The dangers of excessive fluorine application or uncontrolled use of fluorine at home are as follows: 1, excessive use will form fluorosis, fluorosis can cause nausea, vomiting and other symptoms, causing systemic diseases; 2, some high fluorine areas can not use fluorine, easy to form dental fluorosis; 3, some children are allergic to fluorine can not be coated with fluorine. The above is part of the precautions, must go to the regular hospital regular coating, play a positive role in caries prevention. Fluoride coating of teeth in children’s mouth is a very good care method for local application, which can strengthen tooth enamel, clean mouth, reduce oral bacteria, have the effect of mineralizing teeth, and is a new type of trace element. However, there are certain precautions for fluoride application, i.e., it should not be overdosed. Its toxic amount is 5mg per kilogram of body weight. In regular hospitals, fluoride is applied with fluoride gel and liquid fluoride; fluoride gel is the size of a pea and liquid fluoride is about two drops. The time of fluoride application is usually 2-3 months, and the number of fluoride application is decided according to the degree of caries and the number of caries detecting bacteria. It should be noted that the safe dose must be mastered in the hospital.