1.Socket caries affects children’s dental health The uneven recessed part of the occlusal surface of the back teeth is called the socket, which is the defect formed by the cusp fusion obstacle during the development of teeth. The sulcus of each tooth has different shapes and depths, which is a suitable place for bacteria to grow and reproduce. In this calm and hidden environment, the bacteria use the sugar (carbohydrate) in the food to reproduce and grow, and produce acid in the process of metabolism to corrode the teeth and form cavities, therefore, the risk of caries is higher in the deep sulcus. At the same time, the bottom of the sulcus is close to the boundary of enamel dentin or located in the dentin, once the caries occurs, the damage can develop rapidly to the deep, forming the cavity which is small in appearance but deep and big in reality, and this kind of caries is called sulcus caries in medical science. The caries can also spread to the pulp (dental nerve) and lead to pulp inflammation or apical inflammation, which will lead to tooth loss if not treated in time. The back teeth are responsible for the main chewing function, once lost, the chewing function will be greatly reduced, affecting the nutritional intake and growth and development. Research shows that among children and adolescents in China, 80-90% of the posterior teeth have sulcus caries, if the occurrence of sulcus caries can be effectively prevented and controlled, it can not only greatly reduce the level of caries in children and adolescents, but also reduce the personal economic burden and social medical resources consumption. 2.Socket closure is an effective method to prevent children’s sulcus caries. Sulcus closure refers to the method of preventing sulcus caries by applying the sealing material to the sulcus point gap on the occlusal surface and buccal and lingual surfaces of the crown without damaging the tooth body tissue to prevent the erosion of cariogenic bacteria and acidic metabolites to the tooth body. The principle is that the liquid resin cures and hardens after entering the sulcus, forming a protective barrier that covers the sulcus and prevents the cariogenic bacteria from entering, thus achieving the purpose of preventing sulcus caries. This is just like in daily life, to prevent wood products from corrosion and insect decay, a layer of paint is applied on the surface, and to prevent iron products from rusting, anti-rust paint or spray plastic is applied. This resin is non-toxic and harmless, and does not affect the chewing function of people, but also can adapt to the environment of the mouth. Vulcan sealant is an effective method to prevent children’s sulcus caries. As long as the vulcan sealant remains intact on the tooth surface, it can effectively protect our teeth. Even if the sealant falls off, the resin protrusion that penetrates into the enamel has a certain protective effect on the teeth. The main application of the sealant is on the milk molars, permanent molars and permanent premolars. The best time to seal is when the crown is fully erupted and the caries has not yet occurred, generally at the age of 3-5 years for the milk molar, 6-8 years for the first permanent molar and 11-13 years for the second permanent molar. Young people with deep sulcus can also have sulcus closure to prevent caries, but the sulcus of middle-aged and old people’s back teeth will gradually become shallow or disappear with the abrasion of chewing food, and some of them have already got caries after the susceptible period of sulcus caries, so it is not necessary to do sulcus closure again. 3.Safety and simplicity of the operation of the fossa closure Fossa closure is a painless, non-invasive, safe and simple caries prevention technology. The sealing material used is non-toxic and harmless to the teeth, even if the sealing material falls off and is swallowed, there is no adverse effect on human health. Children who receive the sealant do not feel any discomfort in the process of sealant, and the whole process is divided into 6 steps, which only takes about 10 minutes: a. Cleaning. Remove food debris and plaque from the dental surface. b. Acid etching. Treatment of the tooth surface with weak acid, to re-clean and facilitate the role of sealant adhesion. c. Rinsing and drying. Rinse the weak acid left on the tooth surface and blow dry the tooth surface in a chalky state. d. Application of sealant. Apply the sealant sequentially at the sulcus. e. Curing. The sealer is cured and hardened by visible light for about half a minute. f.Check. Check the sealing effect. The sealant can be maintained on the tooth for several years. Just closed teeth, avoid biting too hard and sticky food, such as chewing gum, bubble gum. After the closure, it is best to review once after 3-6 months, and then every year when the oral routine examination, at the same time check the closed teeth, if the sealant is found to fall off, timely to make up. 4.The joint use of the fluoride and the sulcus closure can prevent the occurrence of caries to the greatest extent. Caries can occur in different parts of the teeth, and the caries that occurs in the part of the sulcus is called sulcus caries, and the caries that occurs in the smooth surface is called smooth surface caries. The use of sulcus closure can prevent the occurrence of sulcus caries, but it has no prevention effect on the smooth surface and adjacent surface of teeth. Fluoride is a chemical caries prevention method, which can effectively prevent the occurrence of caries on smooth surface and adjacent surface of teeth by enhancing the anti-carious ability of teeth and promoting remineralization. Therefore, the combination of sulcus closure and fluoride can prevent both sulcus caries and smooth surface caries, and prevent the occurrence of caries to the maximum extent.