Objective To explore the effect of nano -hydroxyapatite（nano -HA） solution and hydrogen peroxide（HP） solution on the enamel surface. Methods Seventy-two bovine enamel blocks were randomly divided into six groups: Deionized water（DW） group, HP+DW group, nano-HA+HP group, nano-HA+HP mixed group, HP+nano-HA group, nano-HA+DW group. Before and after the experiment, the samples were subsequently evaluated by microhardness tester through scanning electron microscope, atomic force microscope and X-ray diffraction. Results After the treatment, significant microhardness loss and morphological change of enamel and decreased crystallinity can be observed in HP+DW group, in the nano-HA+HP group or nano-HA+HP mixed group or HP+nano-HA group, enamel surface become smooth, microhardness increased significantly than the HP+DW group and the crystallinity bounced. Conclusion HP solution can lead to significant morphology change of the enamel surface, hardness loss and crystallinity decreased. The solution of nano-HA and HP, especially the mixed solution can significantly decrease the morphology change of the enamel surface, the microhardness and crystallinity.
