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8/2/2019 ally Treated Teeth as Abutments

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RESTORING ABUTMENT TEETH

occlusal rest (Fig. 5, B), and guiding planes (Fig. 5, C).If there are voids or irregularities, they are filled withmonomer and powder with a paint brush.

9. Try-in the removable partial denture (Fig. 6 ) toensure a proper adaptation of the resin coping (Fig. 7).The die spacer can be removed from the tooth witha cotton pellet soaked in die spacer thinner. Rinse thetooth several times before cementing the temporaryrestoration.10. Transfer the resin coping to the working stone dieand finish the margins with wax (F ig. 8). If the surfaceof the resin coping is not smooth, paint it with a thinlayer of liquid wax (Hi-Glass liquid wax glaze, GeorgeTaub Products and Fusion Co., Inc., Jersey City, N.J .)before investing and casting. There is little need foran opposing cast because the coping has all the details o fthe previous cast crown or tooth before preparation;but an opposing model can be used to verify occlusalrelationships.

11. Cast, polish, and finish the casting. At the try-instage, the margins and the occlusion are secured. Finally,

adaptation of the RPD to the new crown is appraised(Fig. 9). Cement the crown when all necessary adjust-ments have been made.SUMMARY

A procedure to restore an abutment tooth with acomplete cast crown to fit an existing RPD has beendescribed.REFERENCES

Teppo, K. W.: A technique for restoring abutments for remov-able partial dentures. J PROSTHET DENT 40~398, 1978.Gavelis, J. R.: Fabricating crowns to fit clasp-bearing abutmentteeth. J PRCXTHET DENT 46~673, 1981.Jordan, R. D., Turner, K. A., and Taylor, T. D.: Multiplecrowns fabricated for an existing removable partial denture. JPROSTHET DENT 48~102, 1982.Schneider, R. L.: Adapting ceramometal restoration to existingremovable partial dentures. J PROSTHET DENT 49:279, 1983

Re,tmnt reyuests to.DR. KHOSRGW SIG.ARCWIII1152 BARROILHET AVE.HILLSBORO, CA 94010

Endodontically treated teeth as abutmentsJohn A. Sorensen, D.M.D.,* and James T. Martinoff, M.D., Ph.D.**University of California, School of Dentistry, and University of Southern California. School of Medicine andPharmacy, Los Angeles, Calif.

T e literature on endodontically treated teeth as abut-ments for fixed and removable partial dentures is sparse.Reports have been primarily empirical statementsbecause limited clinical studies have been performed.

Some authors# suggest caution with the use of apulpless tooth as an abutment for a removable partialdenture (RPD) especially when it is a rotation point foran extension RPD. Others propose that any endodonti-tally treated tooth can be used as an abutment. It hasgenerally been thought that pulpless teeth require adowel to reinforce the tooth against fracture.2-5 However,our own previous research demonstrated that there was

Presented at the American Prosthodontic Society, Newport Beach,Calif., and the Pacific Coast Society of Prosthodontists, SantaBarbara, Calif.*Assistant Professor, Sections of Removable Prosthodontics and Post-graduate Fixed Prosthodontics.**Director of Education.

tKratochvi1, F. J.: Personal communication, 1982.SKrol, A. J.: Personal communication, 1982.THE JOURNAL OF PROSTHETIC DENTISTRY

no appreciable improvement in clinical success ate withdowel placement for endodontically treated teeths6Sever-al in vitro studies report similar conclusions.- Further-more, we reported that pulpless teeth with a traditionalcustom-tapered cast dowel and core failed more fre-quently than pulpless teeth without intracoronal rein-forcement. Conversely, parallel-sided serrated posts sig-nificantly improved the longevity of endodonticallytreated teeth.The present clinical investigation compared 1273endodontically treated teeth as abutments for crowns orprimary support for fixed and removable partial den-tures. Various methods of intracoronal reinforcement forabutments were examined for the rate and manner offailure.LITERATURE REVIEW

