)
Trauma
v)
Periodontal disease
Failure of tooth structure
The failed restorations causes of failure i)
Failure of enamel margin
ii)
Failure of dentin margin
iii)
Bulk loss of tooth structure
iv)
Split root
v)
Loss of vitality
vi)
Resorption
Failure of restorative materials
a) Dental amalgam - Clinical examination of amalgam restorations. - Examination at microstructural level. o Corrosion and tarnish. o Stresses associated with masticatory forces. -
Pain following amalgam restoration.
- Pulp and/or periodontal problem. b) Reasons of failure
- Due to faulty cavity preparation. - Failures due to poor matrix adaptation. - Due to faulty amalgam manipulation. - Microleakage. c) Change of restorative material. d) Techniques for removal, adjustment and repair.
Tooth colored restorations (composite) a) Clinical examination of composite and other tooth colored restorations. b) Reasons of failure – microleakage. c) Guidelines to minimize the chances of failure. d) Change of restorative material.
Glass ionomer a) Change of restorative material. b) Technique for microleakage removal, adjustment and repair.
Failure of cast restorations a) Clinical examination of cast restorations. b) Reasons of failure. c) Repair or removal of restoration.
Failure of pin retained restorations a) Change of restorative material.
Failure of porcelain restorations a) Microleakage b) Change of restorative material.
Total loss of A restoration - Rigid restorations. - Direct plastic restorations.
Acceptable and unacceptable deterioration or failure - The patients perception of the problem.
- The dentists assessment of the effect of technique failure.
Monitoring technique : Recall and reassessment : - Frequency of recall. - The recall assessment.
Summary and discussion
References - Failure of restorations - Dental amalgam - Pin retained restorations - Direct gold restorations - Failure of direct and indirect tooth colored restorations
Direct : o Composite o GIC Indirect : o Porcelain inlay. o Composite inlay - Failure crowns o Metal crown o Porcelain crowns - Failure of cast restorations - Total loss of a restoration o Rigid restoration. o Direct plastic restoration - Summary and discussion - Acceptable and unacceptable deterioration or failure - Monitoring technique recall and reassessment
- References INTRODUCTION How long do restorations last? A number of surveys have been carried out in general dental practice on the longevity of restorations. The most recent data on the age of restorations at the time of replacement indicates the median age to be 10yrs for amalgam, 8yrs for composite, 3 yrs for glass ionomer, and about 18-20yrs cast gold restorations. In the collective experience of the authors, amalgam restorations last from 9mins to 90yrs! The 9 minutes was a patient dismissed with a high restoration who broke it while putting his coat on in the waiting room. The 90yrs was a lady of 98 yrs, who had an occlusal amalgam placed in a lower first molar when she was a child. The longevity of restorations is dependent on a number of factors including: - The caries risk status of the patient. - The age of the patient, when adolescents and adults are compared restorations last longer in adults. This may reflect the susceptibility to caries of younger people. - The type and size of restorations small restorations last longer than larger ones. - The restorative material. - The diagnostic criteria of the dentist. - Whether the dentist is reviewing their own work or that of another dentist. Changing dentists puts a patient at risk of the diagnosis of failed restorations.
The ways in which restorations fail : Failure may be minor, requiring only monitoring or repair, or it may necessitate replacement of the restoration. NEW DISEASE: i)
Caries: Placing a restoration in a tooth doesn’t confer immunity on the tooth, and new disease may occur either around a restoration or on another aspect of the tooth. New decay at the margin of a restoration is called secondary or
recurrent caries the relevant points may be summarized as follows: - Recurrent caries is primary caries at the margin of a filling. - As with primary caries, lesions may be active or arrested. This distinction is important because arrested lesions don’t require treatment, unless there is a problem of appearance. - It occurs in areas of plaque stagnation and for this reason it is most often seen cervically, particularly where a poorly placed restoration precludes adequate plaque removal. - It can be diagnosed visually or on radiographs. A bitewing radiograph is particularly useful to see approximal, cervical lesions but in order to differentiate the filling from the lesion; the restoration must be radio-opaque. - Stain around a filling is not synonymous with recurrent caries provided the margin of the restoration is intact. - Ditching around amalgam restorations is not indicative of recurrent caries these restorations don’t need to be replaced. - Ditching is usually seen occlusally where plaque removal is relatively easy, but recurrent caries occur cervically where plaque can stagnate.
- Large discrepancies between a filling and a tooth may take it difficult for the patient to clean and replacement may be wise to facilitate plaque control. - A composite restoration which has fractured. This invites plaque stagnation and the restoration should be repaired. Now question arises why does recurrent caries so often occur gingivally? Because mechanical tooth-cleaning can miss cervical areas, particularly on an approximal tooth surface where only an interdental cleaning aid (e.g. gloss, interdental brushes) will remove plaque. - Root surfaces are also easy to miss, particularly close to the gingival margin. This means that reinforcement of oral hygiene instructions, especially focusing on the gingival part of restorations, should be an integral part of operative dentistry. - Aspects of good clinical technique are difficult to achieve in cervical areas. These include: - Moisture control because of the proximity of the gingival margin. - Good adaptation of the filling to the tooth with neither a negative nor a positive ledge. - A cavosurface margin without voids and porosities. It is critical to condense amalgam firmly into the corners of the box in an approximal restoration. - Similarly a composite filling must not be left short in this area. ii) Tooth wear: Placing restorations does not prevent tooth wear occurring either around a restoration or on another aspect of the tooth for this reason it is
very important to diagnose the cause of the disease and attempt to institute preventive measures. iii) Pulpal problems: Heavily – restored teeth are liable to pulpal inflammation. The pulp of a carious tooth which was vital at the time of restoration may still undergo necrosis as a result of either the original disease or damage from the operative procedures to restore it. - Toxins from the necrotic pulp result in inflammation of the periapical tissues and radiographic changes. - Thus teeth with necrotic pulps should be root filled to prevent infection. iv) Trauma: Restoration of traumatized teeth will not prevent further trauma, although the use of a soft vinyl mouth guard (gum shield) in those playing contact sports helps to prevent further injury. These can be made on study models, using a vaccum moulding machine and a sheet of soft plastic, or by more sophisticated means, producing a better fit and better occlusion with the opposing teeth. v) Periodontal disease: Operative dentistry may also fail for periodontal reasons. - The tooth had been well restored recently, but periodontal disease and bone loss have now progressed to the stage where the tooth has to be extracted for the patient’s comfort. This emphasizes that each examination of the dentition must include a thorough periodontal examination.
FAILURE OF TOOTH STRUCTURE : i) Failure of the enamel margin : - Wedge – shaped defects along the margins of a restoration caused by failure of the enamel generally arise because of in correct cavity design. - The margin may have been placed too for up the medically facing cuspal incline and, as a result, may be subjected to heavy occlusal load. - There are occasions where the bulk of the restoration is round and it is acceptable to build one section only; however, if remaining enamel is not fully protected, it well fail again. - If the restoration is gold, it may be repaired with gold fail. - Similarly, a minor defect from flaking of the enamel along an amalgam margin may be repairable so long as the load is not heavy. - On the other hand, loss of enamel around a composite resin margin can rarely be repaired because of loss of adhesion; a complete redesign is generally required. Both amalgam and composite resin require bulk in themselves if they are to support the occlusion, and compromise is undesirable. ii) Failure of dentine margin : It is generally the gingival margin of a restoration that is embedded in dentine, detection of a fault and its repair poses problems. - Often the cause is an operator fault, such as failure to adapt or condense the restorative material adequately at the margin.
- Probably the greatest problem is caused by leaving an overhanging margin on a restoration, because it will retain plaque and lead to recurrent caries. - Root surface caries is a problem for the ageing patient following gingival recession, and the best restoration can fail as a result . - The decision on whether to repair the margin or replace the entire restoration depends on two factors. Access to the lesion is not always easy without undesirable destruction of remaining tooth or, alternatively, the main bulk of the restoration may be of low quality. Under these circumstances, the entire restoration should be redesigned. If the restoration is satisfactory and access is simply, the margin may be repaired with a conservative restoration using glass-ionomer in one form or another. iii) Bulk loss of tooth structure : - Loss of an entire cusp is distressing for the patient. - This situation often arises because the dentist has failed to take into account the weakened nature of the remaining tooth structure in an extensively restored tooth and failed to provide some form of protective restoration. - The design of any restoration that involves preparation of a cavity into the dentine on the occlusal surface of a posterior tooth atleast doubles the length of the cusps. Further preparation of the proximal box doubles the length again, leaving the tooth susceptible to splitting. iv) Split root : - This usually occurs in the remaining root structure of a non-vital tooth that has been restored with a post crown.
- A split in a root will allow the development of tensile forces on the cement that will eventually destroy the cement and lead to the loss of the crown. - Diagnosis of a split root is very difficult and almost invariably, terminal to the life of the tooth. - When a post crown becomes uncemented, the remaining root must be carefully explored for signs of a split. - The use of magnification and fibre-optic lighting to illuminate the tooth from various angles may be sufficient. - A caries-detecting dye may help, or simply applying leverage may show percolation of gingival fluid on the root face. After the diagnosis has been confirmed, it must be acknowledged that long-term repair is impossible, and an alternative restoration should be planned. v) Loss of vitality : Modification of the treatment plan will need to be made following loss of vitality, whatever the cause. - There is likely to be a shift in the translucency or color of the remaining crown and some further weakening following the enlargement of the root canal during root canal therapy. The failed restorations : Causes of failure and how to prevent them : IDJ 1990;40;354-358. Failure of restorations is generally due to two causes : - Mechanical. - Biological.
