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An Analysis of Clinical Studies on Resin-bonded Bridges N.H.J. Creugers and M.A. Van 't Hof J DENT RES 1991 70: 146 DOI: 10.1177/00220345910700021001 The online version of this article can be found at: http://jdr.sagepub.com/content/70/2/146

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An Analysis of Clinical Studies on Resin-bonded Bridges N.H.J. CREUGERS and M.A. VAN 'T HOF' Department of Oral Function and Prosthetic Dentistry, Dental School, Philips van Leydenlaan 25, 6525 EX Nijmegen, The Netherlands; and 'Department of Medical Statistics, TRIKON: Institute for Dental Clinical Research, University of Nijmegen, The Netherlands

Many clinical data on resin-bonded bridges (RBBs) have been published in the last ten years. The survival rates vary widely, and the conclusions are sometimes conflicting. A method of combining the results of different studies in order to draw conclusions about the effectiveness of therapeutic concepts is meta-analysis. The aims of the meta-analysis in this study were: (1) to assess an "overall" survival ratio for RBBs and (2) to explore relationships between potential success factors and reported survival times. About 60 publications with clinical data on RBBs were reviewed. Following a number of inclusion criteria (information adequate to calculate or assess survival rates, as well as adequate information about the patients, the designs, and types of RBBs), 16 different samples were used for this meta-analysis. A weighted multiple-regression analysis revealed no significant effects of "type of retention" and "location" on the survival percentages. Kaplan-Meier estimates were used to assess overall survival in a secondary analysis with the data from all 16 samples (n = 1598). The overall survivals were: one year, 89 ± 1%; two years, 84 ± 1%; three years, 80 + 1%; and four years, 74 ± 2%.

J Dent Res 70(2):146-149, February, 1991

Introduction. Clinical data on the efficacy of resin-bonded bridgework have been published by many workers. An up-to-date overview of the literature has been published in English (Saunders, 1989). Overviews of clinical results have also been presented by Marinello et al. (1987) and Edwards et al. (1989). A review of the literature of the past ten years revealed about 60 publications presenting clinical data. Some retrospective studies now reach about ten years' follow-up (Williams et al., 1989; Thompson et al., 1989), while some clinical trials have run for about six years (Creugers et al., 1989a). The survival rates vary widely, and the conclusions are sometimes conflicting. Besides considerable differences in technical and clinical procedures, differences in study characteristics may also be responsible for this variation. The large diversity in the presentation of the results complicates direct comparisons of the longitudinal data. A method of combining the results of different studies in order to draw conclusions about the effectiveness of a procedure is the so-called meta-analysis method (e.g., L'Abbe et al., 1987; Chalmers et al., 1987a, b). The importance and use of meta-analysis in putting together scientific data have recently been reviewed (Mann, 1990). This study presents an analysis of the clinical data on resinbonded bridges since 1980, using the systematic reviewing strategy required in meta-analysis. The aims of the analysis were: (1) to assess an "overall" survival ratio of three- or four-unit cast resin-bonded bridges and (2) to explore relationships between potential success factors and the reported sur-

vivals. The following potential success factors were considered: type of retention, cementation material, preparation of the abutment teeth, mobility of the abutment teeth, presence of restorations in the abutment teeth, and location of the bridge.

Materials and methods. Data collection.-In the literature of the past ten years, 60 publications were found that contained clinical data on cast resin-bonded bridges. These publications were interim as well as final reports of 25 different clinical studies. This means that some of the publications were dealing with the same set of patients. As proposed by L'Abbe et al. (1987), reports dealing with the same set of patients were grouped, and reference was made only to the most recent publication of that study. In this way, 25 studies with different samples of patients were identified and collected prior to the selection for meta-analysis. Following the objectives of this study, the inclusion and exclusion criteria for selection of data sets were: (1) The minimal follow-up period should be at least one year; (2) the publication should provide relevant information about the patients and the patient selection, for exclusion of extremely selected samples (i.e., children, high-risk groups, etc.); (3) the publication should present survival rates and confidence intervals or should contain appropriate information to calculate or assess survival rates and confidence intervals (life tables); (4) there should be relevant information about the designs and the retainer types of the bridges involved. The results of the study should be related to three- or four-unit bridges; and (5) the publication should give information about the location of the bridges in the jaws. Table 1 gives an overview of the collected and the selected studies as well as the reasons for exclusion. On the basis of the criteria listed above, 14 of the 25 studies were excluded from further analysis. The selected studies were reviewed, and summary information was abstracted. The only characteristics with potential influence on the durability that were given in all the selected studies were "type of retention" and "location of the bridge". Other potential success factors-such as "preparation of the abutment of teeth" and "cementation material"-were not .

