Acid-Etched, Resin BondedCast Metal Prostheses:

A Retrospective Study of 5-to 15-Year-Old Restorations

Keith E. Thayer, DOS, MS'

Vincent D. Williams, DOS, MS"

Ana M. Diai-Arnold, DDS, M S ' "

Daniel B. Boyer, DOS, MS, PhD"*

College of DentistryUniversity of IowaIowa City, Iowa 52242

Eighty-five resin bonded prostheses were evaluated in aretrospective study over a 15-year period. All had been infunction for at least 4.5 years. Multifactorial variables werestudied to ascertain their effect on debonding and the healthof the oral tissues. The results showed; (1) the caries rate ofthe retainer teeth was 6%, (2) the mean gingival indices for theprostheses were significantly higher {P > .0001) than those ofthe remaining dentition, (3) 61% of the restorations had notdebonded (if failure resulfing from trauma was not included,the incidence of debonding dropped to 19%], and (4) allpatients liked their prosfheses. InlI Prosthodont 1993;6:264-269.

T his study is the third in a series of retrospectivestudies conducted by these investigators on

resin bonded prostheses and reports observationsat the 15th year. A 7-year study' followed by a 10-year study- were previously completed. This studycomprised 85 resin bonded prostheses, of which 23had been examined and evaluated in all three stud-ies, 43 had been examined in the 10- and 15-yearstudies, and 19 were first evaluated in tbe 15-yearstudy. Numerous articles bave been written on thistype of fixed restoration,=-'^ but few have evaluatedlong-term clinical performance. The purpose ofthis study was to evaluate the efficacy of the resinbonded prostheses in the sample population andrecord the complications attending this treatment.

'Professor, Department of Prosthodontics."Professor, Department of Family Dentistry.

'"Associate Professor, Department of Family Dentistry.""Professor, Department of Operative Dentistry.

Reprint requests: Or Thayer.

Presented at the lADR 69th General SessionlAADH 20th AnnualSession, 18 April, 1991, Acaputco, Mexico.

Materials and Methods

Figbty-five anterior and posterior resin bondedprostbeses of both etched metal and perforateddesign were evaluated. All restorations were origi-nally placed between 1975 and 198.5 and had been inservice for at least 4.5 years. Of the 85 prostheses,53 had been placed for female and 32 for malepatients. Dental students made46oftheprosthesesand 39 were made by faculty or residents. Sixty-fourpercent of the prostbeses were placed in patientsunder 50 years of age. The age distribution of theprostheses is sbown in Table 1.

Three dentists completed the clinical examina-tions using the same criteria that were used in the10-year retrospective study.- A mouth mirror, ex-plorer, and periodontal probe were used in theexamination. Irreversible hydrocolloid impressionsfor casts and 35-mm slides were made for allpatients.

Tbe 35-mm slides were studied for proper es-thetic concerns such as condition of the edentu-lous ridge, pontic shade, and incisal bluing. Incisalbluing is a term that is used to describe colorcbange of tbe retainer tooth due to metal showingthrough a translucent incisal third of the crown.

The International lourral of Prosihodoniics 2 6 4 Volume 6, N i ; - " - -

Thaye Acid.Etched, Resin Bonded Cast Melal Proslfieses

Figs la and Ib Six-unit mandibular prosthesis with perforated retention, no caries, gingivitis, prosthesis Gi ^ 1.0, piaque present onthe iinguai surfaces of ail retainers, and resin tiash tound on three retainers. The unit was reiuted twice, had a slight washout olpertorations, no incisai bluing, and the retainers and pontics were in occlusion in both centric and eccentric excursions.

Table 1 Age Distribution of the Prostheses Groupedby Year

Age (yl

4 - 55 - 66 - 77 -88 -99-10

10-1111-1212-1313-14

N

10211712

638413

Percent

11.324.720.014,1

7.13.59,44,71,23,5

Cumuiativepercent

11.836.556,570.677 681.290.695,396,5

100.0

Mean age ol prosthesis = 7.3 years.

