A Clinical Overview of Removable Prostheses_Introduction 1.Factors to Consider in Planning a Removable Partial Denture

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A Clinical Overview of Removable Prostheses: Introduction J. FRASER MCCORD, NICK J.A. GREY, RAYMOND B.WINSTANLEY AND ANTHONY JOHNSON

Abstract: This series of articles has been written with the intention of simplifying the processes involved in the prescription of removable partial dentures. The scene is set in this introduction, and the first article addresses basic clinical and patientrelated factors involved in decision-making before commencing active prosthodontic treatment. The second paper will outline a variety of impression techniques for primary and definitive impressions, while the third discusses designing principles. The fourth article is a brief overview of some technological aspects of removable partial denture-making and the fifth attempts to provide a useful guide showing how to diagnose and manage common clinical problems associated with removable partial dentures. Dent Update 2002; 29: 375

Clinical Relevance: The provision of satisfactory removable prostheses is an important aspect of dental practice.

he decision to replace missing or extracted teeth may be made for a variety of reasons. The ultimate decision, however, will in all probability be predominantly, but not exclusively, patient-driven. Clearly, the clinician has a considerable part to play in advising the patient on the merits or otherwise of restoring missing teeth and, further,

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J. Fraser McCord, BDS, DDS, FDS, DRD RCS (Edin.), FDS RCS (Eng.), CBiol, MI Biol, Professor and Head of Unit of Prosthodontics, University Dental Hospital of Manchester, Nick J.A. Grey, BDS, MDSc, PhD, FDS, DRD, MRD RCS (Edin.), Consultant/Honorary Senior Lecturer in Restorative Dentistry, Edinburgh Dental Institute, Raymond B.Winstanley, BDS, MDS, FDS RCS (Edin.), Senior Lecturer/ Honorary Consultant in Restorative Dentistry, Charles Clifford Dental School, Sheffield, and Anthony Johnson, MMedSci, PhD, Lecturer in Dental Technology, Charles Clifford Dental School, Sheffield.

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has a leading part to play in how to replace teeth. This subject becomes a matter of debate among clinicians and technicians and, while most clinicians may agree on whether a prosthesis should be fixed or removable, the nature of the design will often be subject to considerable variation. This is particularly true in the case of removable partial dentures (RPDs) or, more accurately, removable prostheses. As Watt and Macgregor stated,1 this is because many features that are desirable in RPDs ‘are mutually exclusive and the process of designing is a journey through a maze of compromises’. It is not difficult to understand why student clinicians struggle over the intricacies of RPD design given their relative inexperience in the treatment of patients; it is a matter of frustration to teaching prosthodontists, however, that most clinicians either find it

beneath their dignity to design RPDs or find that designing them is problematic. Whatever the reason, many clinicians devolve the responsibility of denture design to the technician. Most textbooks on what to do when a patient presents with missing teeth are aimed at undergraduates and assume the role of either a textbook on fixed prostheses or a textbook on RPDs. The intention of this series of articles is to serve as a clinical manual for graduate clinicians who are operating at a non-specialist level, with the following purposes: l to share our views on how to plan and organize treatment; l advise on how to structure decision making; and, when these two qualifying rounds are completed; l to discuss rationales of design principles for RPDs. We will also address technical aspects of RPD treatment and, in conclusion, address problem solving. We are firmly of the view that the clinician should lead the dental team and that this leadership should include responsibility for designing RPDs appropriate to the needs of each patient.

R EFERENCES 1.

Watt DM, MacGregor AR. Designing Partial Dentures. Bristol: Wright, 1984.

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A Clinical Overview of Removable Prostheses: 1. Factors to Consider in Planning a Removable Partial Denture J. FRASER MCCORD, NICK J.A. GREY, RAYMOND B.WINSTANLEY AND ANTHONY JOHNSON Abstract: This is the first article in a series on the prescription of removable partial dentures. It addresses basic clinical and patient-related factors involved in decisionmaking before commencing active prosthodontic treatment. Further papers will outline a variety of impression techniques for primary and definitive impression, discuss designing principles, give an overview of some technological aspects of removable partial denture-making and provide guidelines on how to diagnose and manage common clinical problems associated with removable partial dentures. Dent Update 2002; 29: 376-381

Clinical Relevance: Good planning is essential for the satisfactory removal of partial dentures.