Numerous articles discussing a variety of factors inabutment selection appear in the literature.4a 5, -3 How-ever, little information is available to evaluate endodon-tically treated teeth as abutments for fixed partial

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SORENSEN AND MARTINW$

Table I. Comparison of success and failure rate of abutment teeth_____No crown Crown FPD RPD

No. % No. % No. c/o No. /$Success 160 75.8Failure 51 24.2Total 211 16.6

Crown vs. FPD x1 = 5.26; p < .05Crown vs. RPD x2 = 23.1; p < ,001FPD vs. RPD x2 = 3.48; ns

833 94.8 116 89.2 41 7.446 5.2 1-I 10.8 IL ZL.i-879 69.0 130 10.2 5; 42

-

dentures (FPD) or RPDs. Many authors feel thatreinforcement with a dowel is mandatory if these teethare to be used as FPD or RPD abutments.3-9 It is feltthat pulpless teeth must be adequately reinforced if theyare to be subjected to the demands of greater stresses asabutments.3-

No citations could be found in the literature regardingspecific considerations in the use of endodonticallytreated teeth as abutments for RPDs. Kratochvil* cir-cumvents endodontically treated teeth as abutments forRPDs, especially when the tooth serves as a distal-extension partial denture abutment. Krolt concurs withthis philosophy if the tooth was endodontically treatedmore than 10 years earlier.

In evaluating partial denture abutments and theresultant forces, it is necessary to differentiate betweenentirely tooth-borne and combination tooth-tissue-bornepartial dentures.2n~2Krolz2 states: In the fully toothborne partial denture occlusal stresses are transmitted tobone by way of the periodontal ligament. It functionssimilarly to a fixed partial denture. The extension basepartial denture, however, derives its support from twodifferent tissues, teeth and edentulous ridge each havingdifferent degrees of displaceability. This often results intorquing stress on abutment teeth.Teeth that serve as FPD abutments bear greaterstresses in function than single crown abutments.-Studies have demonstrated that teeth serving as abut-ments for RPDs receive greater stresses n function thannonabutment teeth.23-26 istal-extension partial dentureabutment teeth withstand greater stresses han any otherabutment tooth.~2.2,27-33 hese stresses can fractureteeth weakened by endodontic therapy and dowel spacepreparation.There is a dearth of research comparing the stresseson endodontically treated teeth that serve as abutmentsfor crowns, FPDs, or RPDs. Although assumptions havebeen made, there is no indication for greater reinforce-ment of pulpless teeth that act as FPD or RPDabutments.

Nayyar et a1.34eported that amalgam coronal-radicu-*Kratochvil, F. J.: Personal communication, 1982.tKrol. A. J.: Personal communication, 1982.632

lar cores can be used to restore abutments for FPDs andRPDs. Other investigators suggest that a composite resincore or amalgam core with a prefabricated post isacceptable for single restorations but a cast dowel andcore is necessary for abutments.4-x

Chan and Bryant 35 found that cast gold dowel andcores required less force before failure occurred, withteeth showing evidence of root fracture. The prefabri-cated post in combination with amalgam or compositeresin exhibited fracture of cores but less evidence ofdislodgment or root fracture. These results were inagreement with two other studies.73Perel and Muroff proposed that additional canalsmust be enlisted to fabricate a multiposted post and corefor posterior abutments.In a longitudinal study of combined periodontal andprosthetic treatment, Nyman and Lindhej evaluated299 individuals for 5 to 8 years. Of the 332 fixed partialdentures fabricated for the patients, 75% of the abutmentteeth that fractured were endodontically treated withposts and were serving as terminal abutments.

Langer et al.38 evaluated 100 patients 10 years afterroot resections were performed. A total of 47.4% failedby root fracture, commonly in mandibular molars. Theteeth frequently had weakened lateral walls of the rootdue to endodontic instrumentation and/or post spacepreparation with questionable post design. In mostinstances, the breakdown did not become evident until 5to 10 years after resection. They recommended that onlyteeth with large roots and large clinical crowns should beused and tipped or isolated mandibular teeth should not.be routinely selected for terminal abutments of FPDs.