This is caused by eitber using a nonopaquing iutingcement or microleakage of tbe perforated retainercausing a dark oxide layer on the internal surface ofthe retainer casting,

Periodontai healtb was determined by evaluatingthe general gingival index as described by Loe andSilness'" as well as tbe gingival index of retainerfeeth. Tissue color, edematous conditions, andhealth of tbe edentulous tissue in the pontic areawere recorded. Probing deptbs were recorded asspecified in tbe general gingival index determina-tion system. Tbe probing depths, plaque, and resinflash on all retainer teeth were recorded as well.

Retainer design was described relative fo surfacearea, retention metbod (etched metal or perfo-rated), circumference of posterior retainers in de-grees, and number of occiusai rests. Retainer di-mensions were measured witb a periodontal probemesiodistally and occlusogingivally or inciso-gingivally and tbe numbers multiplied to estimatethe surface area. In Rocbette design restorations.

thenumberandsizeof perforafionsin tbe retainerswere recorded. Perforations were evaluated for dis-solution of the luting material. The marginal integ-rity of tbe retainers was also evaluated. All retainerswere evaluated for debonding using finger pres-sure and an explorer. Pontic design was recorded aseither conical, ridge lap, nonconfacting, or com-plete ridge lap. Occlusion for each restoration wasevaluated by recording centric and eccentric con-tacts of pontics and retainers during mandibularmovement.

In the absence of the examining dentist, eacbpatient was asked: HI how they liked the restora-tion; {2) if there were any problems with cleaning;(3) if they were happy with tbe esthetics; and (4) ifthere were any other problems witb the prosthesis.

Distribution of pontics and retainers was such that74% of tbe restorations had two retainers, 78% badone pontic, 5% had three retainers, 16% had fourretainers, and 1% had six retainers; 18 of the restora-tions had two pontics and 1 bad four. The prosthesiswith four pontics was placed on a 74-year-oldwoman and bad been in service for 7 years and 8months. The restoration with six retainers was on a50-year-old woman. The patient had completedadult orthodontics and had one pontic in an ortho-donticaliy created space witb the mandibular ante-rior teeth splinted from canine fo canine as a fixedorthodontic retainer. The restoration had been inservice for 13 years and 1 month (Figs la and Ib),

Fifty-five of the restorations were placed in theanterior region, while 11 were posterior restora-tions; 19 had both anterior and posterior retainersand/or pontics. Only one of the posterior restora-tions was placed before 1980. The other 10 wereplaced between January 1980 and January 1984,Thirty of fhe restorations were placed in the mandi-ble and 55 were placed in the maxillae.

í6 . Numbers, 1993 263 lournai oí Prosthodonlic

Acid-Etthed, Resm Bonded Casi Mêlai Prosthe Thayer cl al

Figs 2a and 2b Tbree-unif maxillary anterior prostbesis witb perforated refention. Tbis unit bas been in function for 13.3 years and wasreluted atter 6.5 years. Ttie prostbesis Gl = 2.5 with no probing deptbs > 3 mm. There was gingivitis; however, no canes was found.There was sligbt wasbout ot the resin composite in tbe perforations and slight mesial bluing or disooloration in the mcisal tbird ol thecrowns. Tbe restoration was in occlusion in both centric and eccentric excursions.

Prostheses Materials and Design

The classification affecting debonding variableswas submitted to the statistical tests of ANOVA, chi-square, and Fisher's exact test. Student's í test wasused to determine the variables affecting debond-ing (mean number of perforations, mean area ofretainers, mean probing depth, mean age of pa-tients, and mean age when first bonded).

Forty of the restorations were of the perforateddesign and 41 of the etched metal design. Theremaining four prostheses had previously de-bonded and perforations had been made in themetal prior to rebonding.

