Prosthodontics

Removable partial denture abutment restoration: A case reportillustrating a new direct tecbniqueWilliam H. Liebenbers*

The desiruction of the crown underlying a partial denture can render useless an otherwi.seacceptable prosthesis unless some means can be found for building up the tooth under theprosthesis. The aim of this article is to introduce a technique in which light-curing glass iono-mer resin cement is utilized for the direct restoration of removable partial denture abutments.The cavity preparation is completed in the customary manner. The cement is applied en masseand covered with a suitable translucent separating sheet. The denture is reinserted and therestoration is light cured from the perimeter of the abutment. Tlie denture is removed, and,with the aid of a suitable disclosing medium, the restoration is trimmed carefully to avoidredticing the intimate adaptation between the restoration and the removable partial denture.The technique is offered with full acknowledgment that it is a compromised treatment option.(Quintessence Int 7W5.-26.775-779.J

Introduction

A removable prosthesis must fulfill the basic principiesof bracing, retention, esthetics, support, and stability tobe successful.' To fulfill these principles, not only mustthe prosthesis be designed properly hut also the com-ponents of the prosthesis must adapt intimately tostructures in the mouth. This adaptation must be pre-served for the functional life of the prosthesis.

The adaptation to a restored abutment, in the case ofa removable partial denture (RPD) is best accommo-dated by cast gold, which can be carved to satisfy all re-quirements for support, stabilization, and retention.-Despite the best of intentions, the permanence or lon-gevity of any prosthetic restoration can never be as-sured because it is dependent on the changing charac-teristics of iiving tissues. Elderly patients commonlysuffer tooth fractures without trauma.' Excludingacute external trauma, the factors responsible for toothfractures are related to age changes in the dental tis-sues, the effect of previous restorations and caries, and

* Private Practice, Vancouver. British Columbia, Canada.Reprint requests; Dr William H. Liebenherg, Suite 201,2609 V/est-view Dri vi:. North Vancouver, British Columbia,V7N4M2, Canada.

occlusal disharmonies. Clinical observation suggeststhat the incidence of tooth fractures is increasing aspeople retain their teeth for ionger periods.'' Tlie de-struction of the crown underlying a partiai denture canrender useless an otherwise acceptable restoration un-less some means can be found for restoring the toothunder the prosthesis.

The aim of this article is to introduce a technique inwhich light-cnring glass-ionomer resin is utilized forthe direct restoration of RPD abutments. In light of thelack of long-term clinical studies, the technique is of-fered with full acknowledgment that it is a compro-mised treatment option. As such, it is reserved for pa-tients for whom the optimum treatment of a cast resto-ration together with a new or repaired RPD is withheldfor one reason or another.

Case report

A 72-year-old man presented with generalized severeabrasion of both arches and a chief complaint of sensi-tivity to pressure in the mandibular right quadrant. Theabrasion resulted from frictional wear and repeatedcontact with the opposing arch during bruxism. Thedentition displayed classic concave abrasive deteriora-tion of the occlusal surfaces, and the dentin had wornmore quickly than the enamel (Fig 1). An overlay re-

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movable partial denture was fitted about 14 years pre-viously and had been adequately supported by the fiveremaining mandibular teeth. The maxilla was restoredwith a similar appliance.

The patient reported that the prostheses had beentrouble-free up to a few months previously, at whichtime he had experieticed sensitivity to pressure in theregion of the mandibular molar, A visit to a dental of-fice had resulted in a repair to the mesial rest seat area.The sensitivity persisted and the denture no longer fit-ted as snugly following the repair of the exposed dentinof the tnesial rest seat. Clinically it was possible to dis-place the alloy restoration with a blunt explorer. Al-though there was severe loss of periodontal supportingstructures, pocket formation was shallow and toothmobility was unremarkable.

The patient stressed his limited resources and dis-played hmited psychological endurance to undergo the"optimal"' restorative solution. It was decided to retainthe existing RPD because the patient was satisfied withhis prosthesis. Informed consent was obtained for a di-rect technique, subsequent to the mandatory disclosureof the trial nature of the procedure. At the very worst,the repair would serve as an interim restoration untilthe patient couid afford a more definitive restoration,at which time the repair would form the eore for a eastabutment.

Technique

The severely compromised molar abutment of the pa-tient in this case report (Fig I) was chosen to documentthe technique because it demonstrates both the scopeand adaptability of this direct restorative method.

