Prosthodontics

Esthetic considerations in the construction of a removable partial dentureOskar Sykora*

In the construction of a removable partial denture, the patient's interest frequently lies in theimprovement of his or her esthetic appearance. This desire can be underestimated by thescientifically trained dentist, resulting in a disappointed patient. The perimeters of potentialesthetic improvement might be infltienced by the limitations of each individtial case. However,appropriate care in the selection, arrangement, and position of teeth can overcome some ofthe limitations. This article describes the benefits of a well-planned, systematic approach toselection of the framework design, porcelain shade, and tooth mold as well as the baseftnish,and it illustrates, with specific examples, how to achieve the maximum esthetics in removablepartial dentureprosthodonties. (Quintessence Int 1994;25:757-762.)

Introduction

Esthetics can be defined as the branch of philosophydealing with beauty, especially with the componentsthereof: ie, color and form. Specifically, removable par-tial denture {RPD) esthetics could be defined as thecosmetic effect that affects the desirable beauty, charm,character, and dignity of the individual. No other partin dentistry is so important to the patient as the estheticcomponent of a prosthetic restoration. Yet, this es-thetic component may be underestimated by a dentist,or it may be delegated to a dental technician, who is fre-quently given an incomplete work authorization, withunforseen consequences.'"^

Esthetic considerations

The factors that influence the selection of the teeth fora removable partial denture are the pre-extractionrecords, the remaining natural teeth within the dentalarch and in the opposing dental arch, and the age of thepatient. The requirements for function and for es-

Professor of Prosthodonties, Department of Restorative Den-tistry, Dalhousie University, Factilt>' of Dentistry. Halifax. NovaScotia, B3H 3J5, Canada.

thetics will influence the arrangement of the RPDteeth. Finally, the factors that will influence the posi-tion of the teeth on an RPD are the horizontal relation-ship of the remaining natural teeth and the residualridges as well as the vertical positions of ocdnsal ,'iur-faces and incisai edges between the remaining naturalteeth and/or residual ridges and their relationship toanatomic landmarks.

Different shades, appropriate incisai translucency,and staining may be necessary to obtain a pet feet bletidwith the adjacent natural teeth. The mold of the se-lected teeth has to be compatible with the natural teethand he as long occlusogingivally as needed. The materi-al of both the RPD teeth and the denture base must bedurable as well as esthetic. While it may be said that"'beauty is in the eye of the beholder," the problem ofesthetics in the construction of a removable partialdenture can be summarized as "'what the patient wants,what the patient needs, and what the dental team iscapable of achieving."'

Framework design

Design for an RPD has to fulfill requirements forstability, support, and retention. The patient also ex-pects that the prosthetic restoration will improve his orher mastication, phonetics, and esthetics. In addition,the RPD has to maintain the health of the remaininghard and soft structures.

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Fig la Try-in of an RPD iramework. The anterior oaninewas set and indexed on the master cast prior to the waxupof the vertical retentive i o op.

Fig 1b The completed RPD harmonizes with the remain-ing natural teeth, the design protects the periodontal health,and the show of metal is minimized.

Fig 2a The restoration of a single maxillary central incisoron an RPD poses the most diffiouit esthetic challenge.

Fig 2b Esthetic success depends nol only on a propershade and mold seiection; characterization of the incisaiedge to harmonize with the attrition of the adjacent naturalteeth, slight interproximai grinding, and scoring of the mas-ter cast to achieve a tighter tissue adaptation of the RPDtooth aisc help to create an Jiiusion of reality.

Unfortunately, the esthetic factor is not always fullyconsidered when, for example, a ditect tetainer isplanned. This may result in a potentially questit^nableesthetic result from the patient's points of view. Figuresla and lb show the importance of harmonizing theframework design with the periodontal and es-thetic requirements. The position of an anterior RPDtooth may be compromised by an improper placementof the framework's latticework or by the improper lo-cation of a vertical retentive loop on the framework.Such an anterior RPD tooth must be set and indexedprior to the frame waxup,̂

Shade selection

Tlie present system, according to Preston, 'is incom-plete, lacks order, and is illogically structured," ' A deti-tal office may be well stocked with shade guides butmany problems remain unsolved. Some shade guidesdo not follow a logical pattern in number or graduationof Hue. Value, and Chroma.

Esthetic shade selection in removable partial den-ture prosthodontics poses a different and a difficultchallenge not encountered in the fabrication of com-plete or fixed partial dentures.^"'^ For example, wheti

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Fig 3 A maxiiiary first premolarshade guide can be custom made.

plastic teeth are indicated for a complete denture, ashade may be selected with a porcelain shade guide if aplastic one is not provided by the manufacturer. Theslight difference in the translucency, opacity, and colorbetween the selected porcelain shade guide tooth andthe delivered acrylic resin teeth on the complete den-ture will not be detected by the dentist or the patientbecause all of the denture teeth will harmonize witheach other. In fixed partial dentures, custom stainingwill allow the dentist to blend the basic shade to the re-quired esthetic harmony of the adjacent natural teeth.None of these advantages exist in the fabrication of re-movable partial dentures.