Seven different luting agents had been used withthese restorations: 53% were luted with Comspan(LD Caulk Co, Milford, DF); 19% with Adaptic (John-son and Johnson, Fast Windsor, NJ); 17% with Con-clude (.ÍM Dental Products Div, St Paul, MN); and 7%with Concise (3M). Simulate (Kerr Mfg, Romulus,Ml), Caulk Exp (LD Caulk), and Kerr (Kerr Mfg) resinbonded prosthesis cements were each used withone patient. There was no record of the lype ofluting agents used on 11 of the 85 restorations-

Various alloys were used in the fabrication of therestorations; 19 were of Biobond (Dentsply, York,PA); 6 were of Cameo (Jelenko Dental HealthProducts, Armonk, NY); and 7 were of Kexillium ill(Jeneric Cold Co, Wallingford, CT). Unknown non-precious metals accounted for 44 of the restora-tions and the metal for9was unknown. The restora-tions were fabricated by various commercial dentallaboratories.

The majority of the perforated design prostheses(25 of 44) had a hole size diameter of a no. 2 roundbur, 12 had a hole size of a no. 1/2 bur, 6 were of ano, 1 bur size, and 1 was no. 4 bur size.

A ridge lap or modified ridge lap pontic designwas used for 71 of the restorations; ti pontics wereconical and 1 was a complete ridge lap.

Results

Harti Tissue Findings

Hard tissue examinations showed a very low inci-dence of caries, as in Figs 2a and 2b; 84% of theprostheses were caries free, 9% had one lesion, and7% had two to four lesions. There were only fiveretainer teeth (6%) with carious lesions, some ofwhich were decalcified enamei or white spot le-sions. Two of the patients exhibited generalizedcaries with a total of 14 lesions identified. As re-ported in the two previous studies,'- caries con-tinues to appear to be a minor problem.

The incidence of resin flash continues to remain

Table 2 Gingival Index*

Area

Oral CavityResin tDonded

prosthesisConventional

prosthesis

Oral CavityResin bonded

prostbesisConventional

prostbesis

N

9999

7

8585

7

Mean SD

10-year study

0,90.7

0.9

0.50.5

0.4

15-year study

0.30.6

1.3

0.30.5

0.6

Range

O-2.00-2.2

0.5-1.4

0-0-80-2.5

0.5-2.0

The Internalional lojrnai of Prosthodonti< 266

Thayer et al Acid-Etched, Resin Bonded Casi Melal Prostheses

Table 3 Literature Review of Debonds of Resin Bonded Prostheses

AuthorsObservationperiod (mo)

No,prostheses

No,debonded

Kuike 8 Drennon*Den eh y 8 Howe'Shaw 8 Tay'Berge ndai et aPEshleman et al=Ekstrand'Williams et al=Thompson & Wood'"Tanaka et ai'Van der Veen et al"Priest & Donate II i "Williams et al=Creugers et a l "Olin et a l "

•RetainersfTrauma not included.

19771979198219831984198419841986198619871988198919901990

2436445936368441361223

1206084

203046

10039

12063

180-230645890

20396

239

296

2210-6

101020t4711

20102029151816223

15617,2202211

somewhat high, with 32% of the restorations exhib-iting excess resin at the gingival margins. This find-ing suggests that all clinicians should carefully exam-ine gingival margins for resin flash, as it blends inexceedingly well with tooth and root structure.However, of M surfaces with resin flash on 26 pros-theses, only four surfaces on four prostheses exhib-ited crevicular probing depths greater than 3 mm.

Soft Tissue Findings

The clinical record showed that 69% of the pa-tients had an initial periodontal problem (gingivitisorperiodontitis),asin Figs2aand2b, Thirty percentof the prostheses had crevicular depths greaterthan 3 mm as measured by the periodontal probe.However, of 808 probing depths evaluated on re-tainer teeth, only 63 recordings were greater than 3mm. The greatest probing depth recorded was 9mm. Plaque continues to be a problem in fixedpartial dentures, as 73% of the retainer teeth hadplaque on one or more surfaces. The residual ridgewas healthy in 90% of the prostheses studied. Noattempt was made to correlate pontic design withtissue health of the residual ridge except to recordthe area as either healthy or inflamed. Only onepatient had a complete ridge lap pontic, and thisarea was evaluated as inflamed.

