Fluoride application in children is carried out once in 6 months-1 year. After coating the enamel surface of milk teeth and permanent teeth with fluorine-containing drugs such as sodium fluoride and stannous fluoride, it can promote enamel remineralization, block enamel pores, enhance enamel corrosion resistance, and effectively prevent caries from occurring. Frequent application of fluoride, not only can not improve the hardness of enamel, but also may cause children to swallow by mistake, etc., with the risk of fluorosis. Fluoride-containing drugs continue to act for 6 months to 1 year, and then the enamel pore space gradually opens up, requiring fluoride application again.