Mechanical failure is often related to the incorrect use of materials or to a lack of understanding by the dentist of stress analysis when preparing teeth for restoration. Biological failure often starts because of microleakage around the restorations leading to secondary caries and destruction of supporting dentin. Pulpal sensitivity occurring after cementation of restorations is often blamed on the materials used, but more often is caused by overpreparation, thermal trauma, leaking provisional restorations or too thin a mix of cement. FAILED AMALGAM RESTORATIONS : Evaluation of all restorations must be done systemically in a clean, dry, well-lighted filed. Clinically evaluation of amalgam restorations requires visual observation, application of tactile sense with the explorer, use of dental gloss, interpretation of radiographs, and knowledge of the probabilities that a given condition is sound or at risk for further breakdown. At least distinct conditions may be encountered when amalgam restorations are evaluated. 1)
Amalgam blues.
2)
Proximal overhangs.
3)
Marginal ditching.
4)
Voids.
5)
Fracture lines.
6)
Lines indicating the interface between abutted restorations.
7)
Improper anatomic contours.
8)
Marginal ridge incompatibility.
9)
Improper proximal contacts.
10)
Recurrent caries.
11)
Improper occlusal contacts. If these conditions are seen clinically then the amalgam
restorations should be replaced to prevent further bad consequences of restoration and tooth. 1) Amalgam blues : Discolored areas or amalgam blues are often seen through the enamel in teeth that have amalgam restorations. - This bluish hue results either from the leaching of corrosion products of amalgam into the dentinal tubules or from the color of underlying amalgam as seen through translucent enamel. The latter occurs when the enamel has no dentin support, such as in undermined cusps, marginal ridges and regions adjacent to proximal margins. - When other aspects of restoration are sound, amalgam blues are not indicative of caries, so restoration is not defective and require no further treatment. - However, replacement of the restoration may be considered for elective improvement of esthetics or for areas under heavy functional stress that may require a cusp capping restoration to prevent possible tooth fracture. - Discoloration can be due to caries also, since the discolored area is so extensive it is likely to indicate caries, which is likely to be residual. If it is recurrent (new caries), a new lesion would be present next to the filling . 2) Proximal overhangs :
Proximal
overhangs are diagnosed visually tactilely, and
radiographically. - The amalgam tooth junction is evaluated by moving the explorer back and forth across it. If the explorer stops at the junction and then moves outwardly on to the amalgam, an overhang is present. - Overhang also can be confirmed by catching or tearing or dental gloss. - Such an overhang can be a plaque trap, provide an obstacle to good oral hygiene, and result in inflammation of the adjacent soft tissue, if causing problems, an overhang should be corrected, and this often indicates replacement of the defective restoration. 3) Marginal gap or ditching : Marginal gap or ditching is the deterioration of the amalgam – tooth interface as a result of wear fracture, or improper tooth preparation . - It can be diagnosed visually or by the explorer dropping into an opening as it crosses the margin. Shallow ditching less than 0.5 mm deep usually is not a reason for restoration replacement, because such a restoration usually looks worse than it really is. - If the ditch is too deep to be cleaned the restoration should be replaced. In addition secondary caries is frequently found around the marginal ggps. Near the gingival wall and thus warrants the replacement. 4) Voids : Voids other than ditching also occur at the margins of amalgam restorations.
- If the void is at least 0.3 mm deep and is located in the gingival third of the tooth crown, then the restoration is judged as defective and should be repaired or replaced. - Accessible small voids in other marginal areas where the enamel is thicker may be corrected by recon touring or repairing with a small restoration. 5) Fracture lines : - A careful clinical examination will dental any fracture live across the occlusal portion of an amalgam restoration. - A line that occurs in the isthmus region generally indicates fractured amalgam and thus a defective restoration that needs replacing. - However, care must be taken to evaluate correctly and such line, especially if it is in the midocclusal area because this may be an interface line, a manifestation of two abutted restorations, each accomplished at a separate appointment. - If other aspects of the abutted restorations are satisfactory, replacement in not necessary. 6. Improper anatomic contours - Amalgam restorations should duplicated the normal anatomic contours of the teeth. Restorations that impinge on the soft tissue, have inadequate embrasure form or proximal contact, or prevent the use of dental floss should be classified as defective, indicating recontouring or replacement. 7. Marginal ridge incompatibility
The marginal ridge portion of the amalgam restoration should be compatible with the adjacent marginal ridge. - Both ridges should be at app. The same level and display correct occlusal embrasure form for passage of food to the facial and lingual surfaces and for proper proximal contact area. - If the marginal ridges are not compatible and are associated with poor tissue health, food impaction, or the inability of the patient to floss, the restoration is defective and should be recontoured or replaced. 8. Improper proximal contacts: The proximal contact area of an amalgam restoration should touch a closed contact the adjacent tooth at the proper contact level and with correct embrasure form - If the proximal contact of any restoration is suspected to be inadequate, it should be evaluated with dental floss and/or visually by trial angulations of a mouth mirror to reflect light and actually see if there is a space at the contact open contact. For this viewing contact must be free of saliva. - If the contact is open and is associated with poor interproximal tissue health and/or food impaction, the restoration should be classified as defective and replaced. 9. Recurrent caries : Recurrent caries at the marginal area of the restoration is detected visually, tactilely, or radio graphically and is an indication for repair or replacement.
FAILURES IN AN AMALGAM RESTORATION : I. Failures due to faulty cavity preparation II. Failures due to poor matrix adaptation III. Failures due to faulty amalgam manipulation. IV. Microlekage.
I.
FAULTY CAVITY PREPARATION : Improper cavity preparation leading to recurrence of caries and
fracture is the greatest single factor responsible for failure. Healey and philips (1949) evaluated 1521 defective amalgam restorations and reported that 56% of the failures were because of improper cavity preparation and 42% of the failures were because of faulty manipulation of amalgam. The different causes of failure that can occur at various steps while preparing a cavity for amalgam are as follows: a)
Inadequate occlusal extension: Inadequate extension to include pits and fissures increases the
chance of caries recurrence particularly in oral cavities with high dental caries index. On the occlusal surface the preparation should be extended to include all the susceptible pits and fissures while terminating the margins in areas that can be finished. b)
Inadequate extension of the proximal box : If the proximal box walls are not adequately extended into the
embrasures they are not amenable to brushing and cleaning by mastication, which predisposes to secondary caries. Special attention should be directed towards lower bicuspids and the distal regions of the
maxillary and mandibular first molars where frail walls can be formed easily. c)
Overextension of the cavity preparation walls :
• The ideal facio-lingual width of the cavity preparation for amalgam should be 1/4th the intercuspal distance. • If the cavity preparation extends to half of the intercuspal distance, consideration should be given to capping of the cusps. • If the remaining cusps are not capped in large amalgam restorations, there are chances that cusps can fracture. This is because amalgam restoration acts as a wedge and tends to split the opposing cusps apart. d)
Amalgam cavity preparations should have a minimum depth of 1.5 mm to provide it bulk and hence resistance to fracture.
e)
If the pulpal floor of the cavity preparation is not flat but curved the restoration produces a wedging effect thus increasing the chances of the fracture of tooth.
f)
To assure strong junctions between amalgam and tooth regardless of its location, but joints should be created particularly in those regions where occlusal stresses are to be encountered.
• If the cavosurface angle is acute there are chances of fracture of the tooth margins where as if the cavosurface angle is obtuse the acute marginal amalgam is likely to collapse under occlusal stress. • The cavity margins should be adequately finished to remove any unsupported enamel rods, which are susceptible to fracture leading to gap formation and subsequently secondary caries. g)
Failure to round off the axio-pulpal line angle as well as internal line angles and point angles can lead to concentration of stresses and fracture of the tooth or restorative material. The
rounding off the axio-pulpal line angle also provide bulk of the silver which is required for its strength. h)
Occasionally, fracture may be seen at the isthmus portion of the proximo – occlusal restoration, which may be because of a very narrow isthmus relative to the rest of the cavity preparation or inadequate proximal retention form.
i)
Failure to diverge the mesial and distal walls of the occlusal cavity preparation. When the mesiodistal extension of the cavity is extensive it can cause fracture because of the undermining of the mesial and distal marginal ridge enamel.
j)
Retentive devices should be prepared entirely in dentin without undermining the enamel.
k)
Incomplete removal of carious tooth structure leads to failure of amalgam restoration.
l)
Flat pulpal floor should be provided around the excavation site of caries.
m)
Post operative pain can also be a routine failure. The dentist should use high speed rotary instruments, with intermittent cutting and adequate cooling of tooth structure there by minimizing the post operative pain.
II.
POOR MATRIX ADAPTATION : • The areas and relationship of contacts, the anatomical designs of the marginal ridges, the marginal continuity of the restoration all play important roles in assuring that the tissues of the periodontium will maintain a state of health. • The proper contacts and contours in a restoration can be obtained by a properly contoured and applied matrix. The matrix should be very stable after it has been applied.