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Received for publication June 15, 1990 Accepted for publication November 29, 1990 146

Fig. 1 -Overall survival of all resin-bonded bridges evaluated (n 1598) (vertical bars indicate 95% confidence intervals).

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described adequately in all studies and were therefore not used in the analysis. The result was that a total of 16 different (sub)groups of patients with resin-bonded bridges could be identified for the analysis. Table 2 presents the 11 selected studies with (sub)groups of patients according to the two key characteristics. Two studies included some bridges of more than four units or bridges with crown retention by one retainer. These bridges were excluded from further analysis. Statistical methods.-For each study, the survival of the bridges was assessed by the method of Kaplan and Meier (1958). Asymmetrical confidence intervals were adapted from Geigy Tables (Diem, 1960). Weighted multiple-regression analysis was used to investigate the influences of the parameters "type of retention" and "location of the bridge" on the survival percentages. Weights were chosen depending on the width of the calculated confidence intervals. For assessment of the overall survival, a new data-set, including all data from the selected studies, was created.

147

for quality as presented by L'Abbe et al. (1987) and Chalmers al. (1987a, b) were followed in this study. Since only few data for this analysis were derived from controlled clinical trials, interpretation of the results should be restricted to general tendencies. In the authors' opinion, this analysis shows once again the need for controlled clinical studies when new restorative techniques are evaluated. The variation between survival rates in different studies may be a result of variation in patient selection, tooth preparation, luting resin cements, and operator's experience. As such, the overall success rate may be similar to the survival likely to be achieved in general practice. The longest follow-up period was ten years, and in about 50% of the cases, the follow-up period was at least five years. However, the calculated confidence intervals were such that presentation of survival rates of five years or over was meaningless, since only 41 bridges were followed for more than

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In general, the survivals in the retrospective studies

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not significantly different from those in the prospective studies.

Results. The data on 1598 resin-bonded bridges were analyzed. The multiple-regression analysis revealed no significant effects of the parameters "type of retention" and "location" on the survival percentages (p values >0.10). Fig. 1 presents the overall survival rates for times up to four years of follow-up. Fig. 2 is presented to demonstrate the heterogeneity of the studies. It shows the survivals of the different subgroups at the two-year follow-ups. Since the data of only seven out of 16 samples were useful for assessment of the four-year survival rate, an additional test was performed by comparing the short studies with the longer studies for (a) the one-year survival and (b) the characteristics given in Table 2. The result of this test was negative (i.e., no selective drop-out).

Discussion. In general, meta-analysis is observational research and, as such, is susceptible to numerous confounding factors. Among others, the most important dangers of bias are caused by the selection of the research data and by publication bias (i.e., omission of unpublished results). To minimize the possibility that bias might influence the results, methodologies for metaanalysis have been developed. Although there is no single "correct" method for performing meta-analysis, the guidelines

TABLE 1

COLLECTED AND SELECTED STUDIES REFERRED TO THE MOST RECENT PUBLICATION OF THE PARTICULAR STUDY, AS WELL AS REASON FOR REJECTION FROM THE METAANALYSIS ACCORDING TO THE INCLUSION AND EXCLUSION CRITERIA (LISTED CHRONOLOGICALLY)

Collected Study Livaditis (1981) Shaw and Tay (1982) Bergendahl et al. (1983) Eshleman et al. (1984) Chew (1985) Hamada et al. (1985) Hudgins et al. (1985) Pfeiffer (1986) Von Loges and Lode (1987) Kellet (1987) Holste et al. (1987b) Priest and Donatelli

Patient/ Sample Bridge Size Information + 57

-a

Survival Ratio -' detectable _2 detectable _3 -_ _2 given detectable

108 131 58

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given

33 216 122 525

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44

100 39 10 57 27 56 38

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2 2

Selected no yes no yes no no no yes no yes no no

(1988) Mohl et al. (1988) Van der Veen (1988) Clyde and Boyd (1988) Yamashita and Yamani

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(1988) Thompson and Wood

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(1988) Al-Shammery and Saeed (1989) Berekally and Smales (1989) Creugers et al. (1989) Edwards et al. (1989) Ferrari et al. (1989) Paszyna et al. (1989) Williams et al. (1989)

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SUBGROUP Fig. 2-Survival percentage of resin-bonded bridges by subgroup and mean survival at two-year follow-up.

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Peters (1989) 52 + = include, - = exclude. (a) Uncommon retainer design and/or long-span bridges included/uncommon materials. (b) Inadequate information about location and/or bridge design. (c) Selective group of patients (i.e., high-risk group).

