Margin analysis of posterior composites in vivo.

One of the major shortcomings of posterior composites is their tendency to shrink during polymerization. Thirty-three class II cavities were filled with Occlusin (OCC) (12), Coltène EX-D2 (CEX) (10), and Dispersalloy (AM) (11). The composites were placed in beveled, enamel-etched cavities by means of an incremental technique. One week and seven mo after placement, replicas were obtained and quantitatively analyzed in the SEM. The composites showed higher percentages of "excellent margin" (EM) (OCC, 70.6%; CEX-D2, 66.6%) than AM (49.2%) at baseline (p less than 0.01) and after seven mo (p less than 0.01). During the experimental period, the percentage of EM decreased by 10% for AM and OCC and by 14% for CEX-D2 (p less than 0.01). With the composites, an increase of "submargination" (SM) was found: OCC, 8.8%, and CEX-D2, 12.7%. An increase (11.2%) in margin fractures occurred for amalgam. Only OCC showed a low but significant increase (6%) in "marginal openings" (MO). This study confirms the inferior micromorphology of AM at the margins. The high amount of MO with the resin composites (16% after seven mo) indicates that, despite the complicated application technique, leakage of the restorations will occur. The margin analysis showed SM (OCC, 18%; CEX-D2, 21%) after seven mo, indicating severe wear. Class II amalgam restorations should not be replaced with the composites used in this study.