Tanoue et al.

Int Chin J Dent 2006; 6: 53-59.

Survival of resin-bonded fixed partial dentures made from asilver-palladium-copper-gold alloy
Naomi Tanoue, DDS, PhD,a Takako Ide, DDS, PhD,b Koji Kawasaki, DDS, PhD,cKiyoshi Nagano, DT, PhD,d and Takuo Tanaka, DDS, PhDeab

Department of Specialized Dentistry, Nagasaki University Hospital of Medicine and Dentistry, Divisionof Fixed Prosthodontics and Oral Rehabilitation, Nagasaki University Graduate School of Biomedicalc
Sciences, Community Medical Network Center, Nagasaki University Hospital of Medicine anddDentistry, Dental Laboratory Center, Nagasaki University Hospital of Medicine and Dentistry,eNagasaki, and Department of Oral and Maxillofacial Rehabilitation, Kagoshima University Graduate
School of Medical and Dental Sciences, Kagoshima, Japan
Purpose: The purpose of this study was to evaluate the clinical performance of resin-bonded fixed partial
dentures (RBFPDs) made from a silver-palladium-copper-gold alloy.
Materials and Methods: The retention of 81 RBFPDs inserted during the 1987 to 2002 using a thione primer as
the metal conditioner (Metaltite or V-Primer) and an adhesive resin (Super-Bond C&B) was clinically evaluated.
Two levels of survival were defined: (1) complete survival (no debonding) and (2) functional survival (including
loss of retention on one occasion with rebonding of the original RBFPD). All data were obtained from clinicalexaminations, and missing data were censored at the date of the last available information. Mean survival
periods were determined using the Kaplan-Meier procedure.
Results: Of the 81 RBFPDs, five restorations failed, one of which could be rebonded. The observation durationand corresponding survival ratio for complete survival were 165 months and 43.9%, and those for functional
survival were 178 months and 87.7%, respectively.
Conclusion: The results indicate that Super-Bond resin combined with noble metal conditioners is a clinicallyreliable system for longevity of RBFPDs. (Int Chin J Dent 2006; 6: 53-59.)
Key Words: clinical evaluation, primer, resin-bonded fixed partial denture, thione.

Introduction
To conserve tooth structure, the minimal preparation required for resin-bonded fixed partial dentures(RBFPDs) is clinically advantageous because of there infrequently being damage caused after the loss. RBFPDs
bonded to enamel and dentin after minimal tooth preparation are an alternative to conventional fixed partial
dentures (FPDs) during replacement of missing teeth.1-5 Nevertheless, Dunne and Millar reported the highfailure rate of RBFPDs in comparison with conventional FPDs.6 RBFPD stability basically depends on theadhesive bonding of a resin-based luting agent to a metal framework, and on the bond strength between the
cement and tooth. However, RBFPD failure is reportedly influenced by various other factors such as toothpreparation resistance to displacement forces,7,8 preparation design,9-13 location,13-19 and the gender of thepatient.20 Due to these numerous influential factors, the prognosis and success rates of RBFPDs remain unclear.
The type of dental metal alloy selected for RBFPDs is also thought to be important for prognosis, since bondstrengths between the resin and the metal alloy are known to vary in accordance with alloy type.21 Hansson andBergstrom evaluated the longevity of RBFPDs and indicated that the bond strength between resin and high gold
alloys was too low to resist fatigue fractures.22 The type of resinous luting agent selected also has an effect on
RBFPD prognosis.23
A silver-palladium-copper-gold alloy is one type of metal alloy that can be used for RBFPDs.24,25 The
purpose of the present study was to collect long-term survival data of RBFPDs made from a silver-palladiumcopper-gold alloy inserted using a resinous agent under controlled clinical conditions by evaluation of theretention of the framework.

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Int Chin J Dent 2006; 6: 53-59.

Materials and Methods
Patients
One hundred and ten RBFPDs were inserted by three prosthodontic specialists at the Nagasaki University
Hospital of Dentistry (Nagasaki, Japan) in 99 patients between 1987 and 2002. The patients inserted with an
RBFPD had presented one or two missing teeth and two or three intact abutment teeth with good periodontal
support. All abutment teeth were caries-free or exhibited only minimal lesions that would not interfere withbonding. Enamel surfaces were suitable for etching and tooth alignment was acceptable. Attempts were madeto trace all patients for evaluation of bonding between RBFPD and teeth.
The inclusion criterion for participation in the study was the presence of stable occlusal relations. Although a
total of 79 patients were available for clinical reexaminations in our hospital, two were excluded from this study
because of unstable occlusal relations, while the other 20 could not be recalled. As a result, since all data were
to be obtained from just clinical examinations to avoid overlooking an RBFPD failure, a total of only 77 patients(43 female and 34 male) between 18 and 70 years old with 81 RBFPDs were evaluated. The distribution of
RBFPDs according to the age of the patients at the time of placement of the restoration is shown in Table 1. Of
the 81 RBFPDs, a total of 33 restorations were anterior and 48 posterior (anterior: 24 maxillary and 9
mandibular; posterior: 23 maxillary and 25 mandibular). Sixty-four restorations were performed for one missing
tooth and 17 for two. Fifty-nine restorations were cemented to two abutment teeth and 22 onto three.
Table 1.

