Effect of waiting time for placing resin composite restorations after bleaching on enamel bond strength

This study investigated the influence of the waiting time for placing resin composite (RC) restorations after dental bleaching on the shear bond strength (SBS) to enamel. Seventy bovine incisors were obtained, of which 60 were stained in coffee solution for 1?week and then bleached with the whitening agent Lase Peroxide Sensy (DMC Equipments, Brazil), following the manufacturer directions of use. Next, all teeth were allocated into seven groups (n?=?10) according to the waiting time after bleaching for placing the RC: immediately (0?h), 24?h, 3, 7, 14 and 28?days (d). Ten teeth were not bleached to serve as control. The specimens were prepared for SBS test and also for failure mode analysis. Scanning electron microscopy images were taken in non-bleached and bleached specimens. Data was analyzed by one-way ANOVA and Tukey’s test (α?=?0.05). The SBS means (standard deviations), in MPa, were: control?=?8.5^b (5.8); 0?h?=?14.5^a (5.9); 24?h?=?18.8^a (7.4); 3 d?=?15.7^a (0.1); 7 d?=?15.6^a (7.0); 14 d?=?15.0^a (6.7); and 28 d?=?17.9^a (7.7). All bleached groups resulted in similar SBS to enamel (p?≥?0.221), but higher than the control (p?≤?0.004). Adhesive failures were predominant in all groups. Bleaching produced an acid-etching pattern (enamel prisms exposure) on enamel, differently to the non-bleached teeth, which showed an unaltered surface. In conclusion, dental bleaching did not affect resin-enamel bond strength, regardless of the waiting time to place the restoration after bleaching.