Fluorine is one of the essential trace elements, it is involved in the calcification and development of human bones and teeth, so the right amount of fluorine is beneficial to the body, especially dental health. About 70% of human fluorine sources come from drinking water, and a large number of studies have confirmed that a water fluoride concentration of 0.7 ~ 1 ppm is the appropriate water fluoride concentration. At present, 24 countries in the world have adopted artificial water fluoridation; it has made great achievements in the prevention of dental caries; however, water fluoridation is a very precise and complicated scientific project, and if you are not careful, the excessive water fluoride concentration will cause tooth dysplasia, enamel yellowing and defects; fluorosis. In recent years, many kinds of local fluorine caries prevention preparations have been introduced in China, and the effect of preventing caries is very remarkable through clinical application. The main preparations are: fluorine protective agent, fluorine foam, silver diamine fluoride, etc.; operation process: 1.Clean the tooth surface: remove the tartar and dental bacteria on the tooth surface with a small brush and special detergent. 2.Blow dry the tooth surface. 3.Apply the fluorine anti-caries agent. Don’t drink water for half an hour after applying fluoride, and eat after two hours; in general, apply once a week, three times in total. These methods must be carried out by a dentist. The fluoride toothpaste suitable for personal self-care can be used, because the fluoride content in different types of fluoride toothpaste is different, there are two kinds of fluoride toothpaste for adults and children in the market; it should be noted that children should use the fluoride toothpaste for children; children under three years old can easily swallow the toothpaste because the swallowing reflex mechanism is not yet complete, which will cause the toxic side effect of fluorine accumulation in the long run.