Marginal Integrity of Bulk Versus Incremental Fill Class II Composite Restorations

Bulk-fill composites have been introduced to facilitate the placement of deep direct resin composite restorations. This study aimed at analyzing the cervical marginal integrity of bulk-fill vs incremental and open-sandwich class II resin composite restorations after thermomechanical cycling using replica scanning electron microscopy (SEM) and ranking according to the World Dental Federation (FDI) criteria. Box-only class II cavities were prepared in 91 maxillary premolars with the gingival margin placed 1 mm above and below the cemento-enamel junction. Eighty-four premolars were divided into self-etch and total-etch groups, then subdivided into six restorative subgroups (n=7): 1-Tetric Ceram HB (TC) was used incrementally and in the open-sandwich technique with 2-Tetric EvoFlow (EF) and 3-Smart Dentin Replacement (SD). Bulk-fill restoratives were 4-SonicFill (SF), 5-Tetric N-Ceram Bulk Fill (TN), and 6-Tetric EvoCeram Bulk Fill (TE). In subgroups 1-5, Tetric N-Bond self-etch and Tetric N-Bond total-etch adhesives were used, whereas in subgroup 6, AdheSE self-etch and ExciTE F total etch were used. One more group (n=7) was restored with Filtek P90 Low Shrink Posterior Restorative (P9) only in combination with its self-etch P90 System Adhesive. Materials were manipulated and light cured (20 seconds, 1600 mW/cm(2)), and restorations were artificially aged by thermo-occlusal load cycling. Polyvinyl-siloxane impressions were taken and poured with epoxy resin. Resin replicas were examined by SEM (200×) for marginal sealing, and percentages of perfect margins were analyzed. Moreover, samples were examined using loupes (3.5×) and explorers and categorized according to the FDI criteria. Results were statistically analyzed (SEM by Kruskal-Wallis test and FDI by chi-square test) without significant differences in either the replica SEM groups (p=0.848) or the FDI criteria groups (p>0.05). The best SEM results at the enamel margin were in TC+EF/total-etch and SF/total-etch and at the cementum margins were in SF/total-etch and TE/self-etch, while the worst were in TC/self-etch at both margins. According to FDI criteria, the best was TE/total-etch at the enamel margin, and the poorest was P9/self-etch at the cementum margin. Groups did not differ significantly, and there was a strong correlation in results between replica SEM and FDI ranking.