In summary, empirical statements regarding the useof endodontically treated teeth as abutments for FPDsand RPDs have been made. Conflicting reports in theliterature have disconcerted dentists as to the type ofcoronal-radicular stabilization necessary for the pulplessabutment tooth.METHODS

Over 6000 patient records of nine general practition-ers were reviewed, and teeth with endodontic therapywere selected. Treatment performed for patients wasverified radiographically, and teeth were not included in

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ENDODONTICALLY TREATED ABUTMENTS

the study if they were endodontically treated less than 1year previously. Endodontically treated teeth that faileddue to periodontal pathosis or carious involvement werealso excluded. Based on these delimitations, 1273 teethendodontically treated 1 to 25 years prior to the studywere reviewed. Data were collected for independentvariables listed below.Type of abutment

Endodontically treated teeth were divided according tothe type of abutment: (1) no crown, single tooth; (2)single crown; (3) fixed partial denture abutment; and (4)removable partial denture abutment. In categories two,three, and four, the types of acceptable retainers includedthree-quarter, seven-eighths, full gold, mesial-occ lusal-distal onlay, and ceramometal crowns.Intracoronal reinforcement

Teeth without intracoronal re inforcement includedpin amalgam s, pin composite resin fillings, and tempo-rary fillings. Teeth with intracoronal reinforcementwere divided into the following categories: (1) taperedcast dowel and core, (2) cast Para-Post and core (Whal-edent International, New York, N.Y.) and (3) Para-Postand amalgam or composite resin core.Manner of failure

Failures of endodontically treated teeth were differen-tiated into two groups. Group No. 1 teeth were consid-ered restorable because of dislodgment or tooth fracture,and group No. 2 teeth were considered nonrestorablenecessitating extraction due to tooth fracture, verticalroot fracture, or root perforation.

The records were reviewed for information subse-quent to endodontic therapy and the last recordedexamination. The definition of clinical successwas basedon the dentists last examination.RESULTS

Table I presents a comparison of the success andfailure rates of abutment teeth. The data indicate thatthe greatest failure rate (24 .2%) was associated withpulpless teeth without a crown. A comparison indicatedthat the failure rate of RPDs (22.6%) was twice that ofFPDs (10.2%) and four times that of teeth with crowns(5.2%). Statistical analysis (chi square) revealed that thesuccess ate of crowns was significantly higher than thatof RPDs (p < .OOl) and FPDs QJ < .05). Althoughthere was a difference in the success rate of FPDs andRPDs, chi square analysis did not indicate a statisticallysignificant difference between the two types of abut-ments.

Table II compares the effects of intracoronal rein-forcement on the success and failure rates of abutmentteeth. The presence of intracoronal reinforcement did

not appreciably influence the success rate of teethwithout coronal coverage (no post, 75.4%; post, 87.5%).In single teeth with coronal coverage, the presence ofintracoronal reinforcement decreased the success ate (nopost, 96.7%; post, 87.5%) and was statistically significant(p < .Ol). Intracoronal reinforcement had a limitedeffect on the success rate of FPD abutments; however,RPD abutments demonstrated a significant improve-ment with intracoronal reinforcement (p < .Ol).Table III presents data associated with success andfailure of abutment teeth with differen t intracoronalreinforcement. Unfortunately, the sample size of thisanalysis was small; therefore, no statistical comparisonswere made. However, trend analysis suggested that thecast Para-Post and the Para-Post and amalgam orcomposite resin core were more effective methods ofintracoronai reinforcement than the tapered cast doweland core. The failure rate of the tapered cast dowel andcore ranged from 12.1% for abutment teeth with crownsto 13.3% for RPDs and 16.7% for FPDs. The failurerate of the cast Para-Post was 0% for single crowns andRPDs, but FPDs were not restored with cast Para-Posts. The failure rate of the Para-Post and amalgam orcomposite resin core ranged from 2.7% for crowns to 0%for FPDs and RPDs.

