Chapter 17 - Partial dentures – the story continues

Chapter 17 Partial dentures – the story continues

Teeth may be lost by virtue of neglect, accident or via treatment planning; they may also be missing for congenital or acquired reasons. People with missing teeth may opt to have them restored, or not, largely because of sociological, functional or, in the case of non-restoration, for financial reasons.

How teeth are replaced largely depends on the level of (dental and technological) sophistication on offer. In eighteenth-century England, ivorine teeth ‘adorned’ the mouths of gentlemen but were removed at mealtimes; equally, there are records of Etruscan noblemen wearing bridges to replace lost teeth, the bridges being ‘fixed’ or ligatured in place by wires to the abutment teeth. At the turn of the twentieth century and for the next 50 years, dental technology developed as did options for replacement of lost or missing teeth. In the 1950s and 1960s, as dentistry and dental technology developed, so the list of treatment options increased.

Fixed prostheses became more predictable and more desirable. Where fixed replacement was contra-indicated, removable prostheses became more elaborate, with precision attachments being used to enhance stability and appearance by potentially eliminating clasps. This was truly the pinnacle of the mechanical age of prosthodontics.

In the late 1960s, the research work of Bowen and his team developed the use of adhesive techniques. The use of composite resins and glass-ionomer cements meant that silicophosphate cements became a thing of the past and that the minimally destructive (to tooth structure) techniques associated with adhesive dentistry resulted in potentially superior clinical outcomes allied to potentially superior aesthetic results.

If the next two decades were the beginning of the adhesive era in prosthodontics, then the decade from 1985 to 1995 must be seen as the beginning of the age of biological prosthodontics, in particular the dawn of the age of dental implantology based on evidence-based practice rather than clinical anecdote. As a result of sound clinical trials, the dentist’s quiver of treatment options has now been added to by the arrow of an implant option supporting either a fixed or removable prosthesis.

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The RPD option The option discussed in this article is that of the Removable Partial Denture (RPD) and it is perhaps appropriate that we consider the role of the RPD in the clinical climate of today. A rational overview might question the traditional classifications of RPDs which are either descriptive of the geography of the arches or the nature of support (Table 1).

In practical clinical terms, however, one might consider there to be three separate roles of RPDs, based on how they are to be used and/ or for how long they are used.

These are listed in Table 2.

Recent evidence confirms that the loss of teeth in partially dentate people affects their confidence in social mixing. However, it would appear that outcomes of treatment with RPDs are less well perceived by patients than those who receive fixed prostheses, when Oral Health-Related Quality of Life measurements are made.

The most recent Adult Dental Health Survey highlighted the effects of dental health education on levels of edentulousness in the UK population; in 1968, almost 40% of the adult population was edentulous; currently it is less than 8% and is predicted to fall in the future. In previous surveys, it was reported that the cut-off point for a ‘natural’ functioning occlusion was 20 or more teeth and this was an effective cut-off point for the wearing of RPDs. In addition to direct factors (namely comfort and psychological well-being) affecting patient choice of whether to wear a RPD or not, there are other indirect factors which must inevitably have an influence. These include the influences of the media and also normative influences. For example, clinicians were asked how they would restore missing posterior teeth, given set clinical circumstances relating to patients (e.g. case histories, radiographs and models). Where the scenarios comprised 20 healthy anterior teeth (10 in each arch), in healthy mouths, it was found that, in a fictitious patient aged 35 years, 31.5% of the clinicians would opt for treatment by fixed means and 3.9% by a cantilevered bridge. Similarly, it was found that, for a 65 year old patient and given treatment options of nothing, RPD, bridge or implants, dentists listed their preferences as: When the scenario was for a patient aged 65, the results were:

1) No restoration (63%)

2) Co-Cr - based RPD (25.2%)

3) Implant-supported prosthesis (7.1%)

4) Cantilevered bridge (3.9%)

5) Acrylic resin – based RPD 131

Compared to that for a 35 year old:

1) No restoration (49.6%)

2) Co-Cr - based denture (29.1%)

3) Implant-supported prosthesis (20.5%)

4) Cantilevered bridge (3.9%)

5) Acrylic resin - based RPD (2.4%).

One of the more favoured options listed above is no treatment. In cases of bilateral free-end saddles the philosophy of the shortened dental arch comes into play.

