Isfahan University of Medical SciencesDental Research Journal1735-33278120110319Effect of Postoperative Bleaching on Microleakage of Etch-and-Rinse and Self-etch Adhesives303303ENVajihesadatMortazaviProfessor, Department of Operative Dentistry and Torabinejad Dental Research Center, School of Dentistry, Isfahan University of Medical Sciences, Biomaterials Research Group, Department of Materials Engineering, Isfahan University of Technology, Isfahan, Iran. Professor, Biomaterials Group, Department of Materials Engineering, Isfahan University of Technology, Isfahan, Iran.. v_mortazavi@dnt.mui.ac.irMohammadhosseinFathiFereidonSoltani2011031920110319Background: Bleaching the discoloured teeth may affect the tooth/composite interface. The aim of this in vitro experimental study was to evaluate the effect of vital tooth bleaching on microleakage of existent class V composite resin restorations bonded with three dental bonding agents.     Methods: Class V cavities were prepared on buccal surfaces of 72 intact, extracted human anterior teeth with gingival margins in dentin and occlusal margins in enamel, and randomly divided into 3 groups. Cavities in the three groups were treated with Scotch bond Multi-Purpose, a total etch system and Prompt L-Pop and iBond, two self-etch adhesives. All teeth were restored with Z250 resin composite material and thermo-cycled. Each group was equally divided into the control and the bleached subgroups (n = 12). The bleached subgroups were bleached with 15% carbamide peroxide gel for 8 hours a day for 15 days. Microleakage scores were evaluated on the incisal and cervical walls. Data were analyzed using Kruskal-Wallis, Mann-Whitney and Bonferroni post-hoc tests (α = 0.05). Results: Bleaching with carbamide peroxide gel significantly increased the microleakage of composite restorations in Prompt L-Pop group at dentinal walls (P = 0.001). Bleaching had no effect on microleakage of restorations in the Scotch bond Multi-Purpose and iBond groups. Conclusion: Vital tooth bleaching with carbamide peroxide gel has an adverse effect on marginal seal of dentinal walls of existent composite resin restorations bonded with prompt L-Pop self-etch adhesive. Keywords: Bonding agents, Composite resins, Dental Adhesives, Dental Etching, Dentin, Tooth Bleaching.