After local anesthesia is obtained, the tooth is isolat-ed to permit caries removal and pin placement. Pulpalprotection is accomplished where appropriate (Fig 2),A matrix is applied and 10% polyaerylie acid effects thenecessary smear layer removal. Ketac-Silver (ESPE)was chosen to restore the distal aspect of the restora-tion because it sets through a chemical reaction andlends itself to ancillary pin anchorage. A hght-curingglass-ionomer-resin cement (GC America) was chosenfor the occlusal portion of the restoration because thepolymerization mechanism allows for greater controland manipulation of the material. In addition, proper-ties such as wear resistance and fracture toughness ofthe completely set glass-ionomer-resin cetnents are re-portedly superior to those of self-hardening glass-iono-mer restorative cements,'

The first layer of light-euringglass-ionotner-resin ce-

ment is applied and cured after rubber dam isolation tsestablished (Fig 3), The rubber dam is removed atid theexeess silver cermet is trimmed with a flut'. ' .ibtdebur used under air-water spray at low speed, •-'-'•• R r üis then reinserted and cheeked for fit (Fig 4) .̂ nd therestoration is again trimmed where necessary.

Following placement of cotton roll isolation, a sec-ond layer of light-curing giass-ionomer-resin cement isapplied en masse to the abutment (Fig 5), A square oftranslucent latex or cling film is immediately drapedover the entire cement-covered abutment. This is thecritical part of the technique, as the RPD is reinsertedand the glass-ionomer is exposed to visible light fromthe perimeter of the draped and engaged tooth (Fig 6),The drape retains the material and allows it to occupythe void between the tooth and the RPD, while it pre-vents the material from flowing over the clasp arm as-sembly.

The RPD is removed and polymerization is repeatedwith full surface access to ensure adequate cure. Theexcess material now must be removed, A square ofAcu-film tape (Parkell) is placed inside the inner sur-face of the RPD (in theimmediate vicinity of the resto-ration) and the RPD is reseated in the mouth. TheRPD is removed and the restoration is trimmed care-fully so that the critical regions (rest seat, guidingplane, and the contacts for reciprocal and retentiveclasp arms) previously marked with the disclosingmedium are not reduced.

This marking, insertion, removal, and trimming pro-cess is repeated until the surface contacts at the tooth-frame interface are restored to acceptable limits (Fig7), One of the advantages of using a light-curing mate-rial is that additional material can be added to those re-tentive surfaces inadvertently reduced during the fin-ishing stages.

The oeelusion is checked with the prosthesis in place.The patient is reminded of the possibility that he or shemay require definitive treatment in the future (Fig 8).

Discussion

Management of RPDs in an age of restorativeexcellence?

Because it is less expensive and in many instances sim-pler than the fixed bridge, the RPD continues to be apopular appliance in the managementof the elderly,partially dentate patient. This management includespreventive and restorative maintenance of the re-maining abuttnent teeth. The beneficial role of repairs

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Fig 1 In a 72-year-oid patient, the ailoy restoration of amandibular abutment tooth, supporting an otherwise satis-factory overlay removable partiai denture, is defective.

Fig 2 The tooth is isolated with rubber dam. the defectiverestoration is removed, caries is debnded, anciiiary pins areplaced, and pulpal protection is achieved with a calcium hy-droxide iiner.

Fig 3 The distal portion is filled with silver-cermet cement.The initiai layer of the glass-ionomer-resin cement is bond-ed to the autocured base of silver-cermet cement. The rub-ber dam is removed to SLWOVJ for the reinsertion of the RPDand the completion of the direct restoration.

Fig 4 Theoveriay RPD IS checked for fit. The newly addedKetac-Silver portion of the restoration is impeding the fullengagement of the linguai ciasp. This portion is trimmedwith a fiuted carbide bur used under air-water spray.

Fig 5 The bulk of the glass-ionomer-resin cement is ap-plied in one overfiiied portion, A square of translucent iatexor cling fiim is immediately draped over the entire cement-covered abutment. The RPD is then reinserted.

Fig 6 The drape is intended to retain the cement and pre-vent the cement from sticking to the RPD during polymer-ization. Visible iight is then applied from the perimeter of thedraped and engaged tooth. The RPD is removed and poly-merization is repeated with full surface access.

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Fig 7 Articulator ribbon is placed inside the RPD, and theBPD is reseated in the mouth. The RPD is removed and therestoration is trimmed caretuily so as not to reduce the criti-cal regions previously marked with the disclosing medium.The immediate distai view demonstrating the stratifiednature of the restoration is shown.

Fig 8 This restoration will serve as an adequate interimrestoration untii the patient is abie to afford a cast abutmentrestoration, at which point it wiii function as a reliable core.

to faulty complete dentures has previously beenbrought to the profession's attention."* Similarly, re-pairs to abutments in partially dentate individuals canprovide beneficial and cost-effeetive treatment.

This is particularly pertinent in light of an increasing-ly elderly population, in whom advanced looth wear isprevalent and likely to increase.'' It is therefore incum-bent on clinicians to learn how to extend the functionallife of existing RPDs by restoring defective abutmentsin a simple and eosi-effcctive manner.

Treatment modalities for defective abutments in theelderly include complete neglect, extraction, direct re-pairs, and the fabrication of a new indirect restorationtogether with the fabrication of a new or repaired pros-thesis.