Particularly when matching a maxillary central in-cisor, the dentist cannot rely on the accuracy of a porce-lain shade guide, in spite of the assurances given by asalesperson or the manufacturer. The shade must be se-lected from a shade guide tooth made in the same ma-terial as the final product. Only then can a predictableesthetic result be assured (Figs 2a and 2b),

Shade selection for the posterior teeth presents anadditional challenge to overcome. This applies particu-larly to the replacement of a maxillary first premolar.This tooth, frequently for esthetic reasons, is consid-ered of equal importance as the six anterior teeth. Sucha tooth requires blending of different layers of mater-ial, as does an anterior tooth, to harmonize in the den-tal composition. However, no manufacturer providesthe dental office with a posterior shade guide, althoughthe majority of posterior acrylic resin teeth are not be-ing manufactured with the same gingival and occlusalblending as in the anterior teeth. Some natural poster-ior teeth do not even exist in anterior shades: someshades of posterior teeth show hardly a trace of thetranslucency that exists on a corresponding anteriorshade guide tooth. The easiest way out of this dilemma

Fig 4 Different types of acrylic resin teeth have vanous de-grees of transiucency, occlusai staining, and estethic ap-peal.

is for the dentist to make a custom posterior shadeguide'"" (Fig 3), The graying effect of some plastic pos-terior teeth can be detected and prevented with theproper selection of an appropriate acrylic resin tooth(Figs 4 and 5).

Mold selection

Placement of fewer teeth is often indicated for a tooth-borne edentulous space because the natural teeth havedrifted toward one another. Thus, it may be necessaryto select replacement teeth other than those lost by thepatient. For example, an artificial first premolar andfirst molar may be indicated for a space vacated by twopremolars and a first molar (Fig 6a), Tlie partial den-ture teeth must be as long occlusogingivally as thepalienfs adjacent remaining teeth to look natural; a

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Fig 5a Some aerylic resin teeth appear gray intraorally andthus do nof blend easily with the adjaeenf natural teeth.

Fig 5b PnDperly selected acrylic resin teeth should not beeasiiy disfinguisfiable from the remaining naturai teeth.

Fig 6a An appropriate mold seiection gives a harmoniousresult in spite of omission of a second premolar.

Fig 6b The mold seiection and the placement of the max-illary canine and molar BPD and the finish of the acrylic re-sin base do not blend with the adjacent nafurai teeth, result-ing in an unnatural and unesthetic appearance.

Fig 7 if fhe remaining natural teeth show recession of fhemarginal gingiva, the acrylic resin teeth and the base finishshould simuiate the recession.

Fig 8 The basio idea of a self-sanitizing RPO starts wifh anappropriate waxup around the distal-exlension base abut-ment tooth.

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Fig 9a The "abutment preparation" on the RPD frame ai-lows plaoement a custom-stained porcelain-tused-to-metaicrown.

Fig 9b The custom-stained porceiain-fused-to-metalcrown cemented on the inserted RPD frame is undetect-able, despite the patient's fiigh iip line.

shorter-t han-needed partial denture tooth may alsopresent an unwanted display of denture base material(Fig 6b).

Base finish

The contour of a partial denture base should harmon-ize with the remaining natural structures. Thus, for ex-ample, if the adjacent natural teeth show recession, thebase finish should reflect it (Fig 7). Likewise, in such atooth-supported design, the base is sometimes not es-sential on the labial or buccal aspect. Actually, omittingthe acrylic resin base altogether next to the mesialabutment improves not only the esthetics but also theperiodontal health of the abutment tooth. The inter-dental area is easier to clean and the design does notapply pressure on the periodontium because the firstRPD tooth has no base'' (Fig 8),

Finally, the interdental papillae of the RPD shouldbe in harmony with the interdental papillae of the re-maining natural teeth. If spaces exist, or existed,between the natural teeth, a diastema between theRPD tooth and the adjacent natural tooth is an ex-tremely effective way to create an illusion of reality(see Fig lb). These concepts are not new, Frush,"* in1957, brought the importance of the tooth matrix to theprofession's attention in an excellent study of dental es-thetics.

Special situations and helpful hints

• The shade selection for a missing maxillary central in-cisor in one particular patient proved to be a chal-

lenge because no manufactured acrylic resin toothmatched the color of the patient's adjacent teeth.Custom staining of a laboratory-processed acrylicresin tooth was not attempted because such a toothdoes not possess the necessary hardness of a top-quality manufactured resin tooth. The esthetic prob-lem was eventually overcome by creating a customporcelain-fused-to-metal pontic. which was attachedto the rest of the RPD framework (Figs 9a and 9b).The retentive framework components were designedto resemble a proximal amalgam restoration."