Table IV presents a comparison of the manner offailure with the type of abutment tooth, but the samplesize was too small for statistical comparison. However,trend analysis suggests a relationship between restorableand nonrestorable tooth fracture and the type of abut-ment. The percent of restorable tooth fractures for RPDs(13.2%) was twice that of the FPDs (6.2%) and seventimes that of the single crowns (1.8%). Similar resultswere obtained for nonrestorable tooth fractures thatrequired extraction. The rate of nonrestorable too thfracture for RPDs (7.5%) was twice that of the FPDs(3.1%) and eight times that of the crowns (0.9%). Theresults were less dramatic for vertical root fracture thatrequired extraction. The rate for RPDs (1.9%) wastwice that of the FPDs (0.8%) and three times that of thecrowns (0.6%).DISCUSSION

The findings from this study suggest reevaluation oftraditional guidelines for a more flexible approach to aspecific situation. The divergence of treatment for pulp-less teeth reflects the lack of evidence to substantiate theguidelines. Consider the following two assumptions thathave been empirically supported.Assumption No. 1

Dowel reinforcement is mandatory in every endo-dontically treated tooth, especially FPD and RPDabutments. Contrary to the belief that dowel placementis mandatory in all pulpless FPD and RPD abut-

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Table II. Comparison of success and failure rate of abutment teeth with and without intracoronalreinforcement -.----

Type of abutment- -__---...-- --__-..-... ..__ -.- .._.. _.No crown Crown-._______ ----__

Success Failure Total Success Failure Total-___- .___.-No. % No. % No. % No. % No. iri7 No. %,

No post 153 75.4 50 24.6 203 96.2 520 96.7 JR 33 538 61.2Post 7 87.5 1 12.5 8 3.8 313 91.8 28 g? s 341 38.XTotals 211 16.6 879 69.0Chi square analysis x2 = 0.13 XT = 9.0!Significance NS p < .Ol

Table III. Comparison of success and failure rate of abutment teeth with different methods ofintracoronal reinforcement*

Crown FPD RPDI____ --___-~ -..Type of Success Failure Success Failure Success Failure___-- -.-_..-_

reinforcement No. % No. % No. % No. % No. % No. 5,Tapered cast dowel and 174 87.9 24 12.1 25 83.3 5 16.7 13 86.7 2 13.3coreCast Para-Post 28 100 0 0 0 0 0 0 IO 100 0 0Para-Post and amalgam 109 97.3 3 2.7 10 100 0 0 5 100 0 0

or composite resin -.--~-_--.--...~.--.__ _*Chi square analysis was not performed because sample six was LOO mall for certain cells in tabk

ments,3-9 dowel placement demonstrated variableeffects on the success ate of abutment teeth. Statisticallysignificant improvement in success ate was not recordedwith the placement of a dowel in FPD abutments. Inpulpless RPD abutments, dowel placement significantlyincreased the success rate from 56.5% to 93 .3%. Thisfinding may illustrate the difference in functional forcesplaced on various abutment teeth. Perhaps the FPDretainer behaves similarly to a single crown while theRPD abutment is subjected to many m ore tensional andtorque forces from the RPD.Hoag and Dwyers in vitro study tested single crownson posterior teeth. They reached a similar conclusionwhen an interlocking stock and cast gold post and core inconjunction with a full crown actually decreased thepoint of failure.Similarly, Gelfand et a1.39ound that when full crownswere placed, there was not a difference in failure load ofmolars regardless of the type of coronal-radicular stabi-lization.Assumption No. 2

A cast dowel and core is the restoration of choice forendodontically treated abutment teeth.+* In compar-ing different intracoronal reinforcements, the sampiesize was small and could not be substantiated bystatistical tests. However, trend analysis suggested thatthe tapered cast dowel and core is not necessarily the best634

treatment. The data indicate that the failure rate of castPara-Posts and Para-Post and amalgam or compositeresin core were considerably lower than the cast doweland core. Our previous study found that the tapered eastdowel and core had a higher failure rate than teeth withno dowel.In vitro studies have demonstrated that the taperedcast dowel and core caused more irreversible damagenecessitating extraction than did other dowel tech-niques.7,3'~36 These in vitro findings are supported by ourearlier research.

