This in vitro study was to evaluate the influence of tooth whitening agents (15% carbamide peroxide, 20% carbamide peroxide and 45% carbamide peroxide) on enamel microhardness and the effect of CPP-ACFP on bleached enamel. Materials and method: Thirty enamel specimens were obtained from human third molars and baseline Vickers's hardness was recorded under 100g load during 10 seconds.