Abstract: Objective To observe the effect of tooth-whitening products on the hardness of demineralized and stained teeth after orthodontic treatment. 
Methods In total,120 premolars extracted due to orthodontic treatment were used to establish early demineralization models. They were randomly divided into four groups(n=30): Opalescence tooth-whitening products group(group A), beyond tooth-whitening products group(group B), duraphat group(group C), and blank control group(group D). The changes in color scale and enamel microhardness were estimated. 
Results ①Colorimetric palette: The color scale values of each group gradually decreased and then increased with time, and the difference in color scale values in time points between groups was statistically significant(P＜0.05). ②Surface microhardness value(SMV): The change of SMV value of group A showed a trend of initial increasing and then decreasing with time, and SMV values in the other three groups increased initially with time and then tended to be stable. Comparison between groups showed that except the absence of statistical differences between group A and group C, the difference between the remaining groups was statistically significant(P＜0.05). 
Conclusion Opalescence Boost teeth-whitening products and beyond teeth-whitening products can remineralize the demineralized teeth.Opalescence Boost teeth-whitening products have a slightly higher degree of enamel mineralization than Beyond teeth-whitening products.

Key words: dental enamel, enamel demineralization, tooth-whitening