First, the sulcus caries affects the dental health of children. The sunken part of the occlusal surface of the back teeth is called the sulcus, which is the defect formed by the obstacle of tooth cusp fusion 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 percent of posterior teeth have sulcus caries, if we can effectively prevent and control the occurrence of sulcus caries, we can greatly reduce the level of caries in children and adolescents, and also reduce the personal economic burden and social medical resources consumption. Secondly, fossa closure is an effective method to prevent children’s fossa caries. The method of preventing sulcus caries is to apply the sealing material to the sulcus point gap on the occlusal surface and buccal and lingual surface of the crown without damaging the tooth 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. 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 there is no need to do sulcus closure again. Thirdly, the operation of fossa closure is safe and simple. Fossa closure is a painless, non-invasive, safe and simple caries prevention technique. It uses non-toxic sealing material, which is harmless to teeth, and 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: 1. Removal of food debris and plaque on the dental surface. 2, acid etching. Treatment of the tooth surface with weak acid, to play a re-cleaning and facilitate the role of sealant adhesion. 3.Rinsing and drying. Rinse the weak acid left on the tooth surface and blow dry the tooth surface in a chalky state. 4.Application of sealant. Apply the sealant sequentially at the sulcus. 5.Curing. The sealant cures and hardens by visible light for about half a minute. 6.Check. Check the sealing effect. The sealant can be maintained on the tooth for several years. Just sealed 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. Fourthly, the joint use of fluoride and sulcus sealant can prevent the occurrence of caries to the maximum extent. The caries can occur in different parts of teeth, the caries that occurs in the part of the fissure groove is called sulcus caries, 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 preventive 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.