• Instability of a matrix results in a distorted restoration, gross marginal excesses and an uncondensed soft amalgam. • The cervical excesses can irritate the periodontium, gradually and progressively destroying the periodontium. • A complete and effective condensation cannot be attempted against a poorly stabilized matrix, which will result in and a soft amalgam filled with voids. Hence establishing a proper contacts and contours with the help of matrices are fundamental to the successful amalgam.
III.
FAULTY AMALGAM MANIPULATION : It has been state that more amalgam restorations fail because of
poor manipulation than because of the use of poor alloys. The basic principle of all these manipulative procedures is to produce a well – prepared amalgam with the mercury content in the amalgam under control. a) •
Mercury alloy ratio : A serious loss of strength occurs when the residual mercury is in excess of 55% in the restoration.
•
The clinical result of excess residual Hg includes reduced crushing strength, increased flow, increased susceptibility to tarnish and corrosion.
•
It is preferable to use a minimal Hg technique with dispensers used for the correct proportioning.
Mulling is a continuation of the trituration process and is done to assure that all alloy particles are duly coated with Hg. It can be done manually or mechanically. While doing manually, moisture can be incorporated into the material if bare hands are used. Mechanically mulling is done in amalgamator. The pestle is removed from the capsule and trituration repeated for 1-2 seconds. This procedure helps in mulling and cleaning the capsule of amalgam remnants. Amalgam, which hardens in the capsule if not removed will contaminate future mixes and is frequently a cause of hard amalgam islands that pull out of the plastic mass while the filling is being carved. Hence the capsules should be checked carefully for cleanliness after each use. Both under trituration and over trituration can lead to failures of amalgam restoration. Under trituration leads to soft powdery noncoherent mix where as over-trituration may break the already forming matrix. b)
Condensation : The rationale of condensation is to reduce residual mercury
content, to ensure amalgam reach all parts of the preparation and to obtain a homogenous restoration devoid of voids. • Freshly prepared amalgam has more desirable working properties. • The effectiveness of removing residual Hg from the restoration is possible only if the amalgam is used with in 4 mints of trituration. Delayed use of triturated amalgam does not allow proper condensation of the material and also does not remove the Hg from the restoration.
• Replasticizing the mix by adding Hg will seriously reduce its strength. • Condensation can be carried but either manually or mechanically, condensation should be done using the stepping process to drive away any voids from the restoration. Such increments should be used rather than larger increments to ensure proper condensation. • Very small plugger sizes may punch holes in the amalgam where as very larger plugger size may not condense the amalgam in all corners. Condensation pressure used should be adequate. • The packing motion is most effective if the condenser is rocked under a heavy steady thrust. Light tapping on the other hand will remove very little Hg to the surface. • The mechanical condenser, however, should be used with caution to avoid fracture of enamel margins. c) •
Contamination : Contamination of the amalgam mix during trituration, mulling and condensation, by moisture weaken amalgam restoration especially with Zn containing alloy.
•
There occurs delayed expansion, which could possibly result in marginal flaws, tarnish, pitting, corrosion and blistering etc,
• d) •
Expansion may also lead to pain. Finishing and polishing : The amalgam should be finished gently. Occasionally during finishing excess amalgam at the margins is dressed down to thin flakes or spur like overhangs, which can fracture from the restoration sooner or later, thus leaving susceptible crevices in vulnearable areas of the tooth surface.
•
Over carving the restoration to create normal, deep anatomic features should be avoided. An over carved restoration well reduce the thickness of the amalgam and increase chances of fracture.
•
Amalgams that have a greater tendency for tarnish and corrosion don’t retain surface polish for a long time. They may also offer resistance to polishing. A rough promoting plaque accumulation and gingival irritation.
•
For polishing if temperature generated is above 650 C Hg is released from the amalgam leading to defective restorations.
e)
Post-operative pain :
This may occur following an amalgam restoration because of : •
Hyper
occlusion
leads
to
inflammation
of
due
apical
periodontium. •
Cracks in tooth such cracks cause pain during chewing because of expansion / contraction of the tooth structure will every bite.
•
Galvanism not only the adjacent / antagonist dissimilar metal restorations lead to galvanism, but in poorly condensed silver amalgam, variation in silver concentration at different areas of the same restoration, also different areas of the same restoration, also leads to galvanism.
•
Delayed expansion is peculiar with zinc containing alloys.
•
Failure in the form of pain may occur if inadequate pulp protection is present. Amalgam is a good conductor of heat. If a base is not given, heat may be conducted to the pulp resulting in its damage.
•
Varnish should be routinely applied under amalgam restorations. Failure to apply proper varnish layer can lead to continuous
leakage around the restoration. This leakage may cause postoperative sensitively and amalgam blues due to penetration of corrosion products in dentinal tubules. •
The restoration fracture may occur if the patient does not follow the instructions properly and bites on restoration before it sets.
IV.
MICROLEAKAGE :
• Amalgam when freshly condensed does not adapt closely to the walls of the prepared cavity. Generally, a gap of 10-15 µm width exists around the restoration. • Amalgam has a unique property that is; the adaptation of the restoration to the cavity wall improves with time, hence referred to as a ‘self sealing restoration’. This is by virtue of the formation and accumulation of corrosion products in the interface with the passage of time. The corrosion products are the oxides and chlorides of tin mostly occurring in the lower copper alloys. However, high copper alloys confer a greater resistance to corrosion. Because of this increased resistance and a slower rate of forming corrosion products, microleakage in the high copper restorations continue for a longer period of time. • Microleakage occurring as a result of dimensional changes in amalgam is quite minimal. During setting of the conventional Hg / alloy mix, a small contraction is seen initially when the Hg is consumed. This is followed by a small expansion as the crystalline matrix is formed. • According to ADA specification number 1, a dimensional change of 20 µm/cm is allowable for a set amalgam.
• The coefficient of thermal expansion of amalgam (25x10-6/0 C) is also not very much different from that of the tooth structure (11.4x10-6/0 C). • Hence the change in dimensions of the gap because of thermal changes is moderate for amalgam. Prevention of microleakage : 1)
Different types of silver alloys exhibit different levels of microleakage : •
According to (Saiku et al, 1993 ; Mahler, 1996) spherical alloys display more microleakage and post operative sensitivity compared to lathe cut or admixed alloys. This is because of the difficulty in obtaining a close adaptation with spherical alloys and or more shrinkage of spherical amalgam as it sets. Lateral condensation helps to overcome this problem to a great extent for spherical amalgams.
2)
Condensation of amalgam should be carried out immediately after trituration : • A longer time lapse results in the loss of plasticity and increase the chances of internal voids and layering. • Thorough condensation with adequate pressure removes voids and promotes adaptation of the material to the cavity walls. A pressure of 10 pounds is considered optimal when using a 2 mm condenser point, however the amount of force required varies with the shape of the alloy particle. • Condensation should be first begin in the center and the condenser point gradually worked towards the periphery using the stepping process. Thus removes any air space and pushers the material
against the cavity walls, there by decreasing the incidence of microleakage. • According to (Chapman and Crim, 1992) mechanical means of condensation has shown to be superior to hand condensation in controlling marginal leakage. 3)
Burnishing
of
amalgam
after
condensation can reduce microleakage by aiding adaptation of the material at the margin and enhancing homogeneity : • The effect of burnishing on the degree of marginal leakage varies with the particle shape of amalgam. • With spherical alloys, no reduction of leakage results from the burnishing procedure compared to lathe cut and admixed alloys, probably because the spherical shape of the alloy allows the particles to be ‘pushed aside’ during the process. 4)
Alloys with lesser creep values show a smaller degree of marginal leakage. A creep rate of less than 3% is considered acceptable under the ADA specification No. 1. • Low copper alloys show a creep value ranging from 0.8 – 8.0% compared to high copper alloys which have much lower values of 0.1 – 1%.
5)
Sealing the cavity walls with a varnish under an amalgam restoration prevents microleakage at least until the corrosion products of amalgam begin to fill the microspace : • However the benefits offered by a varnish don’t exist as long the life of the restoration. Because of the solubility in the oral environment, its effectiveness is limited to app six months and by
the end of one year almost all the benefits are lost. This time lapse is sufficient for the corrosion products to replace the varnish and permanently seal the inter face. • Application of a varnish layer under high copper amalgams didn’t prove to be effective in reducing any microleakage. 6)
Sealed amalgam restorations : • In these types of restorations, a coating of unfilled resin is placed over the restoration margins and the adjacent enamel after having etched the enamel surface. • Although the resin may finally wear away, it delays microleakage until the corrosion products are accumulated in the interface.
7)
Use of gallium alloys : Gallium alloys as an alternative to amalgam alloys were introduced
long ago but didn’t gain much popularity. These are alloys of GalliumTin – Indium (liquid) and a silver based alloy similar in composition to the high copper amalgam alloy (powder). Many of its physical and mechanical properties and handling characteristics are similar to silver amalgam. One major advantage with the use of these alloys is that because of the very high wetting ability, the final restoration is highly resistant to microleakage. They have such a high wetting characteristics that when the gallium rich mixture is inserted into the cavity, some of it tends to move up along the sides of he instrument. CHANGE OF RESTORATIVE MATERIAL : Selection of the material for restoration of the initial lesion and then for each replacement should take into account such factors as :
• Caries rate • Occlusal load • Ability to protect remaining tooth structure • Economic considerations. Indications : • Relatively simple, inexpensive to use and reasonably tolerant of careless placement technique. • Physical properties are generally adequate to withstand occlusal load. • Efficient and cost effective for the restoration of average to medium - sized cavities because carving and contouring direct in the oral cavity is straight forward in the presence of guidance from remaining tooth anatomy. • Can be used to a degree to protect remaining tooth structure. • Excellent in the presence of a high caries rate because it corrodes and seals it own margins and is economical to repair.