'Frequently the natural teeth must be modified,within the clinical acceptance level, to achieve the op-timal esthetic and functional requirements. This willfacilitate Ihe optimal position for the RPD teeth.These adjustments must be made prior to the com-mencement of the RPD treatment.

» Sometimes different shades of teeth have to be used;the left and the right sides may require different colorspecifications.

« The occlusal surfaces of RPD teeth must be altered toachieve optimal intercuspation against the opposingnatural teeth. The occlusal alteration is best donetooth by toolh, starting always with the artificialtooth adjacent to the mesial abutment. This modifica-tion of the cuspal inclines will improve the mastica-tory efficiency and the stability of the prosthesis andwill csthetically harmonize the occlusal wear patternof the RPD teeth to that of the remaining naturalteeth,

• In selected situations, a small amalgam restorationplaced within the occlusal surface of a mandibular

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first molar or a small buccal Class V restorationplaced on a second maxillary RPD tooth can createan illusion of harmony with the existitig restorationsof the remaining adjacent natural tocth.

•For a patient with a true skeletal Class III relation-ship, where natural teeth are in crossbite, to achievethe optimal function and esthetic result, a posteriorcrossbite tooth (eg, lvoclar K mold) should be cho-sen.

• To create the illusion that an anterior RPD tooth isplaced within the soft tissue, and not on top of it, themaster east must be scored. This will achieve a tighteradaptation of the acrylic resin tooth to the labial sur-face of the residual ridge.

Conclusion

A conttnuous study should be made of the pleasingcharacteristics of the natural teeth and their investingtissues. If these charaeteristics can be imitated in substi-tutes, an illusion of reality can be obtained. Dentistscan develop their artistic judgment by studying thecreative principles of the fine arts and the beauties ofnature.

The construction of a removable partial denture ne-cessitates the restoration of lost function: it should alsoimprove the phonetics, and it must maintain the healthof the remaining oral structures. However, it alsoshould improve the patient's overall cosmetic appear-ance and reconstruct anatomy in an esthetically pleas-ing way. To succeed, close cooperation between thedentist and the dental technician is required, and anunderstanding must be reached between the dentistand the patient as to what is feasible and possible toaehieve with such a restoration.

References

1. Brown ET. The dentist, the laboratory technieian, and Ihe pre-scription law. J Prosthet Dent 1965;15:1132-1138.

2. Calomeni AA. Problem areas encountered by dental labora.taries. J Prosthet Dent 1%8; 19:523-529.

.Í. DuttonDA. Standard abbreviations ¡and definitions) for use indental laboratory work authorizations. J Prosthet Dent 1972:27:94-95.

4. Giovanone A. The philosophy of cooperation of dentist anddenial laboratory processing technicians. Dent Lab News 1%3;25;3-7.

5. Henderson D, Fraser O. Communieating with dental laboratorytechnicians. Dent Clin North Am 1970:14;fiO3-615

6. Quinn t. Status of the dentai laboratory work authorization. JAm Dent Assoc 1959;79:U89-n9O.

7. Bates JF, Neili DJ. Preiskel HW. Restoration of the PartiallyDenlate Mouth. Chicago: Quintes,senee, 1984:84, %.

8. Sykora O. Set Lip of removable partial denture anterior teethprior to frame fabrication. Quintessence Denl Technolt<)86:10;369-37l).

9. Hirsch B, Levin B, Tiber N. The effect of patient involvementand esthetic preference on denture appearance. J ProsthetDentl972;28:127-132.

10. Levin E. Dental esthetics and the golden proportion. J ProsthetDenl 1978:40:244-252.

11. Lombardi R. The principles of visual perception and their clin-ical application to denture esthetics. J Prosthel Dent 1973;29:.158-3B2.

12. Preston JD. Esthetics and Color. Proceedings of the Sympo-sium on Ceramics. Chicago: Qnintessence, 1983.

13. Preston JD. A systemic approach to the control of estheticform. J Prosthet Dent 1976;35:393^02.

14. SykoraO. Fabrication of a posterior shade guide for removablepartial dentures. J Prosthet Dent 1983;50:287-2S8.

15. Karlsen K. Self-sanilizing partial denture. Stockholm: ABTandtekniska Laboratoriet, Bertil Aimer, 1972.

In. Frush JP A Study of the Dentogenic Concept of Dental Es-thetics and Dynesthetics. Swissedenl Foundation, 1957.

17. Sykora O. A custom-shaded poreelain-fused-to-metal restora-tion on a maxillary RPD. Quintessence Dent Tech ne I]987;11:187-189. H

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762 Quintessence International Volume25, Number 11/1994