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he need to restore teeth in edentulous space depends on a variety of clinical issues and the wishes of the patient, which may relate to: l l l l l l

aesthetic factors; function; occlusal stability; comfort; speech; prevention of further disease/ deviations from normal;

J. Fraser McCord, BDS, DDS, FDS, DRD RCS (Edin.), FDS RCS (Eng.), CBiol, MIBiol, Professor and Head of Unit of Prosthodontics, University Dental Hospital of Manchester, Nick J.A. Grey, BDS, MDSc, PhD, FDS, DRD, MRD RCS (Edin.), Consultant/Honorary Senior Lecturer in Restorative Dentistry, Edinburgh Dental Institute, Raymond B.Winstanley, BDS, MDS, FDS RCS (Edin.), Senior Lecturer/Honorary Consultant in Restorative Dentistry, Charles Clifford Dental School, Sheffield, and Anthony Johnson, MMedSci, PhD, Lecturer in Dental Technology, Charles Clifford Dental School, Sheffield.

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expecting; at this stage it may be obvious that their demands are unrealistic or might result in a situation that compromises other factors relevant to denture-wearing success. The following aspects of aesthetics should be considered when planning any prosthesis:1 l l l l l l l

colour; contour; proportion; symmetry; outline form; soft-tissue harmony; and position of the teeth.

l psychological factors. Unless any one of the above reasons can clearly be justified, there is little reason to provide interventive treatment. It is often said of removable partial dentures (RPDs) that ‘the best kind of partial denture is no partial denture’, as many studies have demonstrated the untoward effects of their presence in the mouth. The need to provide treatment (RPD) will therefore be explored within each of the above subject headings.

AESTHETICS The old adage ‘beauty is in the eye of the beholder’ is often recounted and, unless the wishes of the patient are considered at the outset of planning, the potential for failure is very high, with consequent ill-feeling between patient and clinician, and sometimes the technician. At the initial consultation, therefore, care should be taken to determine exactly what the patient is

RPDs have the potential to control aesthetics significantly better than fixed prostheses (either tooth-supported or implant-supported) as all of the above aspects may be addressed. To avoid aesthetic problems, the clinician must plan where the teeth are to be placed in the prosthesis in advance of planning the other components of the denture, especially if a cast cobalt chromium framework is being prescribed. If this planning is not performed the morphology of the framework may dictate tooth position, which may in turn compromise the appearance of the denture and be at variance with the patient’s wishes. This will be discussed in a later article. Another helpful stage during denture construction is that of allowing the patient to take the trial insertion prosthesis (or a wax-up of the proposed prosthesis) home to allow a longer evaluation with family and/or friends. This gives the patient greater input during his/her treatment, Dental Update – October 2002

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Figure 1. Placement of an ‘I’ bar on the distobuccal aspect of the abutment tooth diminishes the unsightly nature of the clasp.

which reduces the need to alter the appearance of the denture after fitting. The situation of having to alter the denture in any way after delivery of the denture is disappointing for all concerned, and any opportunity to avoid doing so should be taken.

Visibility of Clasps A common problem with the aesthetics of RPDs relates essentially to what is often perceived as the unsightly display of clasps. Wherever possible, the more posterior a clasp can be placed, the more unlikely it will be that appearance is compromised. However, this is not always a realistic option and therefore clasping should be disguised as much as possible – Figure 1 shows the distolabial placement of an ‘I’ bar to minimize the display of metal. Other methods described have been those of utilizing materials for clasping which are tooth-coloured and potentially ‘more aesthetic’. One such system is the ‘Dental D’ clasp system (Figure 2). This system would appear to be well

Figure 2. The ‘Dental D’ clasp. Note the proximity of the clasp arm to the gingivae. The authors do not recommend this type of clasp: hence this is a laboratory model and not a clinical case. Dental Update – October 2002

accepted by patients but does require rather long, thick clasps, which are often inappropriately close to the gingival margin. In addition, repair of these clasp arms is more technically demanding and this has of necessity a cost implication. The use of precision attachments can also be considered; however, this requires a significant amount of interocclusal space, which is often not present. In addition, maintenance of precision-retained prostheses is exceedingly problematic. Although precision attachments are undoubtedly useful components, conventional wisdom would suggest that the clinician and the technician have some experience in their usage and (of great importance) their maintenance. A very useful method of dispensing with or reducing the number of clasps is to use hard or soft-tissue contours (undercuts relative to paths of survey) that may be present in the anterior part of the mouth. For example, where an anterior bounded saddle exists, the clinician and dental technician should survey the casts to consider the possibility of using an anterior path of insertion by tilting the casts upwards in the anterior region, enabling the prosthesis to engage that undercut and resist displacement relative to the occlusal path of displacement. Retention may be enhanced and the overall appearance improved as the denture/ tooth interface may be better managed, avoiding unwelcome gaps (Figure 3). Similar problems exist in the presence of other saddles in the arch, although appearance may not be as critical. Another technique for avoiding the use of clasps is to utilize a resilient material adjacent to the dental undercuts. This may engage the undercut and gain retention (Figure 4). However, although this technique is useful, the long-term stability of such materials is less ideal than hard acrylic, and the clinician and patient need to be aware of the need to replace the material periodically. This clearly has cost and social implications as the patient will be without his/her denture for at least a working day to enable the technician to effect the replacement.

