Abstract: Objective: To analyze the effects of 10% carbamide peroxide at-home bleaching agents on the surface roughness and microhardness of direct and indirect composite resins. Methods: Four composite resin materials, i.e. two direct composite resins (Filtek Z350, Clearfil Majesty Ethetic) and two indirect composite resins (Ceramage, Adoro SR), were tested in our study. Twenty disk-shaped specimens (10mm in diameter and 1.0mm in thickness) for each resin material were prepared and randomly divided into two groups: 10% carbamide peroxide group and deionized water group (control group). The 10% carbamide peroxide agent was applied 8 hours daily during 14 days. The control specimens were immersed in deionized water throughout the experiment. Surface roughness and microhardness were measured before and after bleaching treatment. The data were analyzed using t test. Results: For exposure to 10% carbamide peroxide agent, only the Clearfil Majesty Esthetic composites resin presented a rougher surface after bleaching treatment (P<0.001). Microhardness of composite resins was not different throughout the 14-day period, regardless of the surface treatment. Conclusion: The application of 10% carbamide peroxide did not alter the microhardness of all tested composite resins. The surface microhardness was material-dependent.

Key words: Bleaching, Composite resin, Surface roughness, Microhardness