Abstract: Objective To evaluate the therapeutic effect of penetrating resin on bleached early enamel caries.Methods A total of 135 cattle incisors were immersed in the demineralization fluid for 24 h. After the formation of chalk stains, they were randomly divided into 3 groups (n=45): the bleaching group (bleached with 40% hydrogen peroxide), the infiltration group (treated with infiltrated resin) and the bleaching and permeation group (bleached with 40% hydrogen peroxide and then treated with an infiltrated resin). All samples were pH-cycled for 28 d to simulate oral conditions. The color and surface microhardness (SMH) and surface microhardness recovery (SMHR) of the enamel were determined before and after the lesion. Three sets of color changes [ΔE (post-disease-basic value), ΔE (post-experimental-basic value) and ΔE (post -experimental-post-loss)] and surface microhardness recovery rate were calculated, and osmotic evaluation was performed using scanning electron microscopy. Results There were no significant differences in SMH before and after the lesion formation between the three groups. After the experiment, the SMH and SMHR were in the infiltration group>bleaching infiltration group>bleaching group (P＜0.05). There were significant differences in ΔE (post-experimental-basal value) and ΔE (post-experimental-post-loss) between the infiltration group and the bleaching group (P＜0.05). The whitening effect was higher in bleaching group than that of infiltration group, but still significantly worse than that of bleaching infiltration group.Under the scanning electron microscope, it can be seen that the bleaching and permeating group has relatively uniform resin penetration, and there were different ultrastructures between the cured resin materials. Conclusion The bleaching treatment before resin penetration can effectively improve the microhardness and the whitening effect.

Key words: dental enamel, penetrating resin, tooth bleaching, white spot lesion, microhardness recovery rate