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©Operative Dentistry, 2008, 33-1, 37-43 SUMMARYThis in vitro study evaluated the effect of technique, use of a bevel and thermal cycling on the fracture resistance and gap formation of resin composite MOD restorations. Fracture resistance was measured on standard MOD cavities prepared in 100 upper premolars that were stored for 24 hours and 6 months with 1000 thermal cycles. Subgroups (n=10) were: beveled or nonbeveled preparations and direct restorations (Adper Single Bond/Filtek Z250) and indirect restorations (prepolymerized Filtek Z250 cemented with Rely X ARC). Ten sound teeth and 10 specimens with MOD preparations without restorations served as the positive and negative controls, respectively. The specimens were subjected to axial compression in a universal testing machine at a crosshead speed of 0.5 mm/minute. Failure patterns were analyzed by stereomicroscopy (40x). To evaluate gap presence or absence, proximal box cavities were prepared in 24 human third molars that were restored as described above. The specimens were evaluated under SEM examination after 24 hours and six months. Data were statistically analyzed by ANOVA and multiple comparison tests at the 0.05 level of significance. After 24 hours, the beveled restorations exhibited higher fracture strength values than the non-beveled restorations, and all groups FH Coelho-de-Souza • GB Camacho FF Demarco • JM Powers Clinical RelevanceBeveling of the cavosurface margin can improve resistance to fracture and the marginal adaptation of posterior composite restorations, reducing the deleterious effect of storage with thermal cycling on restoration quality. Generally, indirect restorations showed similar performance compared to direct restorations.

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