The chewing surface of children’s milk molar and permanent bicuspid and permanent molar (commonly known as “back groove teeth”) is uneven, there are some natural sulcus and fissure, plaque and food residue are easy to accumulate in these parts, and it is also hard to remove them by brushing teeth, after a long time, caries will occur in the sulcus part, i.e. sulcus caries. According to our statistics, the chance of children’s first and second permanent molar caries is more than 50 times higher than that of front teeth, and 90% of the first and second permanent molar caries are sulcus caries. The reason is many, one is because the newly erupted teeth are not fully developed, the surface layer is not calcified enough, and the acid resistance is poor, so it is easy to occur caries. Secondly, because children are poor in self-awareness, it is difficult to insist on using the correct brushing method twice a day in the morning and evening to thoroughly remove the plaque and food residue from the tooth surface, and children like to eat sweet food and candy and pastry. Thirdly, parents often ignore the eruption of permanent molars during children’s tooth replacement period, mistaking them for milk teeth, and do not treat them in time when caries is found. For the above reasons, the caries of permanent molar in children is very common, and sometimes the caries is very serious. Therefore, the prevention of sulcus caries will greatly reduce the incidence of caries in permanent teeth of children and adolescents, and thus improve the oral health level. The most effective way to prevent sulcus caries is to use the method of sulcus closure, which has been widely used in the world. The principle is very simple, which is to fill the fossa and sulcus of the molar chewing surface with a polymer resin material to isolate the external caries-causing factors and achieve the purpose of caries prevention. So, who are the children suitable for the closure? Generally speaking, the best results are achieved within 1 year after the eruption of molar teeth. Because the surface layer of newly erupted teeth is not sufficiently calcified, the acid resistance is poor, and caries easily occurs, so preventive measures should be taken as early as possible; on the other hand, the surface grooves of newly erupted teeth are deep, and the sealant is not easy to fall off, so the effect of caries prevention is the best. Specifically, sulcus closure is suitable for children in the following cases: children aged 3-4 years old, seal the milk molar. The milk molar teeth erupt around 3 years old and are replaced only around 11-12 years old, which stay in the mouth for a long time and have an important role, so if conditions are available, they should be sulcus closed. However, due to the young age of children, they are not very cooperative, so it is difficult to close the sockets of molars. Children aged 6-8 years old to close the first permanent molar, the first permanent molar (six-year-old teeth) eruption time is about 6 years old, is the earliest eruption of permanent teeth in the oral cavity, but also to play a chewing function, affect the alignment of teeth, affect the jaw and facial development of the extremely important four teeth (upper, lower, left, right each 1), must be focused on protection. Parents are reminded that the teeth must be completely erupted out of the oral cavity without gum (flesh) coverage before the sulcus closure can be done, otherwise the sealant will easily fall off due to the influence of the gum gum sulcus liquid and cannot achieve the purpose of caries prevention. 11-13 years old children with bicuspid teeth and second permanent molar just erupted have the best effect of sulcus closure. For children in other age groups, it depends on clinical examination and past medical history. For example, if the molar sulcus in the mouth of a child is deep, or there are many other teeth with caries, or if the child has a lot of decayed milk teeth, or has poor oral hygiene habits such as eating sweets and not brushing teeth carefully, such children must have sulcus closure after the eruption of the first and second permanent molars. For children with disabilities who have poor oral hygiene, although they are older or have teeth erupted for a longer period of time, they can also consider appropriately relaxing the age of fossa closure. After the closure, you should go to the hospital for inspection once every six months, as long as the sealant can exist intact, it can play the role of caries prevention. If the sealing material falls off, it should be re-sealed and checked regularly.