---

ABSTRACT:
Background & Aim: One of the induced major problem after bleaching treatments is enamel surface roughness increase, which can lead to increased risk of dental caries, plaque accumulation and later enamel discoloration.In this study the effect of adding CPP-ACP to home bleaching gel on enamel roughness was evaluated.
Material & Methods: in this experimental study, premolar teeth have been used.The samples divided in three groups (n=13) randomly. The roughness of each group was evaluated before the bleaching process with Atomic Force Microscopy. Samples was kept in Carbamide peroxide 20%, CP 20% and CPP-ACP ( with 1:1 ratio), CP 20% and CPP-ACP ( with 1:2 ratio) for 14 days, each day 4 hours. The roughness was evaluated two times after bleaching and the results were evaluated statistically. The gained data in each group were evaluated by PAIRED T-Test, and for intra-group analysis ANOVA and POST HOC test was used.
Results: Surface enamel roughness before bleaching was same in all three groups.(p<0.4)The surface roughness after bleaching was increased in Carbamide peroxide 20% and decreased in group 1, significantly  The increase was significant in first group (p=0.01), the decrease was not significant in second group, but significant in third group. (p=0.01)
Conclusion: The 20% CP and CPP-ACP with 1:2 ratio can significantly decrease the surface roughness in comparison to the primary roughness.