Contraindications : • Contains Hg, a known health hazard to dental staff. • Poor aesthetics ; tends to produce a blue-gray color change in any tooth. • Of limited use in the restoration of extensive cavities because of the difficulty of restoring correct occlusal anatomy directly in the mouth. TECHNIQUES FOR REMOVAL, ADJUSTMENT, AND REPAIR : • Amalgam is a relatively easy restorative material to remove. • An appropriate size and shape and Beaver bur is used in the air turbine, and is inserted into the middle of the restoration and moved towards the cavity walls. • Small fragments of amalgam may be left attached to the cavity walls and over the pulp ; these are then broken away from the wall or floor with an excavator or probe. Removing amalgam in this was avoids unnecessary over-cutting of the cavity. No attempt should be made to freshen-up the margins. • The cavity walls will often be discolored by corrosion products from the amalgam filling. Both the enamel and dentin may be discolored and this tissue should not be removed unless it is soft. Soft dentin may represent residual caries that a previous dentist left in place. This is usually hard and dry. • It may be remove with an excavator although it is minimally infected and this is not essential. • Recurrent caries presents as primary caries around the filling margin and soft infected dentine should be removed.
• Thus the cavity should only be extended where caries dictates, where it has proved to be unretentive, or where the margin requires modification for other reasons such as chipped enamel or incorrect cavosurface angle. • Old lining material need not be removed unless caries has spread underneath it or the patient has symptoms of pulpitis and the operator wishes to look for an exposure. However a decision to repair rather than replace a restoration should always is reviewed during the repair. • Where new disease on another aspect of the tooth necessitates extension of a restoration, consideration should always be given to retaining part of the original filling. • Exactly the same argument applies to restorations where part of the tooth fractures away. The original restoration may well be retained and a new cavity designed alongside and with in it.. • However, there is awed for some mechanical retention (such as a lock) between the new and old filing and / or a bonded amalgam. This technique can be particularly useful where pins are present in the original restoration. It is very difficult to remove such a restoration leaving the pins intact. • If the pins are cut off when the restoration is removed, new pin sites will have to by found and this is difficult and risky for the pulp and periodontal ligament. The possibility of replacing failed amalgam restorations with composite or glass ionomer – composite layered restorations should be considered.
For example, they should be considered for the replacement of the restorations shown in. • Composite could also be used for the premolar particularly if the cause of the amalgam fracture was that the cavity was too shallow. In this instance a composite could be placed without deepening the cavity, where as this would be necessary for a replacement amalgam. AVOIDANCE OF FAULTS IN AMALGAM RESTORATIONS : IDJ 1990-;40:354-388 To avoid faults the following guidelines should be followed : 1)
Where ever possible use microcavity preparations.
2)
Finish all cavities to a butt joint, preferably at 90 0 to the cavo-surface.
3)
Don’t create sharp internal line angles. Rounded external cervical line angles reduce stress.
4)
Avoid shallow isthmuses and wide approximal embrasures. Increase the depth of the restoration to improve load bearing capacity.
5)
Use high – copper alloys to minimize corrosion.
6)
Avoid contamination of the alloy with saliva during packing.
7)
Wedge matrix bands firmly to maintain the contact area.
8)
Line the dentine with a GIC to prevent corrosion products entering the tubules.
9)
Where a high incidence of secondary caries is experienced, use a silver-cermet lining carried 2 mm up the proximal box as a cariostatic seal.
10)
Adhesion of amalgam alloys to glass ionomer bases may be improved by priming the surface of the cement with 25%
polyacrylic acid solution. Protection of the dentine with GIC and surface conditioning prior to packing the amalgam alloy is preferable to the use of varnishes. 11)
Capsulated amalgam alloys ensure greater consistency of alloy / Hg ratios.
FAILURES OF PIN RETAINED RESTORATION : Failures after pin placement and / or restoration may occur in five area : 1)
In the dentin i.e., fracture of tooth : The solution is to reduce the area to a flat surface and re-drill a
pinhole. 2)
At the dentin / pin interface i.e., pin pulls out along with the restoration : •
The treatment includes re-cementing if it a cast pin restoration, or performing the whole procedure again if it is an amalgam restoration. It is generally difficult to determine the size of the pin that will suit the pinhole. Quite often, the patient brings along with him the lost restoration and in such cases the size of the pin can be measured with a micrometer and the next larger size chosen.
•
If no pin is available for measurements, the operator should chose by using successive sizes of pin starting with the smallest size possible.
3)
In the pin itself i.e., pin fractures :
Remove any remaining restorative material from the cavity preparation. Fractured pins are managed similar to as described earlier and the restoration done again. 4)
At the pin / restoration interface i.e., restoration pulls away from the pins:
• Formation of corrosion products at the interface is the most common cause for such type of failures. Titanium is the least corrosive pin. • The treatment includes removal of any remaining restorative material. Pins are checked for loosening. There is every possible chance of having loosened pins during restoration removal. • Loose pins are managed as described earlier and the restoration done again.
5)
Failure of the restorative material itself i.e., restoration fractures : The most common cause fro such type of failures is an improperly
retained matrix. • Any movement of the matrix during placement, condensation and setting of amalgam can severely weaken the restoration and result in a poorly adapted interface with the pin. • The occlusion should be checked thoroughly as any high point predisposes to restoration fracture. Treatment : • The treatment includes repair of the restoration, if possible. • When restoration cannot be repaired, the remaining restorative material is removed and the tooth restored again. • Any pins loosened during restoration removal should be adequately managed.
FAILURE OF GOLD RESTORATION: Occasionally, gold will fail along a margin as a result of further wear on the occlusal surface, particularly if opposed by a ceramic restoration with a high wear factor, and caries may progress very rapidly. • Repair of the margin with gold foil may be adequate. • If the occlusal load is not great, glass – ionomer cement can be utilized in a very conservative repair. CHANGE OF RESTORATIVE MATERIAL : Indications : 1)
When well constructed, gold restorations show the greatest longevity and this will often justify their use.
2)
Physical properties are ideal for the restoration of the occlusion.
3)
Indirect methods of construction are generally utilized and this allows for the ideal reconstruction of all aspects of anatomy, both occlusal and proximal.
4)
Can be used in very thin section for protection of remaining tooth structure.
Contraindications : 1)
Gold restorations are complex to construct, with the potential for error at any one of a number of stages, and are therefore relatively expensive.
2)
Gold cannot be recommended in the presence of a high caries rate.
3)
Aesthetics is a matter of opinion and some patients regard this as unsatisfactory.
4)
Gold itself has no built in resistance to bacterial invasion. However, glass – ionomer luting cement will release fluoride and may provide some protection.
Microleakage around direct gold restorations : Direct gold restorative materials adapt to the cavity walls most efficiency. When properly placed, they serve better than other materials and prevent recurrence of decay. The decreased marginal leakage can be attributed to the good adaptability of gold to the preparation walls because of inherent qualities as : • High malleability and ductility of gold provides burnishing which contributes to reducing leakage by riding the gold over the marginal voids. • A short bevel on the cavosurfaces margins facilitate the burnishing, contouring and polishing there by promoting close adaptation at the cavity restoration interface. • Complete insolubility in the oral fluids. • The method of condensation induces elastic compression of the underlying and surrounding dentin, which adapts the material strongly after completion of the condensation. If gold is improperly compacted into the cavity, air spaces / voids may be left behind at the gold tooth interface enhancing microleakage. • Voids at the margins are particularly common when a convex surface in the center is formed during the building of a gold restoration.
• Other reasons for the existence of voids in the restoration can be attributed to the type of gold selected, non-uniform method of stepping, improper lines of force and inadequate condensation pressure.
Measures to reduce leakage in gold restoration : 1)
In general, mat and powdered gold are porous and hence less effective than regular cohesive gold foils in obtaining a good cavity seal. It is therefore recommended that the former should be used for forming the internal bulk of the restoration of the gold foil and the latter be used as a veneer on the surface to prevent leakage.
2)
Uniform stepping of the condenser point in individual steps as well as lines of steps by half or one fourth is indicated to drive away all air spaces and closely adapt the material to the under-lying surface. Stepping should always proceed from the center to the periphery.
3)
Lines of force should be directed at 90 0 to the pulpal floor in the center of the cavity preparation and then changed to 450 to the cavity walls at the periphery.
4)
Average force of 10 pounds applied with a 1 mm condenser point is considered optimal for proper adaptation of the material to the cavity walls and cohesion of two gold surfaces.
5)
Building of the restoration should be done in a convex form i.e., material should always be banked on the cavity walls a head of the center. This allows application of forces in a right direction and thorough adaptation.
6)
Surfaces procedures like burnishing, finishing and polishing bring the metal closer to the tooth structure improving the marginal seal.
FAILURES OF DIRECT AND INDIRECT TOOTH COLORED RESTORATIONS : Clinical examination of composite and other tooth colored restorations : • Evaluation of all restorations must be done systematically in a clean, dry, well – lighted field. • If there is in improper contour or proximal contact, an overhanging proximal margin, recurrent caries, or other condition that impairs cleaning, the restoration is considered defective. • Corrective procedures include recontouring, polishing, repairing, or replacing. • One of the main concerns with anterior teeth is esthetics. It a tooth colored restoration has dark marginal staining or is discolored to the extent that it is esthetically displeasing and the patient is unhappy with the appearance, the restoration should be judged defective.