Distribution of RBFPDs according to patient age at the time of placement.

Age (year-old)

<20

21-30

31-40

41-50

51-60

61-70

Number of RBFPDs
%

3
3.9

11
14.3

12
15.6

13
16.9

15
19.5

23
29.9

Clinical and laboratory protocol
Considering that splinting of abutments increases their resistance to the force on the teeth and the supporting
structure, Ante’s law27,28 and the principle of Duchange29 were adopted as clinical guidelines to determine thenumber and selection of abutments involved in the fabrication of the RBFPD in the current study. Tooth
preparation was carried out without a groove according to the method of Tanaka et al.26 All preparations had
supragingival finishing lines.
All RBFPDs were fabricated after a heavy-body/light-body impression (Exaflex or Exafine, G-C Corp., Tokyo,
Japan). The alloy used was a silver-palladium-copper-gold alloy (Castwell M.C. 12, G-C Corp.). This Castwell
alloy is categorized into an age-hardenable silver-based casting alloy consisting of 46% Ag, 20% Cu, 20%, Pd,
and 12% Au. According to the manufacturer, the alloy is applicable to inlays, single restorations, and fixed
partial dentures without porcelain fusing. For aesthetic purposes, pontics were veneered either with a hybrid
composite (Cesead II, Kuraray Medical Inc., Tokyo, Japan), or with a microfilled composite (Axis, G-C Corp.),since the alloy cannot be fused directly to ceramics. RBFPD framework fabrication was performed in the samelaboratory.
The inner surfaces to be bonded were airborne-particle abraded for 15 s with 50-70 µm alumina (Hi-Aluminas,
Shofu Inc., Kyoto, Japan) using an air-borne particle abrader (CL-FSG94, Heraeus Kulzer Inc., Armonk, NY,
USA), and primed with a noble metal alloy conditioner (Metaltite, Tokuyama Dental Corp., Tokyo, Japan; or54

Tanoue et al.

Int Chin J Dent 2006; 6: 53-59.

V-Primer, Sun Medical Co., Ltd., Moriyama, Japan).

Metaltite primer contains 6-methacryloyloxyhexyl

2-thiouracil-5-carboxylate (MTU-6) in ethanol, whereas V-Primer material contains 6-(4-vinylbenzyl-n-propyl)
amino-1,3,5-triazine-2,4-dithiol or -2,4-dithione tautomer (VTD) in acetone.

The V-Primer material is apioneering metal priming agent for noble alloys; hence, the material has been used for all of the FPDs with aservice period of 10 years or more. However, Metaltite material with improved bonding performance was later
released, and so the V-Primer material was replaced with Metaltite in the current study. Either primer can beused for seating conventional FPDs, although the luting agent should be limited to resin-based materials.
The enamel surfaces of the abutment teeth were polished with a brush and fluoride-free pumice, etched withan etching gel of 37-65% phosphoric acid for 30 s, and rinsed with water. The luting material used for the
RBFPDs was a tri-n-butylborane (TBB)-initiated self-curing resin (Super-Bond C&B, Sun Medical Co., Ltd.),
which contains methyl methacrylate (MMA), poly(methyl methacrylate) (PMMA), and 4-methacryloxyethyl
trimellitate anhydride (4-META) as the carboxylic functional monomer.
Restorations were inserted under relatively dry conditions using cotton rolls. All patients were given oral
hygiene instructions with special emphasis on cleaning proximal surfaces with an interdental brush and dental
floss. Patients were recalled at 6-month intervals for oral hygiene and RBFPD evaluations. RBFPD was not
examined for pontic fracture but just for debonding of the framework, since the number of veneered pontics wasless than half of all the RBFPDs. Framework debonding was determined by probing the interface between theretainer casting and the tooth with an explorer tip. Restorations that exhibited debonding but no major defects
were rebonded.
Survival was therefore evaluated at two levels: (1) complete and (2) functional survival. A restoration wasrecorded as having completely survived if no loss of retention was detected. Functional survival reflectedsurvival of functioning restorations, but after loss of retention on one occasion and successful rebonding of theoriginal restoration with the same bonding system. The baseline for assessment of both complete and functional
survival was the date of insertion of the original prostheses. In cases where a RBFPD was dislodged or where
one/both sides of a framework were loose or debonded from one or all abutment teeth, it was considered a failure(end-point). However, if a restoration was able to be rebonded successfully, the loosing/debonding was notconsidered a failure of functional survival.

