The impact of postoperative intracoronal bleaching on the microtensile bond strength at the composite-dentin interface

The study evaluated the effects of postoperative bleaching with HP and CP on microtensile bond strength (μTBS) and nanoleakage of composite restorations using total-/self-etch protocols. Sixty incisors with Black V cavities were restored using a multimode adhesive in total-/self-etch mode and resin composite. Samples were divided into five groups: control, CP×2, CP×5, HP×2, HP×5. After bleaching, 1×1×8 mm composite blocks (n=10) were tested for μTBS, and failure types were assessed. Two samples per group were analyzed for nanoleakage via scanning electron microscope (SEM). Two-way analysis of variance, Bonferroni correction, and stepwise linear regression were applied. CP×5 and HP×5 groups exhibited significantly reduced μTBS compared to control, and the self-etch protocol resulted in lower values regardless of bleaching method. Regression analysis confirmed significant effects of adhesive (total-etch) and bleaching (CP×5, HP×5). A significant relationship was found between failure modes and bleaching methods for each adhesive protocol, with adhesive failures being the most frequent. SEM revealed nanoleakage in all groups.