• Marginal staining that is judged non carious may be corrected by a small repair restoration along the margin. Occasionally the staining is superficial and can be removed by resurfacing. Failures in composite restoration : Composite restorations are very technique sensitive, therefore utmost care is necessary before, during and after their manipulation. • Even one percent compromise during any step can lead to failure of the restoration. The visible modes of failures seen in composite restoration are : i)Discoloration, especially at the margins. ii) Marginal fracture iii) Recurrent caries iv) Post-operative sensitivity v) Gross fracture of restoration vi) Lack of maintaing contact vii) Accumulations of plaque around the restorations. The failures can be avoided and atleast minimized, if meticulous approach is followed during cavity preparation and manipulation of composites. The following features usually lead to failure in composites : a)
Incomplete excavation of caries: During cavity preparation, the caries is not thoroughly removed.
• The left over caries hinders with the bonding mechanism. •
Similarly if ZOE is not removed thoroughly form the base of the cavity and the walls, thus will also lead to failure.
b) Incomplete etching or failure to remove residual acid from the enamel tags
- Proper concentration of acid along with proper etching time is mandatory to achieve the requisite tags. - Flourosed renewal require more etching time, however the total etching time should not be more than 60 seconds. - Repeated touch after etching, blowing with compressed air under pressure and/or sweeping the etched surface with cotton can lead to fracture of these tips leading to lack of proper union between the enamel tags and resin. - Many a times, the acid is not washed out thoroughly and the residual acid in the tags hinders with the bonding, subsequently failure of the restoration. - The gel etchant should be washed for 20-30 seconds and the liquid etchant washed for 10-15seconds. - For drying, air from chip syringe should be used. - Three way syringe should be avoided as the air could be contaminated by machine oils or water which condenses in the pipelines. c) Double or nonuniform coat of bonding agent:. - Bonding agent is to be applied gently and uniformly all around the cavity walls. - Double coat of bonding leads to marginal leakage and also, nonuniform bonding at certain areas hinders the union of material with the bonding agent. d) Lack of isolation: - Isolation is a very important step in composite restoration. A rubber dam application is mandatory, otherwise cotton rolls should be kept ready and change the same even during the manipulation.
- Gingival retraction cords can be utilized wherever changes of tricking of gingival fluid is there especially in class III and class V cavities and also in composite laminates. - Patients with uncontrolled salivation, drugs can be used. e) Touch of composite with fingers: - The composite in any case should not be touched with fingers. - Many a times, the operator uses his finger to pack or keep the material in place. This practice is to be avoided. - Always pick and hold the composite with Teflon coated instruments. Sometimes the composite falls over the tongue and the operator picks it up and pack the same into the cavity. This will lead to failure. f) Avoid bulk placement of composites: - The composite is to be placed in increment and each increment should be as small as possible, since the contraction after polymerizataion leads to gaps at the tooth restoration interface. - These gaps consequently lead to post-operative sensitivity, marginal leakage and secondary caries. g) The curing of the composite should be from all the sides. The filter and the bulb vis-a vis the intensity of the light should be checked off and on to ensure the proper curing. For proximal restoration, fine curing tips can be used. - The light reflecting wedges can be used, however care should be taken while curing the gingival area. h) Composites should be finished and polished thoroughly especially at the beveled areas. The occlusion should be checked before final polishing. Antagonist tooth, if impinging can be grinded off. i) Microleakage around composite restorations
Composite resins on their own don’t possess the capability of bonding to either enamel or dentin. The inability to bond coupled with marked polymerization shrinkage and thermal expansion/contraction predispose to marginal leakage. - Microleakage at the enamel restoration interface can be eliminated almost completely if sufficient enamel thickness is present. - Conversely, the bond to dentin though substantially reduces microleakage but does not protect the dentin restoration interface completely. - The tight adhesion to dentin is limited by a number of factors like vitality of the dentin, difference in physical and chemical composition of dentin compared to enamel, presence of dentinal fluid, smear layer and etc. - Development of internal stresses from polymerization shrinkage and thermal effects also has a detrimental effect on the bond. - Microleakage therefore continues to be a problem in almost all composite restorations. The most notable factors that contribute to marginal leakage of composites are: 1. Composite resin restorations are very much tech sensitive. Any step that goes beyond the actual procedure will lead to failure including an increase in marginal leakage. 2. Marginal gaps formed at the tooth restoration interface primarily result from dimensional changes like polymerization shrinkage of the setting resin. After the resin has set, the size by masticatory forces, thermal changes and peater sorption. 3. All the composite restorative resins shrink during polymerization. The volumetric polymerization shrinkage usually is in the range of 1.67-5.68%, the lesser being for the light activated ones.
- In case of a bonding agents being used to bind the restorative resin to the tooth structure, shrinkage results in the development of tensile and/or shear stresses at the tooth restoration interface. With in certain limits, the adhesive bond is able to withstand these stresses. Once the stresses exceed the bond strength and the plastic or elastic deformation of the combined system, as separation at the tooth restoration interface may occur leading to microleakage. It is usually the bond with the dentin which is compromised during shrinkage where as the bond with enamel is sufficiently strong to with stands the same amount of forces. 4. Functional stress incurred on restorations by cyclic mastication is another factor in inducing microleakage of resin restorations. Occlusal stresses enhance leakage because of repeated plastic or elastic deformation of the restoration. 5. The marked difference in the coefficient of thermal expansion of restorative resins and tooth structure also has a detrimental effect on adhesion. - The composites have a coefficient of thermal expansion ranging from 22-55x10-6/0C comparatively higher than the tooth. Combined thermal and occlusal stresses have shown to induce more micro leakage as compared to leakage induced by individual stresses. 6. Composite resin restorations have a tendency to absorb water from the environment, causing the restoration to expand. Thus the property of water sorption is able to counteract polymerization shrinkage to a little extent. - In contrast to the polymerization contraction stresses, which are generated at a rapid rate, relief of stresses by hygroscopic expansion proceeds more slowly.
- The resins with the largest quantity of filler have the least water sorption (water uptake is the property of the resin component of the matrix). - It should be stressed here that though water sorption may improve marginal adaptation of composite resin, it impairs its mechanical properties. 7. Incidence of marginal gaps are higher on the cervical margins of a class II restoration, the reasons being: a) placing the restorative material at these areas is difficult. b) Entrapment of air during placement. c) Difficulty during condensation because of the pull back of sticky material. d) Inadequate bonding to the gingival wall due to polymerization shrinkage.
Measures to reduce marginal leakage A number of techniques have been advocated to enhance marginal adaptation and reduce micro leakage of composite restorations. These include: 1. Choice of composite material Micro filled composite resins provide a better marginal adaptation over the macro filled composite resins. This can be attributed to two reasons. a) greater flexibility of the micro fills during polymerization shrinkage decreases the contraction forces that tend to threaten the forming dentinal bond.
b) These show a larger absorption of H20 resulting in an expansion which counteracts some of the polymerization shrinkage. These facts indicate the use of microfilled resins in all situations where strength is not a major requirement. 2. Cavity design Design should be as conservative as possible to overcome the disadvantages of polymerization shrinkage and wear under occlusal stresses. - Moreover, composites are adhesive to the underlying tooth structure thereby limiting the need for retentive and extensive preparations. - Modified cavity designs, placement of bevels, reduced depths and rounded internal angles are very effective in providing good marginal adaptation and reducing leakage. - Not only the size but the shape of the cavity is also an important factor in determining the width of the marginal gap.
Adhesive Gap width (um) (-) Absent 13 7 4 (+) present 3 1 0 Width of the marginal gap in relation to the shape of the dentin cavity. This shows three dentin cavities of identical diameter but of different shapes. ď ą
The cavity to the right is V shaped and the cavity to the left is box shaped.
When the cavities are filled with composite resin without any intermediate bonding agent, the marginal gap is seen to reduce from 13mm to 4mm from left to right.
Where as when an intervening dentin bonding system is applied, the gap width is in the order of 3mms to almost nil. This can be explained on the decreasing ratio of volume/bonded are from 1.0 for the box shaped cavity to 0.4 for the V-shaped cavity. (Hansen and Asmussen, 1985)
The role of bevels on the cavosurface margins in reducing leakage remained controversial. The principle behind giving bevels is to increase the surface area for enamel bonding and reduce micro leakage. • Occlusal beveling is usually not required because of the enamel rod direction and the possibility of extending the material to load bearing areas. • Placement of bevels is recommended mainly on the accessible facial and lingual margins of the proximal box. • Microleakage was limited to enamel of facial and palatal margins in 75% of the beveled restorations compared to 30% of not beveled surfaces. • Beveling gingival margin of class V preparations is not advocated as it usually increases micro leakage. (owens et al, 1998). 3. Acid etching tech and bonding Acid etching removes surface contaminants, raises the surface energy and reactivity of enamel and increases the surface area for bonding. Subsequently, the bonding agent is drawn by capillary attraction into the micro porosities created by acid etching.
