Efficacy of Beveling Posterior Composite Resin Preparations Barry P. lsenberg, D.M.D., M.A.
Karl F. Leinfelder, D.D.S., M.S.
A clinical study was conducted to evaluate the controversy over the need to bevel the occlusal cavosurface margins of posterior composite resin preparations. A total of 43 standard amalgam type cavity preparations were generated. On a randomized basis the preparations were either beveled or left unmodified. The width of the bevel in each case approximated 1 pm. Impressions were made of each preparation to verify occlusal dimension. Each preparation was restored with Estilux Posterior (Kulzer, Inc.) using conventional techniques. Polyvinyl siloxane impressions were generated and then cast with die stone. These casts were evaluated for wear at baseline, 6 months, 1, and 2 years. The loss of composite resin in the beveled preparation at 2 years averaged 8 1.2 pm while the nonbeveled averaged 69.8 pm. On the basis of this study, it was concluded that beveling of the occlusal cavosurface did not enhance the wear resistance of the composite resin restoration nor any of the other clinical characteristics evaluated in the study.
reduce marginal tooth fracture. They also suggest that this final step in cavity preparation helps to eliminate degradation problems that may occur during the finishing process. Although most in vitro studies appear to have substantiated these concepts, little or no information is currently available regarding clinical behavior. It was the purpose of this study, then, to evaluate the effect of beveling on the long-term clinical performance of a posterior composite resin.
he use of posterior composite resins has grown at a considerable rate over a relatively short period of time. Although used by most of the dental profession over the last several years, little information is currently available regarding the most favorable type of cavity preparation. The one area, however, that has received considerable attention is the possible need for beveling of the occlusal cavosurface margin. Most studies dealing with posterior composite caviy preparations conclude that beveling enhances the longevity of the restoration. Isben and Neville,' as well as Welk and Laswell,2 have demonstrated that beveled margins exhibit less microleakage than those possessing a standard butt joint. It was hypothesized that beveling increases the surface area of the cut enamel thereby making it more difficult for fluids to penetrate the dentin junction. Craig3 and Lorton and Brady4 have shown that the end of the enamel rods are more amenable to the etching process as compared to the sides of the prisms. Since beveling of the occlusal cavosurface margin theoretically tends to expose the ends of the enamel rods at least obliquely, beveling has long been recommended by clinicians and manufacturers as well. Finally, Lun5 as well as Oil0 and Jorgensen6 state that beveling of the cavosurface margin is necessary to
MATERIALS AND METHODS A total of 43 Class I and Class I1 cavity preparations was generated in a series of adult patients. The preparations conformed to those normally used in con junction with amalgam restorations. The ratio of Class I to Class I1 was approximately 50:50. O n a randomized basis one-half of the restorations were beveled along the occlusal cavosurface angle. The other half were prepared without beveling. Instead, the cavosurface angle formed a butt-joint with the restorative material. In each case the bevel was established to a width of approximately 1.0 mm using a fine particle tapered diamond bur (1 DT). Immediately after preparation, a polyvinyl siloxane impression (Reprosil, L. D. Caulk, Milford, DE) was made of each prepared cavity. This procedure was carried out for two reasons. The first was to document the width of the bevel whereas the second was to determine the size of the preparation itself. At this point, all of the preparations were classified or categorized according to the average dimension of the isthmus on the occlusal surface.
Unisasity of Alabama School of Dentisny, Birmingham, Alabama A i d i e rePrinr ~~ reguens to Dr. Barry P. Isenberg, Department of Rercor-, Unipenirlr of Alabama School of Dendsuy, Birmingham, AL 35294 O 1990 B. C Daker k.