Essentially this works on the principle that middle-aged persons with 20 healthy units (i.e. 5-5 in each arch) are perceived to be able to masticate efficiently.

However, when patients were asked to view models of options for replacement of molar teeth, they listed their preferences as follows:

1) Cantilevered bridge

2) Cantilevered Resin-Retained Bridge

3) Implant-supported prosthesis

4) Acrylic resin-based RPD

5) Cobalt-chromium-based RPD

6) No treatment.

It is thus obvious that there will, for many years to come, be a need to select the treatment option of a RPD, for the reasons outlined in Table 2. To this must be added the fact that current undergraduate dental students are exposed to less clinical (prosthodontic) teaching than previously.

There will be a greater need, therefore, if patients are to receive appropriate treatment at an appropriate standard, for prosthodontic training to continue post qualification. This therefore underpins the importance that dental practitioners follow an accepted rationale of planning RPDs. The following is one such guideline: 1) Outline and classification of saddles The clinician should assess the position of saddles and also determine the clinical and patient related factors of the saddles, e.g. location, size, oral health, manual dexterity, perceived motivational aspects.

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2) Determination of the restoration of the saddles

Factors to consider here are:

• Conditions of all tissues adjacent to and in the saddles

• Conditions of remainder of mouth

• Inter-arch assessment, i.e. 3-D assessment

• Masticatory needs • Maintenance.

3) Determination of the nature of the support for the prosthesis

Philosophically, prostheses may be supported in one of six ways;

• Tooth supported. These prostheses may be fixed, removable or fixed and

removable.

• Implant supported. These may also be fixed, removable or fixed and

removable.

• Tooth and implant supported. These may also be fixed, removable or fixed

and removable.

• Tooth and mucosal borne. These may be fixed (e.g. Spring cantilever bridge)

or removable.

• Implant and mucosal borne. These tend to be removable.

• Mucosal. These are clearly removable.

4) Determination of the means of retention for the prosthesis

Retention is derived in a variety of ways;

• In the case of removable prostheses, retention is achieved principally from

direct retainers. Direct retainers may be :

i. Clasps: occlusally-approaching or gingivally-approaching

ii. Precision attachments: intra-coronal; extra-coronal; studs; bars and others

(e.g. Ipso-Clip) iii.

Guide Planes

iv. Planned use of soft-tissue undercuts.

Clinicians will also be aware of the occasional beneficial effects of denture fixatives on unretentive dentures. N.B. The clinician is required to use a surveyor to identify and quantify undercuts and to plan paths of insertion etc.

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5) Determination of how the saddles will be connected

In fixed prostheses, the connecting elements are called pontics. These may be

sanitary pontics or ‘conventional’ ridge-lapped pontics.

In removable prostheses, there are six forms of connector to consider in the

maxilla and five in the mandible. Anatomical and functional aspects should be

considered here, in addition to patient-related factors.

Maxillary connectors. The six varieties here are:

• Full palatal coverage

• Palatal bars (anterior or posterior)

• Skeletal design (anterior and posterior bars)

• Palatal strap • Horseshoe • Labial bar.

Mandibular connectors. The five varieties here are:

• Lingual bar

• Lingual bar and continuous clasp (Kennedy bar)

• Sub-lingual bar • Lingual plate • Labial bar.

6) Identification of anti-rotational elements

These elements ought to be considered in free-end saddle cases or Kennedy 1

cases where the prostheses are tooth and mucosa or implant and mucosal-

borne.

Indirect retainers are supporting elements which resist rotation on the other side

of the axis of rotation (e.g. clasp tip) from the saddle (Figure 2).

7) Determination of how components are joined

The clinician, in conjunction with the technician, has to plan the position and

form of e.g. minor connectors or, in fixed prostheses, if post-ceramic soldering is

required.

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8) Re-appraisal for health and maintenance

Here, the ability of the patient to achieve and maintain acceptable degrees

of oral cleanliness and health must be re-assessed as well as a determination of

how the prosthesis/es may be maintained.

Legends to Figures Figure.1.

This unilateral bounded saddle has been restored with a denture retained by two intra-coronal attachments Figure.2.

The shortened dental arch of the mandible (opposing a maxillary complete denture) has been extended by CRRBs bilaterally Table 1. Traditional Classifications of RPDs.

Table 2. Roles of RPDs based on usage.

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