The first permanent molars are the first permanent teeth to erupt in the oral cavity, and they are also the four teeth that are extremely important for chewing function, tooth arrangement and jaw and face development. The surface of the newly erupted molars has many grooves, which are uneven and deep, easy to accumulate caries-causing bacteria and food residues, and not easy to remove, once the bacteria invade and multiply, it can gradually damage the whole tooth, so we must focus on protecting the sixth-aged teeth. It can penetrate into the sulcus on the surface of teeth in liquid state and become hard after light, which is like putting on a protective coat for teeth to prevent bacteria and food residue from entering the sulcus, and at the same time, the original bacteria in the sulcus will die gradually due to the cut off of nutrition, so that the enamel can be protected from bacteria and metabolic products. This can protect the enamel from the erosion of bacteria and metabolic products, enhance the anti-caries ability of teeth, and can most effectively prevent the occurrence of sulcus caries. The first permanent molar generally starts to erupt at the age of 6-7 years old, and the best time to close it is at the age of 7-8 years old, that is, the earlier the teeth are closed after they have completely erupted, the better. The method of the treatment of sulcus closure is very simple, which can be completed by several steps of cleaning the teeth – acid etching – rinsing and drying – applying sealant – curing. If children are cooperative, the four upper and lower left and right teeth can be done in one visit, taking only 20 minutes. Because there is no need to drill the teeth, it is painless and easy for children to accept, and it is the most effective method to prevent sulcus caries at present.