The decision to sacrifice ralher than restore and toignore rather than replace should always be based onsound treatment planning after all available alterna-tives are considered, so as not to deprive the geriatricpatient of optimum care.' For individuals for whomcost is a primary concern, the direct reconstruction ofthe abutment tooth as a reliable interim restoration canbe a most important option.

Direct reconstruction of the abutment tooth

Satisfactory reconstruction of the severely compro-mised abutment tooth is "easily" achieved with alloy ifone is prepared to discount the retrofit adaptation of

the RPD on reinsertion. In clinical practice, the short-coming of using the direct technique with traditionalmaterials relates mostly to the resultant RPD-abut-menl adaptation, which is unpredictable and best de-scribed as a hit-and-miss exercise. Stern et al** measuredthe eontact between the rests of clinically acceptableRPDs and abutment teeth, and demonstrated that 20%of the rests did not contact the rest preparation. It maythen be tempting to attempt direct reconstruction be-cause the rest area ean be carved on a trial and error ba-sis until the RPD returns to its original position. How-ever, in severely compromised abutments, the "resto-ration'" of the original path of placement, proximalguiding planes, and stjitable retentive areas is more of-ten than not unachievable. The intimate adaptationbetween the abutment and the RPD is reduced to ap-proximation, and compromised function, with little ifany frictional resistance to dislodgment at the tooth-frame interface.

Retention is invariably reestablished through agreater reliance on clasp retention. This is achievedthrough redirection and manipulation of the clasps.With an RFD, functional movements are magnified bythe components and are transmitted to the abutmentleeth by the clasps. In addition to the obvious complica-tion of elasp breakage or distortion,'' increasing theforceoftheclasp to enhance retention may also be det-rimental to the periodonlium beeause of the additionallateral forces placed on the abutment teeth.'""'-

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Vitreiner as an alternative material

Vitremer tri-eitring glass-ionomer system {3M Dental)was introduced in March 19i-)3 and is the ideal materialfor this technique because of its unique polymerizationprocess- Additional methacrylate curing takes placewithout light exposure because of the patented reduc-tion-oxidation (redox) catalyst system,'^ The dark cur-ing might be important in larger restorations, in whichthe depth of light penetration is uncertain and whereancillary pin anchoraj^e is employed. Its use would cer-tainly have simplified ihis "stratified" cerment ap-proach.

Aeknuwledgments

The author would like to acknowledge his chairside assistants, MsKerry Cheyney and Ms Daphne Roberts, tor assistance in the oper-ators procedures depicted in this article.

Rfftrences1, Wong MX Cah'erley MJ, Nag>' WW. Removable partial den-

ture framework try-in, J Prosthet Dent 1993:69:363-368,2, Henderson D, McGivney GP, Castieberry DJ, Me Crackcn's

Removable Partial Denture Construction, ed 5. St Louis: Mos-by, 1977:220.

3, Ibbetson RJ, Restorative needs and methods. In: Cohen B,Thompson H |eds). Dental Care for the Elderly, London: YearBook Medical, 1987:141-177,

4, Iacopino AM, Wathen WF, Gerialric prosthodontics: An over-view. Part 2. Treatment considerations. Quintessence IntÍ993;24:353-361,

5, Croll TP, Light-hardened Class 1 glass-¡unomei-resin cementrestoration of a permanent molar, Quintessence Int iy'J3-24:109-113.

6, Hand JS, Beek JD, Turner KA, The prevalence of ocelusal attri-Uoii and considerations for treatment in a non-institutionalizedolder population. Spec Care Demist I987:7:2U2-2O6,

7, Liehenberg WH, Geriatric restorative care—compromise orexcellence: A case report. J Dent Assoc South Afr 19<J3:48:417^21,

8, Stern MA. Brudvick JS, Frank RP Clinical evaluation of re-movable partial denture rest seat adaptation, J Prosthet Dent

9, Anderson JN. Bates IV. The cobalt chromium partial denture:Clinical survey, Br Dem J 1959:107:57-62,

10, KyJd WL, Dutton DA, Smith DW. Lateral forces exccrtcd onabutmenL teeth by partial dentures, J Am Dent Assoe 1964:68:859-863,

11, Clayton JA.JaslowC A measurement of clasp lorces on teeth,JProsthetDent 1971:25:21-143,

12, Maxfielcl JB, Nicholis Jl, Smith DE, The measurement of forcestransmitted to abutment teeth of removable partial dentures,J Prosthet Dent 1979:41:134-142,

13, Croll TP, Killian CM, Class 1 and Class 2 light-hardened glass-ionomer/resin restorations, Compend Contin Educ Dent 1993:7:90S-916. D

25th International Meetingon Dental Implants and Transplants

Bologna (Italy), May 26-28,1995

The event of the year!Information: G.I.S.I. c/o Prof. G. Muratori

1, Via S. Gervasio, 40121 Bologna (Italy), Tel. 39 51/22 75 05-23 7516, Fax 39 51/2600 31

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