Aim: The aim of this study was to evaluate the effects of 2 bleaching agents on the surface roughness of nanofill composite resin finished with different polishing procedures. The hypothesis was that bleaching would have no effect on the surface roughness of the nanofill composite resin.

Materials and Methods: A total of 108-disc samples were prepared from a nanofill composite resin and randomly divided into three groups (n=36). Group I served as control group without polishing regimen. Group II was polished with Sof-Lex systems medium, fine and superfine alumi- num oxide-impregnated discs for 15s. Group III was polished with OneGloss discs for 30s. Following polishing, the baseline surface rough- ness values were measured using a profilometer. Then each group were further divided into 2 subgroups and bleached by one of the in-office bleaching agents tested. The Opalescence Boost and Opalescence Quick agents were applied on to the surface of the samples according to the manufacturer’s recommendations. At the end of the bleaching procedures, roughness was measured again. The statistical analysis was performed by Mann-Whitney U, Kruskal Wallis and Wilcoxon Signed Ranks test (p<0.05).

Results: After bleaching, surface roughness significantly increased in all groups compared to baseline (p=0.001). The highest mean initial surface roughness value was observed in OneGloss, followed by Sof-Lex and Control group (p<0.01). Among all groups, the % change in Ra values caused by the use of both bleaching agents was highest in the unpolished group (control) (p<0,01). In addition, no statistical difference was observed between the % change in Ra on the surfaces polished with Sof-Lex and OneGloss (p>0.05).

Conclusion: The hypothesis was rejected. The simulated bleaching with 40% HP or 45% CP increased the surface roughness of the nanofill composite. However, it has been observed that the Ra threshold value does not exceeded the clinically acceptable value of 0.2 μm after bleaching if an ideal finishing procedure was undertaken.