Efficacy of Beveling Posterior Cornposire Resin Preparations
Table 1. Classification of Cavity Size
Next, the enamel walls of the preparation were acid etched with a 37 percent solution of phosphoric acid. After washing and drying, an enamel bonding agent was applied followed by conventional matrixing and wedging. All of the preparations, beveled and unbeveled, were restored with Estilux Posterior CVS (Kulter, Inc., Irvine, CA). Only one type of posterior composite resin was included in the study. In each case the composite resin was inserted segmentally. Each increment was photocured for at least 20 seconds whereas the final surface was cured for 1 minute. Finishing and polishing was carried out using the 12-bladed finishing carbide burs and Sof-flex finishing discs (3M Co., St. Paul, MN) respectively. Upon completion, each restoration was impressed with a polyvinyl siloxane impression material (Reprosil, L. D. Caulk) and then cast with a die stone (Velmix, Kerr Manufacturing Co., Romulus, MI). These die stone casts were then used for determining loss of material from the occlusal surface. This was accomplished by comparing each cast against a series of calibrated optical standards. The M-L Scale (MoffaLugassy)’ was selected on the basis that a number of other posterior composites had been evaluated with this system in our facility. Also, clinical photographs were generated for all restorations as well as direct evaluations at each recall period. In addition to the indirect methods of evaluation, all restorations were evaluated in accordance with the USPHS criteria as described by Cvar and Ryge.8 The characteristics evaluated included the following:
Cavdy Prepraiion Wdth
1 2 3
1-2 mm 2-4 mm 4+mm
Bevel x Group 2.1 (0.6)
x Group 2.1 (0.91
Particular attention was given to the areas along the occlusal cavosurface margin.
RESULTS The general classification of cavity size and distribution of samples is presented in Table 1. Those preparations averaging 1 to 2 mm fell into group one. Those in which the isthmus was 2 to 4 mm fell into group two. Those in which the isthmus was greater than 4 mm were included in group three. As can be seen, the average dimension of both the bevel and nonbeveled preparations across the occlusal isthmus were almost identical. The mean category value for the intercavosurface margin was 2.1 mm.
Direct CIinicaI EvaIuation The clinical evaluations for color-matching ability, interfacial staining, and secondary caries were the same for all restorations regardless of the type of cavity preparation. Specifically, throughout the 2 years of evaluation, all three characteristics were rated as clinically ideal or “alfa.” The direct evaluation results for wear or loss of anatomic form, marginal adaptation, and surface texture are presented in Table 2. Although the percent of alfa ratings for the no bevel condition was slightly less than that for the beveled conditions, the difference was not statistically significant. Also, as can be seen in Table 2, the percent “alfa” ratings for both marginal adaptation and surface texture were nearly identical for the restorations associated with either type of cavity preparation.
1. 2. 3. 4.
color matching ability, interfacial staining, secondary caries, loss of anatomic form, 5. marginal adaptation, and 6. surface texture.
Evaluations were conducted at the time of insertion and again at 1 and 2 years. Additionally, a number of extracted teeth were prepared for Class I and Class I1 cavities, etched with a 37 percent solution of phosphoric acid, washed, and then dried. The teeth were then sectioned mesiodistally and evaluated with SEM for the purpose of determining enamel rod orientation with respect to various surfaces of the cavity preparation.
Indirect Clinical Evaluation The results of the indirect evaluation for wear as determined by comparing the casts to the M-L scale are presented in Figure 1. At the end of the first year the loss of material at the cavosurface margin was 30.6 (a = 18.9) micrometers for the standard preparations and
Table 2. Percentage of Restorations Exhibiting Alfa Values Categories
Baseline 1Year 2 Years
100 83 56
100 92 100
100 92 100
100 15 25
100 17 25
JOURNAL OF ESTHETIC DENTISTRYNOLUME 2, NUMBER 3 lMuyl]une I990
T i (rnbc;)
Figure 1. Effect of beveling the occlusal cavosurface angle on wear.
Wear (micrometers) Beveled
42.1 (u = 22.5) micrometers for the beveled cavity preparations. At the end of 2 years the values increased to 69.8 (cr = 26.8) and 81.2 (cr = 26.1) respectively. A distribution of the samples with respect to wear at the end of 2 years is presented in Figures 2 and 3. Sample distribution for the nonbeveled preparations is illustrated in Figure 2 whereas the beveled preparations are represented in Figure 3. While the distribution curve for the nonbeveled preparations is quite normal, that for the beveled restorations appears for some reason to be skewed to the right. Based on the distribution of values about the mean for both types of cavity preparations, the differences for the two conditions were not statistically significant. Interestingly, the mean value for wear observed in this study was approximately the same as that already re40
Figure 3. Distribution of restorations (beveled) with respect to wear at 2 years.
