Dentin µTBS and Hardness of Bulk-fill and Conventional Composites Placed in a Box-shaped Cavity Preparation.

PURPOSE: To compare the dentin microtensile bond strength (µTBS) and the Knoop hardness of bulk-fill and conventional restorative composites in box-shaped Class I cavities using different insertion techniques. MATERIALS AND METHODS: Forty box-shaped Class I preparatons 4 mm deep were performed in the pulp chamber of sound human third molars. The restorations were made using either a conventional microhybrid (Z250, 3M ESPE) or bulk-fill (Tetric EvoCeram Bulk-fill, TCBF) composite using two incremental thicknesses: 2 mm or 4 mm (n = 10). After 24-h water storage, the restorations were sectioned. The first slice (0.7 mm thick) taken from a proximal surface was submitted to the Knoop hardness (KHN) test at five depths from the occlusal cavosurface to the pulpal line angle. Sticks were fabricated from the remaining sections and tested for dentin microtensile bond strength (µTBS). Means were analyzed using two-way ANOVA and Tukey's test (p < 0.05). RESULTS: Higher (p < 0.05) µTBS resulted when both composites were restored with 2-mm increments, with no significant difference between materials (p > 0.05). Higher (p < 0.05) KHN means were found when 2-mm increments were used, with no significant differences (p > 0.05) between the materials. When the teeth were restored with one bulk increment (4 mm), the deeper layers presented lower KHN means (p < 0.05) starting at 2 mm for Z250 and 3 mm for TCBF. CONCLUSION: The 2-mm increment restorations in box-shaped cavities yielded higher µTBS and microhardness for conventional and bulk-fill composites.

Color stability of repaired composite submitted to accelerated artificial aging.

The aim of this study was to evaluate the color stability (ΔE) of nanoparticulate composite, with consideration for the type of surface treatment performed before repair. A Teflon matrix was used to fabricate 50 test specimens from composite. After initial color readout, the specimens were submitted to 100 hours of accelerated artificial aging (AAA). The samples were divided into five groups (n = 10), according to the surface treatment performed: sandblasting with aluminum oxide powder, phosphoric acid, and an adhesive system (Group 1); sandblasting with aluminum oxide powder, phosphoric acid, and a flowable composite (Group 2); abrasion with a diamond bur, phosphoric acid, and an adhesive system (Group 3); abrasion with a diamond bur, phosphoric acid, and a nanoparticulate composite (Group 4); and a control group (Group 5). After repair, a new color readout was taken, the test specimens were submitted to a new AAA cycle (300 hours), and the final color readout was taken. Comparison of the ΔE means (one-way ANOVA and Tukey tests, p < 0.05) demonstrated no statistically significant differences among the groups (p > 0.05) after 100 hours of AAA. After repair, Group 1 (4.61 ± 2.03) presented the highest color alteration with a statistically significant difference compared with the other groups (p < 0.05). After 300 hours, Group 4 specimens (13.84 ± 0.71) presented the lowest color alteration in comparison with the other groups, with a statistically significant difference (p < 0.05). It was concluded that the repair performed in Group 4 provided greater esthetic recovery, made possible by the regression in the ΔE values of the restorations after repair, and less color alteration of the restorations over the course of time.