The data from Tables II and III suggest that anondowel technique such as an amalgam coronal-radicular core would suffice for single crowns and FPDabutments;34 but placement of a dowel and som e type ofcore for retention is necessary for the success of a RPDabutment.As discussed in a previous article, the manner offailure of a dowel system should be considered whenselecting a method of restoration. In this study,. themanner of failure was correlated with the type ofabutment. As expected from the literature,~~1~2~ .?7-Ytrends in the data from Table IV suggest that as oneproceeds from a single crown to an FPD and to an RPDthere is a concomittant increase in the stressesof functionto which the teeth are submitted. This may be inter-preted from the trend in the data in which FPDs hadthree times the rate of restorable and nonrestorable tooth

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ENDODONTICALLY TREATED ABUTMENTS

SuccessNo. %

Type of abutmentFPD RPD

Failure Total Success Failure Total Grand totalNo. % No. % No. % No. % No. % No. %

80 89.9 9 10.1 89 68.5 13 56.5 10 43.5 23 43.4 853 67.036 87.8 5 12.2 41 31.5 28 93.3 2 6.7 30 56.6 420 33.0130 10.2 53 4.2 1273

x2 = 0.01 x2 = 8.11NS p < .Ol

Table IV. Comparison of type of failure with type of abutment

Type of failureNo crown

No. %Crown FPD RPD

No. % No. % No. %Dislodgement (restorable)Tooth fracture (restorable)Tooth fracture (extraction)Vertical fracture (extraction)Iatrogenic perforation (extraction)No failure

- - 14 1.6 1 0.8 -29 13.7 16 1.8 8 6.2 7 13.212 5.7 8 0.9 4 3.1 4 7.510 4.7 5 0.6 1 0.8 1 1.9- - 3 0.3 - - - -

160 75.8 833 94.8 116 89.2 41 77.4

fracture than single crowns, and RPDs had seven toeight times that rate. Similarly, the vertical root fracturerate for FPDs was twice that of crowns, and that ofRPDs was three times that of crowns.Studies from the periodontal literature3,* report highfailure rates associated with abutment teeth that wereendodontically treated and prepared for dowels, whichcorroborates the trends observed in the present study.

The success rate of all endodontically treated RPDabutments was 77.4% compared with FPDs (89.2%) andsingle crowns (94.8%). These findings support Kratoch-viis* practice of avoiding or circumventing pulplessteeth for RPD abutments, especially with distal-exten-sion RPDs.

that confers strength to an endodontically treated tooth ismore crucial than the placement o f a dowe1.6~8~0.40-42Preservation of tooth structure is even more importantwith pulpless FPD and RPD abutment teeth, whichrequire greater strength than single teeth.In determining the particular mode of treatment,endodontically treated teeth should be considered indi-vidually because one technique will not be applicable toall situations. Factors such as (1) the amount of remain-ing tooth structure, (2) arch position, (3) the type ofabutment, and (4) the functional loads applied should beconsidered.

Since this study did not take into account certainvariables in RPD and FPD design and fabrication,additional research is necessary. Variables that were notrecorded and may have affected that function of the RPDand stresses on the endodontically treated tooth include(1) rest and retainer design, (2) physiologic adjustmentof the RPD framework, (3) the quality of the adaptationof the extension bases, and (4) occlusion. In addition, thelength of the span of the FPD was not recorded, and nodistinction was made between tooth-borne and distal-extension RPDs. This data can offer further insight intothe interaction between functional forces and failure ofpulpless abutments.

Trend analysis suggests the following:1. The cast Para-Post and core and the Para-Post and

amalgam or composite resin core were more effec-tive methods of intracoronal reinforcement for abut-ment teeth than was the tapered cast dowel and core(Table III).2. The manner of failure was associated with the typeof abutment (Table IV).CONCLUSIONS

Evaluation of 1273 endodontically treated teethresulted in the following conclusions, based on statisti-cally significant findings.

