During the period of mixed dentition, as the permanent teeth gradually erupt, the caries rate of permanent teeth gradually increases, especially the first permanent molar erupts earliest and the caries occurs early. The young permanent teeth in the period of mixed dentition are often mistaken as milk teeth by parents, so they should do a good job of caries prevention: 1. “Brush inside and outside”, but also pay attention to brush the occlusal surface of the back teeth, so that you can brush the food residues between the teeth and each tooth surface, do not brush horizontally, horizontal brushing is easy to damage the gums, but also can not brush the food residues between the teeth. Do brush your teeth in the morning and evening, and rinse your mouth after meals. It is even more important to brush your teeth before going to bed, because the interval at night is long and bacteria are prone to multiply. 2.Reduce or control sugar in the diet Attention should be paid to propaganda so that parents educate children to develop the habit of eating less snacks and candy pastries, not to eat sugar before bedtime, pay attention to the quality of children’s three meals a day, and develop from childhood to eat more vegetables, fruits and foods containing calcium, phosphorus and vitamins, etc., and to eat as much coarse food as possible. 3.The use of fluoride Fluorine has an important role in the prevention of dental caries, including promoting the remineralization of enamel, enhancing the ability of enamel to resist demineralization and reducing the acidic products in plaque. Commonly used fluoride methods include: tap water fluoridation, school water fluoridation, dental surface fluoride coating, fluoride toothpaste brushing, fluoride solution mouth rinsing, etc. Application of sulcus sealant Sealant is used to seal the caries-prone parts such as the coincidental sulcus and the buccolingual sulcus of permanent molars, which can play a good role in preventing caries, especially the “six-year-old teeth” erupt early and have a high caries rate, so the caries prevention work should be done early.