These polymer tags provide micro mechanical interlocking with enamel there by reducing micro leakage to almost nil. The short coming with this tech is its dependence on the presence of thick enamel at the cavity walls. The effectiveness of marginal seal is compromised by the position and surface structure of enamel as it anatomically varies in different areas of the same tooth. The results are obvious when the restoration margins are located in the cervical enamel. Cervical enamel is thin, irregular in prism structure and devoid of characteristic prism markings. Therefore the bond to cervical enamel is not very intimate compared to the more occlusally placed enamel. This is reflected in the microleakage scores, which are almost negligible on the occlusal cavosurface margins but are significant on the gingival margins. Acid etching on dentin was traditionally discouraged because etchants were thought to open and widen the dentinal tubules resulting in increased permeability and bacterial ingress to the underlying pulp. However, with the introduction of the newer and better hydrophilic resins over the earlier hydrophobic ones, the concept has now changed. Many authors now propose deliberate etching of dentin to create open tubules and a porous Intratubular layer. It is believed that a close adhesion can then be attained between the resin adhesive and treated dentin preventing the penetration of toxic materials leading to pulpal irritation. It has been reported that the leakage was not uniform along the interface. While some areas may show no microleakage, others may leak entirely from the cavosurface margins to the pulp.
The non uniformity of bonding may be attributed to various factors like differences in the thickness of smear layer, different degrees off etching, wetness, force of polymerization contraction etc. which may vary on the same surface. Another type of leakage that is recently receiving a lot of special attention is the ‘nanoleakage’, described by Sano et al (1995) This leakage occurs with in the nano spaces around the collagen fibrils with in the hybrid layer that have not been completely infiltrated by resin. It has been shown to occur both at the bottom of the hybrid layer and/or scattered along its entire width, depending upon the bonding system employed. It appears that bonding systems that etch deeper into dentin are likely to show higher degrees of nanoleakage. This could be the possible reason for reduced degree of leakage observed with self etching/self priming system than with systems that use an acidic conditioner as a separate step. Poorly infiltered hybrid layer contains voids that predispose to accumulation of water and oral fluids which may accelerate the degradation of the bond. When demineralized dentin is fully infilterated with resin, its modulus of elasticity is much higher than the values of the original demineralized dentin. If the hybrid layer fails to be penetrated completely, its modulus of elasticity wight falls in between that of adhesive resin and the uninfiltered dentin collagen. Contact with water and oral fluids would provide a gradual decrease in the modulus of elasticity of the bonded interface reducing the stress concentration in this area and hence preserving its integrity for short period, but due to slow hydrolysis the
long term effect is jeopardized. Therefore, dentin bonding agents though are an effective measure in reducing microleakage, their long term performance under stress and continued exposure to oral fluids is still questionable. Recently, new bonding agents based on glass ionomer technology have been developed e.g. scotch bond multipurpose and Pertae universal bond. These have carboxylic acid groups incorporated inside them that become available for attachment to dentin. They are also useful in attaching composite resins to glass ionomer cement surfaces. These agents can be separately grouped as ‘glass ionomer bonding agents’. Another newly advocated material is the diluted version of the resin modified GIC such as fuji bond II LC. Which can be used to completely replace the conventional bonding agents under a composite resin. These would be advantageous in reducing leakage because of high chemical adhesion and coefficient of thermal expansion close to that of tooth St. 5) Cavity filling technique : Volumetric contraction of thick layers or bulk material in a cavity can induce significant shrinkage of the entire mass and subsequently the high stress generated may debond some adhesive systems leading to microleakage. Placing composite resin in small multiple increments to fill the cavity is therefore recommended to control polymerization shrinkage and the contraction gap at the margins. Applying the material in layers assumes importance especially in class II and class V cavities where the resin does not adequately bond to the gingival margins.
The amount of polymerization shrinkage can be markedly controlled if the resin to filler ratio is decreased. This phenomenon led to the introduction on the concept of beta quartz glass inserts used as mega fillers in composite restorations. Inserts are made of lithium aluminosilicate glass containing modifiers to give it a natural tooth appearance, and are available in various sizes and shapes. The choice of the insert is controlled by the cavity dimensions. Shrinkage in a composite restoration is a function of the resin matrix. Inserts tends to inc the filler consent relative to the amount of resin, decreasing this contraction. They also have a low coefficient of thermal expansion of 4x10-6/OC and exhibit no polymerization on shrinkage and H2O sorption. Prepolymerized composite ball, have also been substituted for the glass insert. Applequist and Meiers (1996) compared the microleakage potential of both the inserts. Prepolymerized composite ball containing restorations showed significantly greater microleakage, probably because of the high cumulative internal stresses generated during thermal changes. Beta quartz insert has a coefficient of thermal expansion close to that of dentin, which is therefore expected to reduce additional stresses on the interface. Recently, the method of ‘soft start polymerization, has been advocated to reduce marginal gap and improve marginal integrity. The procedure involves a short prepolymerization at low intensity followed by the final cure at high intensity. This allows composite resin to flow during the initial setting period thereby minimizing the stresses induced at the interface.
Prolonging the curing time of a composite resin improves upon the microleakage by allowing a greater inversion rate of the monomer component. 6) Direction of the light source : It is presumed that the polymerization shrinkage vectors of setting composite resin are direction towards the light source. This has a practical importance especially when curing proximal restorations. Because of the inadequate access of the light guide in proximal areas and also since the curing tip is usually directed from the occlusal aspect, the gingival increment shrinks occlusally. Use of curing aids like light directing wedges, flexible light guides and focusing tips can facilitate better curing in areas of poor access and invert the shrinkage vectors of composite resin towards the gingival floor in proximal areas. A three sited light curing technique for better adaptation of conventional class II composite restorations was suggested by Jutz et al (1986). 7) Sealing the marginal gaps : An unfilled low viscosity resin is applied to the margins by slowly brushing the resin laterally from one side to another after the composite restoration has been finished and polished. In a ten year clinical study by Mertz Fair hurts et al (1998), sealed composite restorations placed over frank cavitated lesions were successful in arresting the clinical progress of the carious lesions. Materials used for the purpose of sealing gaps are the commercially available pit and fissure sealants. 8) Delaying the finishing process : Finishing techniques and their timings have shown to affect the ability of restorative materials to resist leakage.
Most authors advocate finishing of composites to be delayed for 24 hrs, until the polymerization is complete. If done before the initial setting, it seems to break the bond between the resin and the tooth. In a study conducted by Fusayama and Kohno (1989), finishing after 3 mints of insertion resulted in a considerable microleakage at the enamel and dentinal cemental margins, more so in the latter. Finishing after 5 mints and 1 day after insertion was considered acceptable as it resulted in almost no microleakage. Yap et al (1998) have however suggested that finishing of composite restorations
should
be
carried
out
immediately
after
light
polymerization. According to them, delayed finishing after 1 week doesn’t improve but instead can be detrimental to the already formed marginal seal of the restorations. Stresses which may disrupt the adhesive bonds are almost always generated during the finishing of restorations. Variations in the finishing techniques have also shown the affect leakage. Increased leakage occurs with the use of dry finishing techniques, suggesting a detrimental effect of high heat on the marginal adaptation. It is therefore recommended that rotary instruments while finishing and polishing be run at slow speeds using light intermittent strokes and with generous air coolants. Use of soflex disks for contouring and finishing have shown to provide the best marginal quality for composite restorations. 9) Use of cavity liners and bases : Calcium hydroxide and glass ionomer cements are the most commonly used base materials in a composite restoration.
The two reasons advocated for their use in deep cavity preparations are. a) They serve as protective agents for pulp and. b) Their presence reduces the bulk of composite resin the cavity and subsequently the polymerization shrinkage. Criticism is however leveled for these restorations because it is believed that the polymerization shrinkage of composite resin breaks the seal of glass ionomer cement to dentin. Hotta and Aona. The contraction tends to pull away the 1994 base away from the cavity floor resulting in a gap not less than 5µm at the cavity restoration interface. Any gap created has a potential for leakage and fluid percolation. In shallow cavities the loss of seal is often related to the strength and thickness of the base used, and thin linings of less than 1mm are considered unsatisfactory. Light cure glass ionomer when used as bases shows a slightly better performance compared to their chemically cure counterparts. Though gaps are also created with the former, yet their sizes are smaller. This is probably because of their ability to adhere immediately to the dentin and achieve high early tensile and compressive strengths. The hardened cement resists stresses that tend to disrupt the dentinal seal in a better way. 10) Use of composite inlay restorations : Composite inlay restorations bond to the tooth structure using composite as a cementing medium. The resins employed may be either chemically cure or dual cure. Light cure composite luting agents are usually not advocated as it is difficult to cure them through a preprocessed resin restoration which exceeds 2mm in thickness.
Composite inlay seems to be very efficient way of managing polymerization shrinkage since the bulk of the contraction occurs prior to cementation. Ziskind et al (1998) have shown definitely less leakage with inlay systems compared to direct resin restorations, but no significant difference in leakage between the direct and indirect methods of inlay fabrication. Since the luting cements are less heavily filled than the actual resin restorative materials, they tend to lose earlier by the wear mechanisms. The hybrid luting resins are more susceptible to wear than microfilled ones. Hence microfilled resins should be preferred for the cemerntation purposes. Another drawback in their use is that the cement often fails to bond chemically with the inlay. This is attributed to the curing procedure which induces a very high conversion rate of the inlay and greatly reduces the availability of remaining unconverted monomers for copolymerization with the resin lute. A passage for microleakage is hence created resulting in marginal staining. Studies have demonstrated failure of composite to cement bond by almost 60% after 6 months. For improving the bond between processed composite restorations and the resin cements, different methods have been advocated like: a) Use of a solvent such as ethyl acetate to soften the cavity side of the restoration prior to cementation. b) Sand blasting the cavity surface of the restoration with aluminium oxide abrasive particles so as to increase the surface area for bonding.
c) Etching the cavity side of the composite restoration with 10% hydrofluoric acid. 11) Expanding matrix resins for dental composites : Composite resins that expand slightly during polymerization may be the future of restorative resins. These would facilitate bulk placement of the material, reduce postoperative sensitivity, secondary caries and microleakage.
