Caries is one of the most common diseases. It is a chronic, progressive, destructive disease of the hard tissues of the teeth that occurs under the action of several factors. It has the highest prevalence among all kinds of diseases suffered by human beings. It is widespread and dangerous. It can affect the elderly and children to varying degrees. The disease destroys the integrity of masticatory organs, reduces the chewing function and hinders digestion. If caries continues to develop, it can cause pulp disease and pain, and further development can cause periapical tissue disease, osteomyelitis and a series of complications, which seriously affect the whole body health. In childhood, it can affect the growth and development of dental and jaw system and cause the acquired deformity of jaw and face. The incidence of caries in our children is very high, and the incidence rate of our children and adolescents is as high as 40%~50%. Among them, 80%~90% are sulcus caries. A typical molar sulcus can reach 1.5mm in depth, and the diameter of the sulcus is only 0.5mm, so it is easy to hide food residue and bacteria in such deep sulcus, and the toothbrush bristles can only reach 0.4mm. It is difficult to clean the sulcus by brushing and rinsing, so it will be easy to have caries in the enamel and/or dentin around the sulcus of teeth, forming sulcus caries. Especially the “sixth age tooth” is common. Sixth-aged teeth are the first permanent molars that erupt at the age of 5~6 years old in preschool, with a total of 4 teeth, carrying half of the chewing function of human. Their health is beneficial to the growth and development of children’s teeth, maintaining intermaxillary height and preventing the occurrence of malocclusion. However, this tooth erupts shortly with little wear, and the sulcus of the tooth surface is deep and narrow, which is very easy to induce sulcus caries. Therefore, it is important to effectively preserve the first permanent molar to avoid the occurrence of caries. PFS is a method recommended by the World Health Organization (WHO) to children all over the world to protect the milk molars and new permanent teeth. PFS has been used in clinical practice for more than 40 years since the 1960s. It is coated with a polymer material on the surface of milk molar or newborn molar to form a protective layer to close up the sulcus, and after the material hardens, it can be retained in the sulcus point gap for a long time to prevent the occurrence of sulcus caries by isolating food and bacteria from entering the sulcus. The damage caused by caries to people’s health is immeasurable. The treatment of caries is time-consuming and costly, so it is very important to carry out the prevention work of caries. At present, in the prevention of caries in children and adolescents, we usually take the following measures: guiding children and adolescents to adopt oral health care methods such as effective and correct brushing and adopting various means such as fluoride ion introduction and fluoridation of water sources to ensure their dental health. Of course, the gutter closure will certainly improve the anti-carious power of children’s teeth. This method is one of the most important means of caries prevention for children. It is an effective method of caries prevention because it is painless for children, simple and quick to operate, so it is much more acceptable than dental treatment after caries, and the cost is not high. The caries prevention effect of the sulcus closure is sure, as long as the sealant coating film is preserved intact, it can adequately prevent caries. In the areas where it is widely carried out in China, the occurrence of fossa caries is reduced substantially. Vulval closure can achieve good effect with very small human and material resources, and it should be continuously promoted to be widely carried out in all areas with conditions to promote children’s dental health in China. There are some drawbacks of the sulcus closure, that is, the sulcus sealant is not wear-resistant, the retention of the coating film needs to be improved, and it requires very strict cleaning and moisture isolation technology, because most of the preschool children are not easy to cooperate well in the treatment process, and the number of teeth completely lost after 3 years is more. Therefore, it is generally recommended that children should be re-examined once every six months to improve the effect of caries prevention after the closure of the sulcus. But there is no need to make the sulcus sealant never come off for a lifetime, as the age grows, chewing wears out, the tooth tip becomes shorter, the sulcus becomes shallower, and has passed the period of good incidence of caries, which plays the role of protecting teeth. With the improvement of living standard and the change of diet structure, the age of occurrence of first molar caries has the tendency to advance, therefore, closely observe the eruption of first molar and seize the opportunity to carry out sulcus closure on first molar is an effective method to prevent the caries of first molar. It is recommended to seal the sulcus of occlusal surface first, and after the crown of molar is fully erupted, the buccolingual point gap is closed. To sum up, sulcus closure is a painless, harmless, non-invasive and effective method to prevent the caries of milk molar and young permanent molar, which has great clinical significance and social benefits.