In vitro microleakage of composite restorations after nonvital bleaching

Objective: After bleaching treatment, esthetic restorations often need to b e replaced due to color changes. Some papers have shown alterations in the bond of adhesive restorations to bleached teeth. The purpose of this study was to evaluate tooth and resin composite adhesion when submitted to nonvit al dental bleaching. Method and materials: One hundred and twenty bovine te eth were assigned to 3 groups (n = 40). paste of sodium perborate and water ; 37% carbamide peroxide gel; and no bleaching (control). After 3 weeks of continuous bleaching treatment, standardized Class V cavities were prepared at the cementoenamel junction and restored with Single Bond adhesive syste m and Z100 resin composite. The samples were thermocycled 1,500 times (5 +/ -: 1 / 55 +/- 1 degreesC) with a 1-minute dwell time. Then, they were immer sed in a 2% methylene blue solution (pH 7) for 4 hours, sectioned, and anal yzed by stereomicroscopy. Microleakage analyses were done, using scores fro m 0 to 4, considering leakage on the incisal wall (enamel) and the cervical wall (dentin). Data were analyzed by Kruskal-Wallis and Mann-Whitney tests (alpha = 0.05). Results: The results showed that sodium perborate and carb amide peroxide gel significantly increase the microleakage in Class V resin composite restorations to dentin but not to enamel margins. Conclusion: Th e risk of microleakage in dentin margins is increased soon after bleaching treatment.