Studies have shown that the remaining tooth structure*Kratochvil, F. J.: Personal communication, 1982.

1. Abutments for FPDs and RPDs that were endo-dontically treated had significantly higher failure ratesthan single crowns (Table I).2. Coronal-radicular stabilization had a variableaffect on abutment teeth. Dowel placement was associ-

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ated with a significantly decreased success rate in singlecrowns. Dowel placement had limited influence on thesuccess ate of FPD abutment teeth. Dowel placement isassociated with a significantly higher success rate inRPD abutment teeth (Table II).

We gratefully acknowledge the assistance of Ms. E.V. Philo in thepreparation of these three manuscripts.REFERENCES

I

234

5

6

78

9.IO.11.

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I4IS16

I7IX

I920

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Henderson. I)., and StePfel, V. L.: McCrackens RemovablePartial Prosthodontics, ed 5. St. Louis, 1977, The C. V. Mosb)co., p 215.Inglc, J. I., and Bevridge, E. E.: Endodontics, ed 2. Philadelphia,1976, Lea & Febiger, pp 778-779.Kornfeld, M.: Mouth Rehabilitation, ed 2. St. Louis, 1974. The(1. V. Mosby Co., p 631.Tylman, S. D.: Theory and Practice of Crown and Bridge FixedPartial Prosthodontics, ed 6. St. Louis, 1970, The C. V. MoshyEo nston, J. F., Phillips, R. W.. and Dykema, R. W.: ModernPractice in Crown and Bridge Prosthodontics, ed 3. Philadelphia,1971, W. B. Saunders Co., p 608.Sorensen, ,J. A., and MartinofT, J. T.: Intracoronal reinforcementand coronal coverage: A study of endodontically treated teeth. JPROS.THE DENT 51:780, 1984.Lovdahl, P. E.. and Nicholls, J. I.: Pin-retained amalgam coresvs. cast-gold dowel cores. J PR~STHET DENT 38~507. 1977.Guzy, C;. E., and Nicholls, J. I.: In vitro comparison of intactendodontically treated teeth with and without Endo-Post rein-forcement. J PR~STHET DENT 42:39, 1979.Hoag, E. P., and Dwyrr, T. G.: A comparative evaluation of thepost and core techniques. J PR~STHET DENT 47:177, 1982.Sorensen, J. A.. and Martinoff, J. T.: Clinically significantfactors in dowel design. J PROSTHET DENT .X:28, 1984.Shillingburg, H. T., Hobo, S., and Whitsett, L. D.: Fundamen-tals of Fixed Prosthodontics. Berlin, 1976, Quintessence Books,pp 17-28.Reynolds, J. M.: Abutment selection for fixed prosthodontirs. JPROSTHET DENT 19:483, 1968.h4oulton, P.: Selection of Abutment Teeth: Clinical Dentistry.Hagerstown, Md., 1979. Harper and Row Publishers, chap33.(Zolman, H. L,.. Restoration of endodontically treated teeth. DentClin North Am 23~647, 1979.Lorey, R. E.: Abutment considerations. Dent Clin North Am24:63, 1980Sapone, J., and Lorencki, S. F.: An endodontic-prosthodonticapproach to internal tooth reinforcement. J PR~STHET DENT45:164. 1981.Lau, 1. hl. S.: The reinforcement of endodontically treated teeth.Dent Clin North Am 20~313, 1976.Kantor, M. E., and Pines, M. S.: A comparative study ofrestorative trchniqueq for pulpless teeth. J PROSTHET DENT38:405, 1377Perel. M L., and Muroll, F. I.: Clinical criteria for posts andcores. J PKOSIHET DENT 28:405, 1972.Kratochvil, F. .J.: InfIuence of occlusal rest position and claspdesign on movement of abutment teeth. J PROSTHET DENT13:114, 1963Krol, A. J.: Clasp design for extension-base removable partialdentures. J PROSTHET DENT 29:408, 1973.

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ally treated teeth as abutments

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