GLASS-IONOMER CEMENT : Failure of restorative material : I should not be placed under heavy occlusal load, it is usually not subject to marginal or bulk failure. If such problem should occur, complete replacement is probably the best solution. Microleakage: I cement adheres to the tooth structure by forming chemical bond between carboxyl groups of the cement and calcium ions of the tooth. In addition to this important property of chemical adhesion which contributes to decreasing microleakage, other properties are: a) A coefficient of thermal expansion which closely matches that of tooth structure. b) Fluoride releases into the surrounding environment. c) The ability to renew broken ionic bonds. All these features help to have long term cavity sealing properties. GI cement is highly technique sensitive and the most critical aspect is isolation from moisture for the first 30 minutes after placement.
On exposure to water the matrix forming ions are easily leached out during the initial set which could interfere at tooth restoration interface. Solubility in oral fluids continues to be a problem for 24 hrs following insertion of the material. Excessive dehydration / dessication can result in a chalky, crazed or a cracked surface which if extends to the margins could result in considerable marginal leakage. Coating the restoration with surface protective agents like cavity varnishes or unfilled resins is highly recommended for protecting against dehydration. Once the cement has attained full maturity, it becomes highly resistant to solubility and disintegration in the oral fluids. Another factor that harms the marginal integrity of the restoration is the use of the sharp hand instruments for finishing before the material has completely set. Measures to reduce microleakage (preventing failures) : 1)
Proper manipulation and placement of GIC on dentinal surfaces
only
after
they
have
been
adequately
cleaned.
Formulations of lower powder: liquid ratio than recommended increase the solubility of the cement. 2)
Use of rotary instruments over manual cutting instruments is advocated in finishing restoration margins. The latter have shown to tear away the material at the margins resulting in marginal ditching.
3)
During finishing restoration surfaces should always be coated with Vaseline or petroleum jelly to protect from moisture contamination and dessication.
4)
Prior (conditioning) of the tooth surface before insertion of GIC increases the bonding and possibly reduces microleakage scores. Various agents advocated for the purpose are tannic acid, poly acrylic acid, citric acid etc.
RMGIC, because of rapid initial setting, reduces the effect of moisture contamination. Unfortunately, RMGI have occasionally shown increased levels of microleakage compared to the chemically cured ones. This is probably because of the resin component in the former that causes it to shrink during polymerization and setting. In contrast to the slow setting chemically cure glass ionomer cements which permit stress relief, the resin modified systems exhibit more rapid setting contraction through light polymerization. Moreover, less water and less carboxylic acid content also decreases the wetting ability of light cure glass ionomer cements to the tooth substance promoting marginal leakage. To a certain extent, expansion due to H 2O uptake which is a function of the resin component of the cement compensates for the initial resin shrinkage and reduces microleakage. 5)
Where laminated composite / glass-ionomer restorations are required, use at least a 0.5 mm thickness of cement. Don’t acid etch until the cement is sock hard to the touch. Fast setting lining cements generally reach this level after 4 mints.
6)
In case where very thin linings of GI are required in the laminate
or
‘sandwich’
tech,
the
light-cured,
GIC
are
recommended. 7)
Sliver – cermet cements will provide better resistance to abrasion than the regular glass-ionomers.
Technique for removal, adjustment and repair composite and glass ionomer cement :
Tooth-coloured filling materials are much more difficult to remove than amalgam because the colour of the composite or GIC is almost impossible to distinguish from the tooth when under the water spray. Use of an air turbine is again obligatory and small tungsten carbide or diamond burs may be chosen. The technique is similar to that with amalgam except for the following : The materials should never be chipped away from the enamel or dentine walls because these materials are adhesive and the forces are likely to fracture the enamel at the cavity margins. The operator should stop frequently and the dental nurse should dry the tooth. A colour difference between tooth and composite will now be easier to see. Repair of these materials is an accepted technique as the new filling bonds to the old with adequate strength in some clinical situations such repairs can be particularly well executed by the use of airbrasion to remove the surface and defective areas of the old restorations. The rough surface is excellent for giving a mechanically rough surface for bonding where new material is to be added to old, it is important to cut some of the old material away to produce a clean surface for bonding. Where a restoration is subject to occlusal stress it is usually better to replace it.
FAILURE OF INDIRECT TOOTH COLORED RESTORATIVE MATERIAL (PORCELAIN) : Dental porcelain is a brittle material with low tensile strength and fractures easily if the strain exceeds 0.1%, therefore it requires adequate bonding to the underlying tooth surface for gaining structural and functional integrity. Earlier, ceramic inlays/onlays/crowns were bonded to the tooth St. using conventional luting cements like zinc phosphate, poly carboxylate, silicate, silicophosphate etc. only to be met with high rates of failure. With the growing advancements in adhesive technology resin systems have now almost completely replaced the earlier luting cements for bonding and supporting the restoration to the cavity surface. The resin cements employed should preferably be dual cure to allow polymerization to be completed in areas inaccessible to light. An adequate bond of the ceramic inlay and the resin luting agent is attained by treating the surface of the former both mechanically and chemically. First, acid etching of the inlay surface is done using HF acid for fired porcelain and ammonium bifluoride for Milled and cast ceramics. This provides a surface for micromechanical retention of the luting resin. The etched surface is the n silanated to promote witting with the resin there by improving chemical retention. However the chemical bond
between silane and luting composite improves only the initial bond strength later on, this bond is weakened severely probably by hydrolysis, which lead to marked decrease in bond strength after one year. Resin luting cement should not be applied without prior tooth bonding procedures because significant microleakage could occur due to inherent polymerization shrinkage. Microleakage has been considerably reduced with the use of resin luting agents over conventional cements but not elminated. The most vulnerable site continues to be the wear of cement lute itself and its interface zones with the inlay and the tooth. Interfacial gap widths have shown to vary amongst the different systems used for fabrication of inlay probably because of the technique sensitivity. In general, it is difficult to prepare ceramic inlays that will precisely fit the cavity preparation. For the fired ceramic restorations the fit is highly dependent upon the patience and skills of the dental technician. Glass ceramic restorations (Dicor) have shown excellent marginal behaviour invitro with virtually no marginal openings. Naturally, closer the fit of the restoration to the preparation surface better will be the resistance to marginal leakage. Conflicting results continue to exist regarding the microleakage performance of ceramic and resin inlay systems. The interfacial marginal gaps so formed after the loss of cementing medium have shown to be both wider and deeper for the ceramic inlays compared to the composite inlays. Another possible route for microleakage is between the ceramic and composite material, which could lead to marginal staining. This insufficiency in bond could be either because of the carelessness on
part of the operator or gradual degradation on contact with H 2O/oral fluids. Porcelain crowns : (IDJ 1990, 40, 354-358) Failure of porcelain crowns is due either to fracture in service, or cementation failure. Porcelain crowns are highly resistant to corrosion and colour changes will occur only when porous surfaces attract stain. Failure of cementation is due primarily to poor fit or lack of retention. The ideal crown preparation should be a miniature replica of the tooth, and small teeth with a lack of coronal height are less retentive and a frequent cause of bridge failure. Ideally preparations should not diverge on the axial walls by more than 100. Detailed analysis of the stresses placed on restorations have been given by McLean. In particular, aluminous porcelain jacket crowns, castable glassceramic crowns and slip-cast alumina ceramic crowns are more prone to failure on undercut, short, or over tapered preparations. The pure ceramic restoration fractures through deepening of microcracks on the fit surface and should not be used where occlusal stress is high. Bruxists, deep incisal overjets and group function occlusions are but a few examples of unfavourable occlusions. By contrast the metal ceramic restoration is capable of much better resistance to occlusal stress. The metal coping not only reinforces the porcelain and reduces tensile failure but, more significantly, protects the inner surface of the porcelain from mechanical failure due to deepening of microcracks.
Protection of porcelain surfaces from crack propagation due to stress corrosion effects is now being recognized to be of equal importance as the type or thickness of metal used. Even the metal – ceramic restoration may fracture where continuous occlusal stress occurs, such as in a group function occlusion. Gold occlusal surfaces are necessary in those cases, and even where canine disclusion reduces stress on the posterior teeth the lingual surface of the canine is better constructed in metal to reduce wear of the opposing natural tooth. The use of all-ceramic bridgework is another area fraught with difficulty. Even where connector areas are heavily reinforced, it should be appreciated that the effects of static fatigue are much greater in ceramics than metal. T/T plan : Meticulous treatment planning is required prior to placing porcelain veneers or inlays. Whenever possible, porcelain veneers should be bounded to enamel onlay. Gingival margins should not be finished in root dentine where the long-term hydrolytic stability of the resin cement is in doubt. Where dentine is exposed, it should be lined with GIC. In areas where onlay this linings can be used, a light-cured, glassionomer is preferable. Where incisal dentine is exposed and there is no enamel support, porcelain veneers will be placed under greater stress. The dentine-resin-porcelain veneer may be likened by a constant strain system in which the material with the highest modulus (porcelain) will bear a greater proportion of the occlusal load.