Figure 3. By planning the path of insertion, the flange on |2 merges imperceptibly with the gingivae of the canine.

Figure 4. A resilient lining was incorporated into this training denture to engage the undercut in the distal aspects of the abutment teeth. It provided retention, stability and avoided the unsightly presence of clasps.

Matching Artificial to Natural Teeth Problems may be encountered when attempting to match the colour of artificial teeth to the natural ones. The greatest area of difficulty is often with respect to differences in crown heights and the careful selection of denture teeth is advised to avoid a ‘step’ (Figure 5) caused by the denture teeth having shorter clinical crowns than the natural teeth.

Figure 5. No thought had been given to the gingival architecture adjacent to the necks of the teeth. 377

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FUNCTION The decision as to whether treatment is needed to satisfy efficient masticatory function is often dictated by the patient and a number of studies have investigated patient satisfaction with respect to the remaining number of teeth. Kayser2 and Witter et al.3 introduced the concept of accepting a shortened dental arch rather than providing interventive treatment if periodontal health and tooth position are deemed to be stable. Other studies have investigated patient satisfaction of shortened dental arches and it is apparent that there is not always a need to replace teeth to increase the number of occluding units. In situations where, for example, first premolar to first premolar teeth exist in opposing arches, appearance may be compromised more than function. The placement of distally cantilevered pontics from the first premolars has been described;4 the success of such a technique is reportedly high, and it is therefore worthy of consideration (as an alternative to doing nothing or providing an RPD) during treatment planning. The delivery of treatment that will do no harm to the patient is of great importance and the practitioner must balance the likelihood of an appliance increasing function against the potential for it to be an agent of iatrogenesis. When planning an RPD, mouth or tooth preparation may be required and there is a risk that, should the patient be unable to tolerate the appliance, he or she has undergone unnecessary treatment which may render them worse

Figure 6. Patient needs (e.g. ripping action of the chipped incisors on food) ought to be determined before any tooth tissue is removed.

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off. An example may be seen in Figure 6. In this case, the worn anterior teeth were reduced before making master impressions for an upper overdenture. It transpired that the patient could not tolerate the appliance and did not wear the overdenture. With respect to function, the patient perceived the treatment a failure, as previously he had used the sharp edges of the worn anterior teeth to ‘rip up’ his food. One way of avoiding such an outcome would have been to fabricate a diagnostic appliance before resorting to irreversible measures such as tooth reduction. If the patient had accepted the diagnostic appliance the clinician could have proceeded with greater confidence about the outcome of the treatment.

OCCLUSAL STABILITY Although it is often discussed, the concept of what constitutes occlusal stability is not well defined and instability can often be diagnosed only when difficulties arise from occlusal changes. In this respect, the philosophy of restoring a recently created space to maintain occlusal stability (especially in the opposing arch) merely to avoid the potential for unwanted tooth movements has no evidence base. We would urge that the clinician monitors each case and consider intervention only when changes appear to be occurring. Should occlusal changes be noticed, the nature of the prosthesis to effect further change must also be taken into account. For example, a mucosa-borne prosthesis may ultimately sink into the tissues and be out of occlusal contact, therefore proving ineffective both as a preventive measure and as a functioning prosthesis (Figure 7). There is always the potential for teeth to tilt or drift following tooth extraction and such changes are probably of more concern where appearance is compromised. Figure 8 shows a situation where, following tooth extraction, no prosthesis was worn and tooth movements have resulted in a space more difficult to

Figure 7. The mucosa-borne denture which was worn has resulted in further loss of the alveolar bone. In addition, the lower incisors have overerupted.

restore without resorting to orthodontics.

COMFORT If a patient presents with pain or discomfort, a non-interventional approach obviously cannot be considered and the treatment strategy should be to address the difficulty. Disease control and its management is well reported and requires little further discussion; however, there are several options for management of discomfort from an RPD. The advantages and disadvantages of each option should be discussed with the patient so that he or she can make an informed decision on how to proceed with treatment.

Modification of the Existing Prosthesis Modification of an existing prosthesis may often appear attractive to both the dentist and the patient as the number of visits is considerably reduced.

Figure 8. Before definitive treatment could be performed, the space for the canine had to be increased orthodontically.