Table 2 presents a comparison of the mean gingi-val indices (GIs]* of the oral cavities, retainers ofresin bonded prostheses, and conventional pros-theses of both the 10- and 15-year studies. Themean CIs of the resin bonded prostheses and theconventional prostheses were significantly higherthan the mean Ci of the oral cavities in the 15-yearstudy (paired í test, P = ,0001).

Table 4 Age of Prostheses When First Debonded

Age (y]

0-11-22-33-44-55-66-77 - 88 - 99-10>10

% a t7-year study

50100

2010100

---

-

% a t10-year study

33291299090Q00

% a t15-year study

309

156

12663363

Debonding

Debonding occurred in a total of 33 restorations(39%), with 3 restorations (4%) debonding as aresult of trauma. Only 16% had to be remade overa 15-year period; 4 because of porcelain fracture(5%) and 9 because of other causes (11%) includingmetal failure. If the prostheses that were remade ordebonded following trauma are eliminated fromthe data, the debond rate is 19%, similar to thatreported in the literature (Table 3). There was nosignificant difference (P - ,394) in debond ratesfor etched vs perforated retainer designs adjustedforage.

The age of the prostheses when first debonded isshown for all three studies in Table 4, The mean ageof the restorations at debonding was 3,7 years forthose in the 15-year study (range 0.04 to 10.6 years).

The area of the retainer influenced debonding of

3,1993 267 The Inlernational Iournal ot Prosthodontics

Acid-Elched, Resin Bonded Cast Metal Prosthe Thayer et

Table 5 Comparison of Prostheses in 7-, 10-, and15-Year Studies (n = 23)

% at % at % atFindings 7-yearstudy 10-yearstudy 15-yearstudy

CariesPlaqueCrevicular depth

> 3 mmResin composite

wearBiuing

05717

44

4

Table 6 Number of Times Prosthesis was Reluted

No, ofprostheses

Timesreluted % of total

61.222.410.61.21.21.32.4

the prostheses. The mean area of the retainers thatdebonded (37.6 mm-¡ was significantly smaller |itest, P = ,0421] than that of retainers that did notdebond (44.9 mm'].

The number of perforations in Rochette pros-theses also affected debonding. The mean numberof holes in retainers that debonded (7.3) was signifi-cantly less than that of retainers that did not de-bond (9.0) (f test, P = .04%). Larger retainers had alarger number of holes, so this was probably whythe number of holes was associafed with less de-bonding. Marginal washout of the cement influ-enced debonding. Prostheses that debonded hadhigher degrees of marginal washout (chi-square,P = .032). The debonding resulting from the vari-able marginal washout was tested using chi-squareand Fisher's exact test (1 tail, 2 tail) and was found tobe significant (P = .05). The washout was measuredon the debonded prostheses, however, and mayonly indicate that the reluted prostheses did not fitas well as ones that had not been reluted. A pre-vious study- showed no significant difference (chi-square, P = .05] on the relationship of marginalwashout to debonding.

The gender of the patients was related to de-bonding of the prostheses. Debonding occurredmore frequently in men than in women (chi-square, P = .036]. Olin et al'= obtained similarresults. This result might be attributed to thestronger force of mastication in men."

Poor resistance form of prostheses (less than 180degrees in circumference) may have played a role indebonding. Seventy-five percent of the debonds ofperforated retainers occurred with seven restora-tions that were less than 180 degrees in circumfer-ence and 31 % occurred with 16 etched retainers thatwere less than 180 degrees in circumference. Of thelatter, three restorations needed to be remade.