Ceramic inlays and onlays : Ceramic onlays can be made of feldspathic ceramic materials in a traditional way by sintering or, as a more recent technique, by milling. Glass ceramic inlays can be cast or pressed using the lost wax technique or they can be produced by milling. CAD/CAM technique is implemented in the Cerac system, which mills ceramic inlays from industrial blocks of ceramic material that are prefabricated under optimum and controlled conditions. Annual failure rates of ceramic inlay restorations range from 0% to 7.5%. Annual failure rates of CAD/CAM ceramic restorations range from 0% to 4.4%. Bulk fracture is a frequent cause of failure of ceramic inlays, secondary caries, deterioration of marginal quality over time. The risk of fracture of a ceramic inlay depends, among other factors, on the strength of the material. Ceramic materials the brittle and susceptible to failure in tensile mode, while their resistance to compression is high. Flaws at internal or external surfaces are in many cases the origin of cracks, which can propagate and lead to catastrophic failure. Other factors, such as the design of the cavity preparation, the shape of the restoration (mini thickness; 1.5mm) and internal fit influence the strength of the ceramic restoration. Wear of the resin cement in the luting gap results in marginal deterioration of ceramic restorations, especially in the first year after restoration placement. Composite inlays and onlays : Annual failure rates of posterior composite inlays and onlays range from 0% to 11.8%.
Many of the problems associated with the direct placement of large posterior composite restorations can be overcome with the use of an indirect composite inlay technique. It has been concluded that composite inlays are a good, longer-lasting alternative to direct plastic composite restorations in large class II situations. Indications for esthetic inlays include teeth in which strengthening of the remaining St. is indicated, the cavity is free from marked undercuts, and the patients are regular attenders requesting toothcolored restorations in posterior teeth. The indirect technique allows the production of restorations in the laboratory with appropriate proximal contours and contacts and control of anatomic from. Post curing the inlay with heat, pressure, and or light increases the degree of conversion through an annealing process, improving the mechanical properties of the composite and resulting in better wear resistance. Failure in composite inlay and onlay occurs due to secondary caries, fracture and post operative sensitivity, marginal opening.
CAST GOLD INLAY AND ONLAY : Annual failure rates of cast gold restorations range from 0% to 5.9%. Compared to other restorations for posterior teeth, cast gold restorations are considered to be costly but long lasting. Tooth fracture, marginal defects, insufficient retention, and secondary caries are the main reasons for the failure of cast gold inlays. If the size of a lesion requires the replacement of one or more cusps, gold inlays or partial crowns are still an excellent method to achieve
tooth restoration, despite the possibility offered by adhesively bonded all ceramic restorations. Microleakage around cast restorations : Generally the cast restorations don’t offer close adaptation to the cavity walls. A gap ranging from 10 to 160 µms has been reported in various cast restorations. An intermediate layer of dental luting cement is therefore necessary to seal the interface and aid in retention. But this layer might sometimes promote leakage. Though the recent cements are less soluble in oral fluids, (the ZuPO 4 cement earlier used with cast gold restorations was highly soluble, yet none of the materials totally resist the solubility in oral fluids. In case of gold, the placing of bevels and burnishing the margins to reduce exposure of this cement line. The interfacial space is closed primarily by elongating and/or compressing the cast gold because of the ductility and malleability. Permanent deformation of the gold alloy occurs which results in a physically closing the discrepancy at the margins. Marginal gaps which exceed 0.1mm should not be burnished, rather the castings remade. Restorations that have a close fit (with in 20µms) to the adequately designed preparation surfaces resist degradation of the cement lute and increase life of the restorations for longer periods. Another cause of promoting leakage in cast restorations is the excessive taper of the underlying preparation. Under the continuous application of loads, the restoration gives away by rotating on the preparations surfaces. This results in a break in the
cement lute and fracturing of the thin metal margins leading to leakage and even dislodgement.
SUMMARY : ACCEPTABLE AND UNACCEPTABLE DETERIORATION OR FAILURE : Wide variation occurs between dentists in deciding which restorations have failed and should be replaced. The patient’s perception of the problem. The patient’s opinion can and should influence the dentists advice. The patient shown in this fig was unhappy with the appearance of the composite restoration, therefore this restoration, which was otherwise acceptable, was replaced. Some patients would be prepared to accept this appearance. Sometimes dentist and patient don’t reach agreement because the dentist cannot accept that the patients request is in their best interest when this happens, they should agree to differ and part company. On no account should a dentist be persuaded to carry out treatment which they believe to be ill-advised. A patient’s request to replace all their amalgam restorations with tooth-coloured fillings is a good example of this. The dentist may consider that research evidence indicates that large restorations would not serve as well if composite was used instead of amalgam. The dentist’s assessment of the effect of technical failure.
The patient is often unaware of technical failure. The fractured restorations and the restoration were causing no symptoms but both were replaced because of the danger of development of recurrent caries. - An occlusal amalgam with one small part fractured away. The cavity is very shallow (probably the cause of the fracture), easy to clean, and symptomless. Such a restoration might be left since its replacement with amalgam would result in the destruction of further sound tooth substance. However, a sealant restoration could be considered. The ditched restorations also should not be replaced automatically. Ditched restorations should be accepted and put under review. This approach is particularly applicable in mouths which are not cariesprone. However, where a margin is severely ditched, so that it will admit the tip of a periodontal probe, plaque accumulation and therefore caries is encouraged. In this case it may be logical to repair only that part of the restoration, concentrating on improving it. If the amalgam is used for the repair, a small retentive cavity is prepared. Alternatively, a composite can be used, in which case the ditched crevice is prepared as for a composite restoration. Unfortunately, it is common to see ledges on amalgam restorations on bitewing radiographs. These ledges usually cause plaque accumulation and gingival inflammation. Bleeding on gentle probing with a pocket measuring probe is evidence of this inflammation. Usually the ledge should be removed or the restoration replaced to aid plaque control. MONITORING TECHNIQUES : RECALL AND REASSESSMENT
Monitoring dental health or restored health is one of the most important aspects of dental care. A course of treatment involving operative dentistry does not end once restorations have been completed. The aim of the initial course of treatment is to determine the level of dental disease, to find the cause, to arrest it by preventive means, and to provide restorations as required. It is the patient’s efforts to improve plaque control, to control diet, and to apply other preventive measures which are of prime importance. It is patients who primarily control caries, not dentists. Patients vary both in their susceptibility to the disease and in the lengths to which they are prepared to go to prevent it. However, preventive advice may be more readily accepted if it is regularly reinforced. Thus dentists recall their patients to repeat and modify any relevant preventive advice, to detect any new disease sufficiently early for preventive measures to arrest it, and to detect and repair technical failure. Frequency of recall : How frequently should patients be seen for reassessment? There is no general rule that can be applied to all. High caries risk patients should be reviewed at three-monthly intervals. Medium-risk patients should return for review after one year and longer periods may be appropriate for low-risk patients. The patients age and the natural history of the disease should also be considered. Frequent recall to check oral-hygiene is appropriate with some children, with fissure sealants being placed if good oral hygiene is not established.
As for as tooth wear is concerned, a six-month or annual recall is usually appropriate where wear is excessive for the patient’s age. The recall assessment : It is important to recheck the medical history carefully, but questions about past dental history need not be asked again except to check that no other dental treatment has been provided in the interim. The vitality of heavily-restored teeth should be checked, paying particular attention to those where direct or indirect pulp caps were placed at the last visit. Study casts are of particular assistance in monitoring the rate of tooth wear. It is easier to compare two sets of casts than original casts with the current clinical picture. The recall visit is in many ways one of the particular pleasures of the profession. When dentist and patient first meet they know very little about each other, but as the years pass they because better acquainted. Both dentist and patient often come to expect what will happen at the recall visit, perhaps a check that all is well and catching up on a year’s news of family and work events. However, there is a trap here for unwary professional. It is all too easy to assume that the mouth is stable or to perform a perfunctory examination, perhaps missing signs of early root caries, bleeding on probing in some areas, a sinus discharging over a nonvital tooth, or even an early malignancy, attention to detail is vital. If, as a result of proper history, examination, and special tests, treatment is required, the dentist should differentiate between that caused by essentially preventable disease and that occasioned by mechanical, aesthetic, or functional defects. The former require the patient’s active cooperative in further prevention action.
REFERENCES: 1) Sturdevant’s Art and Science of Operative Dentistry.. 4th edition. 2) Preservation and restoration of tooth structure. Graham J Mount. 3) Pickard’s Manual of Operative Dentistry 8th edition. Kidd, Smith, Walson. 4) Textbook of operative dentistry. Vimal K Sikri. 5) The failed restoration: causes of failure and how to prevent them. IDJ, 1990, 40: 354-358. 6) Longevity of restorations in posterior teeth and reasons for failure. J Adhesive Dent, 2001, 3: 45-64. 7) Unserviceable crowns and fixed partial dentures: life span and causes for loss of serviceability. JADA, 1970, 81.
8) A survey of crown and fixed partial denture failure: length of service and reasons for replacement. JPD, 1986, 56 (4)