BACKGROUND AND OBJECTIVE: wear is the one of factors which can influence on the clinical performance of composites. Tooth bleaching agents can effect on these materials. The aim of this study was the comparison of the effect of different bleaching regimes of carbamide peroxide on wear of Z250 composite.

METHODS: in this in vitro study, 40 disk shape sample of Z250 were made with 7mm in diameter and 2mm in thickness by plastic molds. Samples divided in 4 groups randomly (n=10): In first group (control group), samples were toothbrusted (for 20000 cycles) with no carbamide peroxide (were kept in 37 °C distilled water for two weeks), in second group, samples that were tooth brusted with 10% carbamide peroxide (4 hours daily for 2 weeks). In third group samples were toothbrusted with 16% carbamide peroxide (3 hours daily for 2 weeks). Fourth group were toothbrusted with 22% carbamide peroxide (1 hour daily for 2 weeks) Weight of samples were recorded before and after wear test.
FINDINGS: The mean of weight loss (gr) of samples in control group was 0.001±0.0016, for second group was 0.0048±0.0089, for third group was 0.0013±0.0025 and for fourth group was 0.0005±0.0002. There were decrease in samples wear with increasing of peroxide concentration but this difference was not statistically significant.
CONCLUSION: Based on the findings of this study, carbamide peroxide 10%,16% and % had no effect on tooth brush wear rate of Z250 composite.