Other problems such as fracture of the pontic or aesthetic

deterioration were not considered failures.

Missing data were censored at the date of the last available

information. Kaplan-Meier survival analysis

30

was performed with statistical software (Statview Ver. 5, SAS

Institute Inc., Cary, NC and SPSS 10.0 for Windows, MapInfo Corp., Troy, NY, USA). The clinical protocol
was approved by the Ethical Committee for Clinical Practice of the Nagasaki University Hospital of Medicine
and Dentistry (Approval No. 23).

Results
Twenty of the 99 (20.2%) patients were declared dropouts. A review of the clinical records of these patients,
who did not attend for examination, determined that they had never appeared for their recall appointment after
the insertion. For a better completeness of our analysis, we sought to interview these 20 patients by telephone or
mail; three patients had died and 1 had gone overseas after the treatment. One patient responded that the RBFPD
for a maxillary left premolar had been clinically retentive for 15 months, and another that the RBFPD had been
removed for an implant treatment at another hospital approximately two years after the initial insertion. The

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Int Chin J Dent 2006; 6: 53-59.

remaining 14 patients could not be reached by telephone or mail; the probability being that they had moved to
unknown addresses. Although the dropouts before our evaluation might result in some attrition bias, information
regarding these 20 patients was excluded from our analysis as the aim of the study was in essence an explanatory

100

100

80

80
Survival (%)

Survival (%)

trial.

60
40

40
20

20
0

60

0

0

20

40

60

80

100

120

140

160

180

0

20

40

Time (month)

MaxillaSurvival (%)

Survival (%)

100

60
40

A
0

140

160

180

200

posterior
Anterior

80
60
40

0
20 40 60 80 100 120 140 160 180
Time (month)100

2 missing teeth
1 missing tooth

80

B
0

Survival (%)

Survival (%)

100

60
40

20 40 60 80 100 120 140 160 180
Time (month)
3 abutment teeth

80

2 abutment teeth

60
40
20

20
0

120

20

20
0

100

Fig. 2. Overall functional survival.

Mandible80

80

Time (month)Fig. 1. Overall complete survival.

100

60

C
0

0
20 40 60 80 100 120 140 160 180
Time (month)D0

20 40 60 80 100 120 140 160 180
Time (month)Fig. 3.
A: Functional survival in relation to the missing tooth/teeth (maxilla or mandible). Debonding number and percent censored formaxillary RBFPDs were four and 91.8%,; while those for mandibular RBFPDs were none and 100%, respectively.
B: Functional survival in relation to the location (anterior or posterior) of the missing tooth/teeth. Debonding number and percent
censored for anterior RBFPDs were two and 93.8%,; while those for posterior RBFPDs were two and 95.8%, respectively.
C: Functional survival in relation to the number (one or two) of missing teeth. Debonding number and percent censored for
RBFPDs for one missing tooth were four and 93.7%,; while those for RBFPDs of two missing teeth were none and 100%,
respectively.
D: Functional survival in relation to the number (two or three) of abutment teeth. Debonding number and percent censored for
RBFPDs of two abutment teeth were four and 93.7%,; while those for RBFPDs of three abutment teeth were none and 100%,
respectively.

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Int Chin J Dent 2006; 6: 53-59.

Among the 81 prostheses assessed, no frameworks had fractured, but debonding occurred in a total of five
restorations (debonding rate: 6.2%). Of the five debonded restorations, one occurred as a result of trauma at 157
months. The RBFPD, which replaced a missing maxillary lateral incisor, was able to be rebonded since theabutment teeth exhibited no defects or aesthetic problems and periodontal supports were sufficient. Of the fivedebonded restorations, the remaining four could not be rebonded since secondary caries occurred in each
restoration as a result of bonding failure at the tooth-resin interface.

For the four RBFPDs, three newconventional FPDs and one new RBFPD were refabricated.
Figs. 1 and 2 show the complete and functional survival curves, respectively. The observation duration andcorresponding survival ratio for complete survival were 165 months and 43.9%, and those for functional survival
were 178 months and 87.7%. Fig. 3 shows Kaplan-Meier functional survival curves of the RBFPDs in relation
to the missing tooth/teeth, the location and the number of missing teeth and abutment teeth. Although thesurvival curves showed different tendencies, these factors had no statistical affect on longevity. Additional
analyses could not be carried out due to the infrequency of dedonding.