(1) Survival ratio not detectable; minimal follow-up, less than 12 months. (2) Survival ratio not detectable, age(s) at failure unknown. (3) Survival ratio not detectable, based on original and re-entered bridges.

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TABLE 2 OVERVIEW OF SELECTED STUDIES AND IDENTIFIED SUBGROUPS ACCORDING TO SOME KEY CHARACTERISTICS Location in Follow-up Retention Type§ Sample Group Type of % Anterior Max. Yrs. Size Number Study# Study (%) 100 p (100) 1 3.5 46 retro. Shaw and Tay (1982) 100 p (100) 39 3.5 2 retro. Eshleman et al. (1984) 100 s (90); e (10) 3 56 3 retro. Pfeiffer (1986) 95 e (100) 4.3 4 84 retro. Kellet (1987) 100 5 p (100) S 24 100 t (100) 3.3 84 6 prosp. Van der Veen (1988) 0 t (100) 3.3 7 68 100 p (100) 6 50 8 0 6 p (100) 14 9 45 4 e (100) 10 36 retro. Al-Shammery and Saeed (1989) 100 5 166 11 cl.tr. Creugers et al. (1989b) p (45); e (55) 0 5 37 12 p (45); e (55) e (25); s (25); o (50)* 50 5 514 13 prosp. Paszyna et al. (1989) 80 99 10 14 retro. Williams et al. (1989) p (72); e (28) e (100) 4 75 209 15 retro. Ferrari et al. (1989) 25 5 e (60); o (40) 52 16 retro. Peters (1990) Oe = etched; p = perforated; s = sand-blasted; t = tin-plated; o = others. #retro. = retrospective; prosp. = historical prospective; cl.tr. = clinical trial. *Based on information from Peters and Kerschbaum (1990). 11

The results in the small studies were almost similar to those in the large studies. However, Fig. 2 shows that interpretation of only one study may significantly mislead clinicians, especially with short-term results. From the potential success factors described in the literature, only the factors "type of retention" and "location of the bridge" were analyzed. Other possible success factors were not described adequately in all studies and therefore could not be analyzed. The weighted multiple-regression analysis did not reveal a detectable influence of the "type of retention" or "the location of the bridge" on the survival. Although clinical significance is not proven, this finding is of importance, since it allows an overall survival ratio to be assessed from the selected data. The overall survival curve (Fig. 1) shows an almost linear negative slope, resulting in a 74% survival rate at four years. REFERENCES L'ABBE, K.A.; DETSKY, A.S.; and O'ROURKE, K. (1987): Metaanalysis in Clinical Research, Ann Intem Med 107:224-233. AL-SHAMMERY, A.R. and SAEED, H.I. (1989): A Four-year Clinical Evaluation of Acid Etched Bridges, Saudi Dent J 2:56-59. BEREKALLY, T.L. and SMALES, R.J. (1989): A Retrospective Clinical Study on Resin Bonded Bridges, JDent Res 68:547, Abst. No. 70. BERGENDAHL, B.; HALLONSTEN, A.-L.; KOCH, G.; LUDVIGSON, N.; and OLGART, K. (1983): Composite Retained Onlay Bridges, Swed Dent J 7:217-225. CHALMERS, T.C.; BERRIER, J.; SACKS, H.S.; LEVIN, H.; REITMAN, D.; and NAGALINGAM, R. (1987a): Meta-analysis of Clinical Trials as a Scientific Discipline. II: Replicate Variability and Comparison of Studies that Agree and Disagree, Stat Med 6:733-744. CHALMERS, T.C.; LEVIN, H.; SACKS, H.S.; REITMAN, D.; BERRIER, J.; and NAGALINGAM, R. (1987b): Meta-analysis of Clinical Trials as a Scientific Discipline. I: Control of Bias and Comparison with Large Cooperative Trials, Stat Med 6:315-325. CHEW, C.L. (1985): The Acid-etched Fixed Partial Denture: a Twoyear Report, J Prosthet Dent 54:173-175. CLYDE, C.S. and BOYD, T. (1988): The Etched Cast Metal Resinbonded (Maryland) Bridge: A Clinical Review, J Dent 16:22-26. CREUGERS, N.H.J.; SNOEK, P.A.; VAN 'T HOF, M.A.; and KAYSER, A.F. (1989a): Clinical Performance of Resin-bonded Bridges: a 5 Year Prospective Study. Part I: Design of the Study and Influence of Experimental Variables, J Oral Rehabil 16:427436.

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An analysis of clinical studies on resin-bonded bridges.

Many clinical data on resin-bonded bridges (RBBs) have been published in the last ten years. The survival rates vary widely, and the conclusions are s...
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