Objective:To determine the enamel surface structure and hardness of the extracted teeth after bleached with three kinds of peroxide bleaching agent:30% hydrogen peroxide(HP),22% carbamide peroxide(result peroxide,CP)and 3% boric acid(sodium perborate,SP)commonly used in clinics.Methods:Specimens of the extracted teeth were randomly divided into four groups(ABCD)which were treated with normal saline,30% hydrogen peroxide,22% had carbamide peroxide and 3% boric acid sodium respectively.Then the teeth were obs...