Figure 4. SEM of enamel rod orientation at the cavosurface angle area.
ported for Estilux Posterior in other studies when evaluated over the same period of time.9910
SCANNING ELECTRON MICROSCOPY
A typical orientation of the enamel rods in the area of the cavosurface margin along the buccal and lingual walls of the cavity preparation is illustrated in Figure 4. Note that contrary to the diagrammatic illustrations represented in most text books of operative dentistry, the enamel rods do not present a preferred orientation of parallelism directed to the occlusal surface. This type of pattern, which was fairly consistent, repeated itself along the entire length of the cavosurface margins.
Figme 2. Dismbution of restorations (nonbeveled) with respect m weat at 2 yean.
From the results of this study it is apparent that beveling of the occlusal cavosurface margin had no 72
Efficacy of Beveling Posterior Composite Resin Preparations
clinically significant effect on the performance of the posterior composite resin. Specifically, ,at the end of 2 years, no differences could be detected in color matching ability, microleakage, caries, wear, or marginal adaptation. The two different styles of cavity preparations investigated in this study resulted in restorations, in which clinical characteristics were indistinguishable from one another. In view of the results obtained it is recommended that the occlusal margin should not be beveled. A number of reasons may be given. First, any beveling, regardless of its width, automatically increases the dimension of the cavity preparation. Doing so, of course, increases the probability of incorporating the centric stops on the surface of the restoration. Such a condition causes the rate of wear to increase substantially. Another problem associated with beveling the cavosurface margin relates to the technique of standardizing its width. Frequently the clinician extends the bevel to dimensions well beyond 1 mm. Still another problem associated with beveling is the degree of difficulty in establishing the exact margin or interface of the final restoration. Commonly they are more difficult to establish than those with a 90 degree angle. Furthermore, based on the orientation of the enamel rods along the cavosurface margin, beveling certainly would not increase the probability of bonding to the ends of the enamel rods. Finally, since beveling involves a greater surface area of the occlusal surface, it is probable that the process may enhance straining or deformation of the buccal and lingual cusps during polymerization of the resin. Such a condition has been shown to stimulate postoperative sensitivity.
clinically significant effect on the performance of posterior composite resins. Specifically, no clinically significant difference could be detected in color matching, microleakage, caries, wear, or marginal adaptation. On the basis of these results, then, it is suggested that beveling of the occlusal cavosurface angle should not be carried out.
References 1. Isben RL, Neville K. Adhesive restorative dentistry. Philadelphia: WB Saunders, 1974. 2. Welk DA, Laswell HR. Rationale for designing cavity preparations in light of current knowledge and technology. Dent Clin North Am 1976;20:231. 3. Craig RG. Restorative dental materials. 6th ed. St. Louis: C.V. Mosby, 1980. 4. Lorton L, Brady J. Criteria for successful composite resin restorations. Gen Dent 1981;29(3):234. 5. Lutz F. Beitrage zur Entwicklung von Seitenzahn-Komposits. Zahnarztl Inst KAR PAR PZM Zurich (ISBN 3-85656-004-1) 1980. 6. Oil0 G, Jorgensen KD. Effect of bevelling on the occurrence of fractures in enamel surrounding composite resin fillings. J Oral Rehabil 1977;4:305-309. 7. Lugassy AA, Moffa JP. Laboratory model for quantification of clinical occlusal wear. J Dent Res 1985;64:181, Abst. N o 63. 8. Cvar JR, Ryge G. Criteria for the clinical evaluation of dental restorative materials. US Department of Health, Education and Welfare, Publication No. 790:244, 197 1. 9. Wilder AD, May KN, Leinfelder KF. Three year clinical evaluation of U-V cured posterior composite resins. J Prosthet Dent 1983;50:26-30. 10. Timmon JH, Skeertevs TM, Richards ND, Mitchell RJ, Leinfelder KF. Two studies of a composite resin in posterior teeth. J Dent Res 1986;65:126, Abst. No. 1203.
CONCLUSIONS Beveling the occlusal cavosurface margin had no