Partial dentures in a dentate world by Fraser McCord, Professor of Prosthetic Dentistry, Manchester Dental School
Figure 1. This unilateral bounded saddle has been restored with a denture retained by two intra-coronal attachments. 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 - financial reasons. How teeth are replaced largely depends on the level of (dental and technological) sophistication on offer. In 18th-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 20th 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 contraindicated, removable prostheses became more elaborate, with precision attachments being used to enhance stability and appearance by potentially eliminating clasps (Figure 1). 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 techniques1. The use of composite resins and glassionomer 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.
Figure 2. The posterior edentulous saddles have been restored by implant-supported fixed prostheses. If the next two decades were the beginning of the adhesive era in prosthodontics, then the decade 1985-95 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 (Figure 2).
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.
Table 1. Traditional classifications of RPDs.
Recent evidence confirms that the loss of teeth in partially dentate people affects their confidence in social mixing2. 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 made3. This is reflected by changes in trends of referral to outreach clinics in restorative dentistry between 1991 and 2001, with complete denture referrals rising from 12 per cent of cases in 1991 to 19 per cent of cases in 2001. Whereas 6 per cent of referrals in 2001 were for RPDs, requests for treatment of missing teeth (presumably by non-RPD means) rose threefold to 12 per cent (p=0.046). The recent Adult Dental Health Survey4 highlights the effects of dental health education on levels of edentulousness in the UK population; in 1968, almost 40 per cent of the adult population was edentulous; currently it is less than 19 per cent and is predicted to fall in the future. In the same survey, 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 wellbeing) 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, a recent survey by Nassani5 sought to determine how clinicians 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 per cent of the clinicians would opt for treatment by fixed means and 3.9 per cent 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. 2. 3. 4. 5.
No restoration (63 per cent); Co-Cr-based RPD (25.2 per cent); Implant-supported prosthesis (7.1 per cent); Cantilevered bridge (3.9 per cent); Acrylic resin-based RPD.
Compared to that for a 35-year- old: 1. 2. 3. 4. 5.
No restoration (49.6 per cent); Co-Cr-based denture (29.1 per cent); Implant-supported prosthesis (20.5 per cent); Cantilevered bridge (3.9 per cent); Acrylic resin-based RPD (2.4 per cent).
Table 2. Roles of RPDs based on usage.
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. This philosophy was promulgated by Kayser6. 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. This finding, coupled to the fact that 30-50 per cent of denture wearers never or only occasionally wore their dentures7, should lead dentists to consider the cost-effectiveness of this form of treatment in bilateral free-end saddles. If the acceptable survival rate of cantilever resin-bonded bridges (CRBBs) in a hospital-based observational study8 is considered in apposition to the proven cost-effectiveness of CRBBs that were demonstrated to be similar to the conventional option without the invasiveness of the latter, then perhaps this option should be considered as a valid one in appropriate mouths of good oral hygiene. In a randomised controlled study Jepson et al.9 demonstrated that CRBBs may be as efficacious a means of restoring the shortened dental arch as RPDs (Figure 3). This was perceived to be especially valid by patients who found the CRRBs to more comfortable than RPDs. One could also imagine that as laboratory costs of CRRBs and RPDs are similar and that the 'biological cost' of the former was likely to be less than the latter to the patients.
Figure 3. The shortened dental arch of the mandible (opposing a maxillary complete denture) has been extended by CRRBs bilaterally. In the study reported by Nasanni5, however, when patients were asked to view models of options for replacement of molar teeth, they listed their preferences as follows: 1. 2. 3. 4. 5. 6.
Cantilevered bridge; Cantilevered Resin-Retained Bridge; Implant-supported prosthesis; Acrylic resin-based RPD; Cobalt-chromium-based RPD; No treatment.
It is thus obvious that there will, for many years to come, be a need to select the treatment option of an 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 previously10 (Figure 4). 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:
Figure 3. The shortened dental arch of the mandible (opposing a maxillary complete denture) has been extended by CRRBs bilaterally. 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. 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: · Clasps: occlusally-approaching or gingivally-approaching; · Precision attachments: intra-coronal; extra-coronal; studs; bars and others (e.g. Ipso-Clip); · Guide Planes; · Planned use of soft-tissue undercuts. Clinicians will also be aware of the occasional beneficial effects of denture fixatives on unretentive dentures. NB The clinician is required to use a surveyor to identify and quantify undercuts and to plan paths of insertion etc. 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.
Figure 4. Changes in the number of hours spent in prosthodontic teaching laboratories, and numbers of C/C patients and RPD patients treated – over 40 years.
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 Kennedy1 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 3). 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. 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 reassessed as well as a determination of how the prosthesis/es may be maintained.
References 1. 2. 3. 4. 5. 6. 7. 8. 9.
Bowen RL. Adhesive bonding of various materials to hard tooth issues. Bonding to dentine, enamel and fluoroapatite by use of a surface active comonomer. J Dent Res 1965; 44: 906-911. Davis DM, Fiske J, Scott B et al. The emotional effects of tooth loss in a group of partially dentate people: a quantitative study. Eur J Prosthodont Rest Dent; 9: 53-57. John M, Slade GD, Szentpetry A et al. Oral health-related quality of life in patients treated with fixed, removable and complete dentures 1 month and 6 to 12 months after treatment. Int J Prosthodont 2004; 17: 503-511. Nuttall N, Steele JG, Nunn J et al. A Guide to the UK Adult Health Survey 1998. London: BDJ Books, 2001. Nasanni MZ. Treatment of the shortened dental arch: A survey of dentists' preferences, practise and patients' utility views. PhD thesis, University of Manchester. Kayser AF. Shortened dental arches and oral function. J Oral Rehab 1981; 8: 457-462. Jepson NJA, Thomason JM, Steele JG. The influence of denture design on patient acceptance of removable partial denture designs. Br Dent J 1995; 178: 296-300. Hussey, Lindon. (Hussey and Linden, 1996) Jepson N, Allen F, Moynihan P et al. Patient satisfaction following restoration of shortened mandibular dental arches in a randomised controlled trial. Int J Prosthodont 2003; 16: 409-414.
10. McCord JF. Understanding prosthodontics: where did it go wrong? Int Dent J 2003; 53: 335-339.