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Where alveolar resorption has occurred, a reline procedure may effectively rejuvenate the impression or ‘fitting’ surface of an otherwise satisfactory appliance. However, great care needs to be taken before modifying a previously worn prosthesis as the changes made might not result in an improvement as far as the patient is concerned – and may even make the situation worse (e.g. the patient may have a problem relating to tissue support in the denture-bearing saddle areas). At this stage, the dentist and patient may have reached an impasse as the situation is irreversible.

Changing the Design of the Appliance or Technique of Fabrication A later article in this series will attend to the diagnosis of partial denture problems, and the importance of making an accurate diagnosis cannot be overemphasized. Good diagnosis should lead to appropriate treatment planning. The maxim ‘no diagnosis, no treatment’ is entirely true here.

Consideration of a Fixed Appliance If a removable partial denture has been worn by the patient but was unsatisfactory in terms of comfort (although the denture, normatively speaking, was acceptable) then consideration could be given to the use of a fixed partial denture. The clinician must balance the relative benefits of resorting to a fixed option against the potential disadvantages. The preparation of teeth for ‘conventional’ bridgework tends, per se, to be destructive of tooth tissue, whereas resin-retained bridges are much less so, and the clinician should determine which form of fixed prosthesis is most appropriate for the patient.

Consideration of an Implantretained and/or Supported Prosthesis The use of dental implants should be 380

taken into consideration when the strategy for treatment is being developed, and in most cases should feature in the list of options presented to the patient before obtaining informed consent. Further details of considerations of implant therapy are contained in appropriate textbooks, but obviously multiple-bounded saddles, medical reasons or cost might indicate that RPDs are selected over implants.

Rendering the Patient Edentulous In some circumstances, the number and anatomical distribution of the remaining teeth is such that the wearing of an RPD with comfort is rendered more difficult. This situation often exists when only a few teeth remain in the arch. These teeth may offer little benefit in terms of support for the prosthesis and the opportunity for retention offered by these teeth may often be less satisfactory than if a complete denture was provided with the full benefits of a complete peripheral seal. From this perspective, therefore, although this option may appear destructive, extraction of the remaining teeth may be beneficial, although the patient’s perceptions must be taken into account. If the patient has some standing teeth in the mandibular arch plus a mandibular RPD, then the possibility of achieving predictable success (combination syndrome) is problematic.5

Factors Relating to Comfort of RPDs Several factors relating to comfort may be considered. Impression Technique Discomfort may be related to the ability of the denture-bearing area to support a prosthesis. Thin and friable mucosa, flabby ridges and the presence of undercuts present particular difficulties. As a later article in this series describes techniques to take into account the different problems to be considered, the

subject is listed here only for thoroughness. Design of the Framework The design of the major connector may be important for the comfort of the patient. The extent of palatal coverage may compromise this if there is a susceptibility to gagging. In addition, the way the prosthesis is perceived by the soft tissues, especially the tongue, may affect patient tolerance. Opinions differ as to the optimum design of major connectors, but in our view the decision on the major connector should be reached only after thorough assessment of the patient and taking his or her wishes into account. Materials Used Cobalt chromium (in definitive prostheses) is generally better accepted by patients than acrylic, as transmission of heat and less bulk have been deemed preferable.6 The presence of an allergy to a dental material is important and, although rare, often makes the treatment problematic for the dentist as confirmation of the allergy may prove difficult. Allergies to acrylic (PMMA) and nickel appear to be the most common and manufacturers offer alternative materials for such cases. The Need for Mouth Preparation The patient may present with discomfort that requires management before an impression can be made. Denture stomatitis may best be managed by asking the patient to abstain from wearing the appliance. This suggestion, however, is rarely welcomed by the patient and may result in considerable social distress; it is therefore not always a sensible option. In such circumstances, the use of (for example) miconazole gel on the fitting surface of the denture can be employed – but this is contraindicated for patients taking anticoagulants (e.g. warfarin).

Further Considerations On a historical basis, pre-prosthetic Dental Update – October 2002

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Figure 9. The palatogram indicates where the tongue contacts the denture base and teeth.

surgery was often considered in the hope that the denture-bearing area could be improved. The use of such procedures is now quite rare as the outcome is not predictable and subjecting a patient to surgery where this is the case must be difficult to justify. (For the purposes of this series of articles, alteration in form to the natural teeth is not considered preprosthetic surgery, but preparation of the mouth.) Whenever the dentist has concerns about the state of health of the oral tissues it is wise to refer the patient for an oral medicine consultation to ensure that no underlying disease exists. This is especially pertinent where an apparent denture-related ulcer fails to heal 1 week after leaving a denture out of the mouth.

