Margin quality of Class III and IV composites in vitro

Polymerization shrinkage and thermal expansion/contraction of composites counteract marginal bonding. The purpose of this study was to determine the margin quality of Class III and IV microfilled and hybrid composite restorations placed with adhesive techniques. Two experiments were conducted. In experiment 1, small, beveled Class III cavities were prepared in 24 incisors. Twelve cavities were filled with an experimental microfilled composite (COMPAFILL) and 12 with a control microfilled material (DURAFILL). In experiment 2, standardized large, beveled Class IV cavities were prepared in 24 incisors. Twelve of these incisors were filled with DURAFILL and 12 with the hybrid composite HERCULITE XR. The teeth were stored in water for 21 days. Before and after the restorations were thermocycled (5 degrees C-55 degrees C), replicas were obtained for quantitative analysis in the SEM. Statistical analysis (non-parametric tests, p less than 0.05) revealed that the two microfilled materials behaved very well (greater than 95% excellent margins) in Class III restorations before being thermocycled. After the restorations were thermocycled, the margin quality of DURAFILL decreased to 90% excellence, due to the increase in restoration fractures. Thermocycling did not affect the margin quality in the Class IV cavities, and the hybrid composite showed superior margin qualities (89% excellent). Better margin qualities were obtained in Class III cavities. Class IV restorations showed more overhangs (12%) and submargination (6%) which were technique-related. In no cases were greater than 1% marginal openings found.