The following variables did not significantly influ-ence debonding (chi-square, a = ,05); age of pa-tient, year of prosthesis attachment, prosthesislocation (anterior vs posterior], placement in maxil-lary vs mandibular arch, laboratory used, type of

metal, luting agent, number of retainers, numberof pontics, loss of resin composite in perforations,perforation size, nature of occlusion ¡centric oreccentric), initial periodontal problems, and prob-ing depths greater than 3 mm.

At the end of the 15-year study 61% of the pros-theses had not debonded and 22% had to be re-bonded only once. A comparison of the 23 restora-tions evaluated in the 7-, 10-, and 15-year studies isgiven in Table 5. It was found that there was anincrease in the incidence of plaque from 57% to87%, in resin composite wear from 44% to 74%, andin incisai bluing from 4% to 35%. Caries and prob-ing depths greater than 3 mm had a slight increasein incidence. Table 6 indicates the number of timesprostheses were reluted.

Subjective findings showed that 100% of patientsliked their restorations. However, 17% of the pa-tients expressed problems with oral hygiene, 37%expressed problems with shade or color, and8% had a fear of debonding of the fixed partialdenture.

Discussion

Hard tissue disease (caries) does not appear to bea problem with resin bonded prostheses. Threesuccessive studies by the same authors over a 15-year period (Table 5] show that the retainer teethhave a very low rate of caries even though theplaque occurrence and CI of the prostbeses arehigher than that of the oral cavity Cl (Table 2). Thismay result from resin banded prosthesis prepara-tions being in enamel, whereas conventional pros-theses are prepared in dentin. Also, the interfacebetween resin bonded prostheses is different thanconventional prostheses in that resin compositetags penetrate the enamel providing a microme-chanical retentive seal between the prosthesis andthe enamel. Conventional prostheses with dentinalpreparation must provide excellent retention, re-sistance form, and proper luting agents to preventcaries. However, this may be too simplistic a ration-

lojrnalof Piosthodontii 268 Volume 6, N

Thayer et al Acid-Eichcd, Resin Bonded Cast Metal Prostheses

ale when so many variables exist in the oral cavity, ie,patient oral hygiene compliance and procedures.

That resin bonded prostheses are tolerated wellby the periodontal tissues is shown by the fact thatprobing depths greater tban 3 mm increased only6% in the 7-, 10-, and 15-year studies (Table 5). Also,resin flasb occurred 32% of the time on tbe retain-ers but only four surfaces on four prostheses badprobing depths greater than 3 mm. Even though theCIs of resin bonded and conventional prostbeseswere significantly higher in the 15-year study com-pared to the 10-year study where no cbange wasnoticed (Table 2), it should be noted that the differ-ence in gingival indices was very small. This differ-ence could have resulted from interrater validity, asthree different operators conducted the study andmay have used different periodontal probing pres-sures. Even with the increase in plaque noticed inthe three successive studies (Table 5) and an inci-dence of resin flash of 32%, only 8% of retainerteeth had probing depths greater than 3 mm.

Proper design and tootb preparation affected de-bonding rates of resin bonded prostheses. Tbe areaof the retainer and tbe number of perforationssignificantly influenced debonding. Tbis is to beexpected, as a decreased surface area would haveless area for either mechanical or micromechanicalretention of the prostbesis. Marginal washout atthe margin interface with the enamel did affectdebonding. This may have resulted from rebondedprostheses being included in tbe study and tbepossibility of deforming the framework of a looseprosthesis during removal. Of tbe occurrences ofdebonding, 22% had to be rebonded only once(Table 6). There were debonds in 75% of the perfo-rated retainers and 31% of tbe etched retainerswhen tootb preparation and design called forencir-ciement of the tootb crown of less tban 180 de-grees. This would suggest that proper design andtooth preparation are essential for a successfulprognosis of the resin bonded prostbesis.