SPEECH Speech difficulties appear to be quite uncommon in dentistry and, in the authors’ experience, have constituted a small percentage of new patient referrals to consultation clinics in the Dental Hospitals of Edinburgh, Manchester and Sheffield. Although they are exceedingly rare, speech difficulties can cause the dental practitioner much difficulty. Several studies have described the phonetic determinants of speech in dentistry, paying particular attention to the clinician’s awareness as to the significance of sibilant sounds and labiodental sounds.7,8 Many potential difficulties of both fixed and removable prosthodontics can be overcome by using a provisional appliance to assess the acceptability of Dental Update – October 2002

the prosthesis to the patient before embarking on a definitive solution. When speech difficulties do occur they are often transient, but if persistent soft wax or pressure-indicating paste may be applied to the prosthesis as a diagnostic tool. This may reveal what features of the appliance need to be altered in order to identify tongue contact areas and help determination of the effect of decreasing the space on airflow in anterior consonant phonetics (e.g. S, Ch, Th; Figure 9).

perceive such a situation as socially unacceptable. In such cases, he or she may demand a fixed solution such as the placement of dental implants.12 Where such psychological difficulties exist, management should involve consultation with appropriately trained personnel, although the dental practitioner might have problems if access to such personnel is limited. The dental practitioner should try to take on this role only with great caution.

SUMMARY PREVENTION OF FURTHER DISEASE/DEVIATION FROM NORMAL The need to place a restoration is more straightforward when it is quite apparent that by not doing so a worse scenario would ensue. For instance, it could be that teeth, after a period of time of monitoring, are over-erupting and at that stage provision of an appliance may be appropriate. Furthermore, if toothwear is progressive, resulting in shorter crown heights, the eventual provision of fullcoverage restorations is made more difficult. In such circumstances the placement of a removable restoration would be justified. Overall plaque control is a basic prerequisite of all preventive regimens.9,10 With prevention in mind, therefore, the clinician should always remember the maxim of Watt and MacGregor:11 ‘the design of partial dentures should avoid the intricate and complex in favour of the tidy and simple’.

PSYCHOLOGICAL FACTORS There are many reasons other than obvious dental difficulties that may make the provision of a satisfactory removable prosthesis difficult or even impossible. Most commonly, gagging represents a difficult situation to rectify. Various methods of addressing this issue have been reported, such as desensitization programmes, hypnosis, the use of relative analgesia and even acupuncture. Another problem is that some patients reject the idea of wearing a removable appliance because they

This article has outlined whether interventional treatment for a patient with edentulous spaces is warranted. Generally, unless the practitioner can confidently be assured that one of the above-noted categories necessitates treatment, little should be done.

REFERENCES 1.

Cassidy M, McLaughlin WS, Grey NJA. Aesthetics and porcelain veneers. Restor Dent 1989; 5: 42– 45. 2. Kayser AF. Limited treatment goals – shortened dental arches. Periodontology 2000 1994; 4: 7–14. 3. Witter DJ, van Palenstein Heldeman WH, Creugers NH, Kayser AF. The shortened dental arch concept and its implications for oral health care. Community Dent Oral Epidemiol 1999; 4: 249–258. 4. Al-Wahadni A, Linden GJ, Hussey DL. Periodontal response to cantilevered and fixed-fixed resin bonded bridges. Eur J Prosthodont Restor Dent 1999; 7: 57–60. 5. Kelly E. Changes caused by a mandibular removable partial denture opposing a maxillary complete denture. J Prosthet Dent 1972; 27: 140– 150. 6. Anusavice KJ. Phillips’ Science of Dental Materials, 10th edn. Philadelphia: WB Saunders, 1996. 7. Lawson A, Bond EK. Speech and its relation to dentistry. Dent Pract 1968; 19: 113–118. 8. McCord JF, Firestone H, Grant AA. Phonetic determinants of tooth placement in complete dentures. Quintess Int 1994; 25: 341–345. 9. Bergman B, Hugoson A, Olsson CO. Caries, periodontal and prosthetic findings in patients with removable dentures: A ten-year longitudinal study. J Prosthet Dent 1982; 48: 506–514. 10. Mullally BH, Linden GJ. Periodontal status of regular dental attenders with and without removable partial dentures. Eur J Prosthodont Restor Dent 1994; 2: 161–163. 11. Watt DM, MacGregor AR. Designing Partial Dentures. Bristol: Wright, 1984; p.201. 12. British Society for the Study of Prosthetic Dentistry. Guidelines in Prosthetic and Implant Dentistry. London: Quintessence Publishing, 1996.

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