Discussion
RBFPDs made from a silver-palladium-copper-gold alloy were clinically followed-up for a maximum of 178
months (14.8 years). Although positive effects of tooth preparation have been found in previous studies,1,9,11,12
minimal preparation without a groove26 was carried out in the present study to conserve tooth structure. The
debonding rate of 6.2% obtained here was lower than those observed in other studies,15,31 and retention of therestorations was thought to be favorable.
Hansson evaluated the longevity of resin-bonded prostheses made of a high-gold alloy, the inner surface of
which was treated with air abrasion using aluminum oxide and high-temperature oxidation.31 The averagesurvival period of the RBFPDs was only nine months, and therefore it was suggested that adhesion ofresin-bonded prostheses must be based on mechanical retention between the TBB-initiated Super-Bond C&B
material and gold alloy selected because of the low durability of bonding joints to water. Tanaka et al. afterward
confirmed that the low bonding durability of Super-Bond resin joined to heated gold alloy was the result of
insufficient stability to acid attack of the oxidized copper oxide layer that forms on the gold alloy surface during
heating.32
Application of metal alloy conditioners for chemical bonding would help improve the overall results. Twothione primers are reported to enhance bonding durability between dental alloys and Super-Bond C&B adhesivematerial,21 and also showed excellent bond strength for silver-palladium-copper-gold alloys.33,34 This highbonding durability is accurately reflected in the results of this study, as all bonding failures were the result ofdebonding at the tooth-resin interface. However, the bond strength of resin and dental metal alloy decreases
after repetitive thermocycling, regardless of the application of the two thione primers.32 This has been reported
previously for V-Primer.35 Although the results of this study did not indicate the need to improve the primer,
treatment of the inner surface of the retainer should be carefully selected to facilitate longevity.

The

development of a noble metal primer in the future should lead to a more satisfactory prognosis for RBFPDs. The
importance of the type of dental alloy selected is also reflected in the current results. Restorations made fromsilver-palladium-copper-gold alloy might be naturally superior to those made of base metal alloys such as
nickel-chromium or cobalt-chromium. Hikage et al. reported that the survival rate of silver-palladium-copper-

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Int Chin J Dent 2006; 6: 53-59.

gold alloy was not statistically different from that of metal-ceramic gold alloys.24
The effect of restoration location is reportedly significant; in general, maxillary posterior restorations haveshown better retentive results than mandibular resotrations.13-15,17,18 However, in this study, the effect of location
was not significant, since the debonding rate was too low to statistically evaluate the influence on functional
survival time. Similarly, no other factor was shown to statistically affect the results. Nevertheless, debonding/loosing actually occurred, and debonded/loosened RBFPDs could not always be rebonded. Partial debonding
could easily be missed at a recall or subsequent examination by a dentist, probably since the debonding area
could be imperceptible and the debonded/loosened RBFPD probably not detached. Generally, there is in theory
a greater possibility of rebonding an RBFPD compared with a conventional FPD.

Although the clinicalexaminations in this study could not specify the causes of the bonding failures, the results of the study still
indicated the difficulty of reusing a RBFPD.
Within the limitations of this study, the minimal preparation, without any additional mechanical retention
between the dental alloy and the luting agent and without additional preparation of the abutment teeth including
groove or extensive preparation, was thought to be acceptable in light of the high survival rate. Additional toothpreparation is an obviously contradiction to the concept of minimal intervention. Yet, the results here showed
another problem where partial debonding of the RBFPD framework might cause secondary caries that prevent
rebonding (functional survival).

Clinicians should pay special attention and try not to miss any barely

perceptible debonding of an RBFPD when undertaking oral hygiene treatment; as well, they should be awarethat the prognosis for a RBFPD depends substantially on the selection of the framework alloys, the type ofprimer and luting agent, and proper surface preparations of adherent surfaces. The results here also indicate thatfurther improvements to the RBFPD bonding system are needed.
Acknowledgment
This study was supported in part by a Grant-in-Aid for Scientific Research C 17592030 (2005-2007) from the Japan
Society for the Promotion of Science (JSPS).

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Correspondence to:
Dr. Naomi TanoueDepartment of Specialized Dentistry, Nagasaki University Hospital of Medicine and Dentistry
1-7-1, Sakamoto, Nagasaki 852-8588, Japan
Fax: +81-95-849-7689 E-mail: t-naomi@net.nagasaki-u.ac.jp
Received March 15, 2006. Accepted April 17, 2006.
Copyright ©2006 by the International Chinese Journal of Dentistry.

59