Summary

The results of this 15-year retrospective studycontinue to validate the results of the previousstudies.'- Caries on retainer teeth was very iow, theperiodontium did not show a greater incidence ofperiodontal disease, very few prostheses needed tobe remade, and the debond rate was acceptable.

The investigators continue to believe that theresin bonded cast prosthesis, when properly de-signed and placed in correctly selected patients, isan excellent restoration and may be the restorationof choice for a particular situation on a specificpatient.

Conclusions

This retrospective study reviewed 85 resin-retained prostheses 15 years after placement ofthese restorations. Based on the conditions of thestudy and the manner in which the evaluations weremade, the following conclusions may be drawn:1. The caries rate of resin bonded prostheses is

very low.2. Resin bonded prostheses do not contribute to

periodontal disease.3. Proper prosthesis design and tooth prepara-

tion do affect debonding rates of resin bondedprostheses.

References

1. Williams VD, Denehy CE, Thayer KE, Boyer DB. Acid-etchretainnd cast metal prostheses: A seven-year retrospectivestudy. ) Am Dent ASSQC 19e4;108:629-631.

2. Williams VD, Thayer KE, Denehy CE, Boyer DB. Casi metal,resin bonded prostheses: A 10-year retrospective study. |Prosthet Dent 1989;61 (4) :436-441.

5. Rochette AL. Attachmeni oí a splint to enamel of loweranterior leeth. J Proslhet Den( 1973;30:418-423.

4. KuhlkeKL, Drennon DG. An alternative to the anterior singletooth removable partial deniure. J Int Assoc Dent Child1977;8:11-14.

5. Denehy GE, Howe DF. A conservative approach lo the miss-ing anterior tooth. Quintessence Int 1979;7;23-29.

6. Shaw MJ, Tay WM. Clinical performance of resin-bondedcast metal bridges (Röchelte bridges!. Br Dent | 19B2;152:378-380

7. Bergendahl B, Hailonsten AL, Kock C, Ludvigsson M, OlgartK. Composite retained onlay bridges. Swed Dent | 1983;7:217-225.

8. Eshleman ]R, Moon PC, Barnes RF. Clinical evaluation of castmetal resin-bonded anterior fixed partial dentures. | Pros-lhet Dent 1984;51:761-764.

9. Ekslrand K. Erfarenheterav120 ko m po si I retine rade palaggs-broar. Tandlakartidningen 1984; 18:987-993.

10. Thompson VP, Wood M. Etched casting bonded retainerrecalls: Results at 3-5 years (abstract 12821. J Deni Res1986;65(specialissue):311.

11 Tanaka T, Fujiyama E, Shimizu H, Takaki A, Atsula M, Suriace

treatment of nonprecious alloys lor adhesior-lixed partialdentures. J Prosthet Dent 1986;55:455-462.

12. Van der Veen H, Bronsdijk B, van de Poel F. Clinical evalua-tion of resin bonded bridges with perforated retainer—Sixyear results. Quintessence Dent Tech 1987,11:5"(-56.

13. Priest GF, Donatelli HA. A four-year clinical evaluation ofresin bonded fixed partial dentures. | Prosthel Dent 1988;59(5): 542-546.

14. Creugers NHJ, Snoek PA, Van 'Thof MA, and Kayser AF.Clinical performance of resin-bonded bridges. a5-year pros-pective sludy. Pari III: Failure characteristics and survivalafter rebonding. | Oral Rehabil 1990;17:179-186.

15. Olin P, Hill EME, Donahue |L. Clinical evaluation of resin-bonded bridges: A retrospective sludy. Quintessence Inl1991; 22:873-877.

16. Loe H, Silness J. Periodontal disease in pregnancy. AciaOdontol Scand 1963;21:532-^551,

17. Okeson |. Fundamentals of Occlusion and Temporoman-dibular Disorders, e d l . SUouis: Mosby, 1985:46.

269 The International Journal ol Prosthodontic