Fossa sealing refers to the method of preventing fossa caries by applying fossa sealing material to the fossa pitting on the occlusal and buccolingual surfaces of the crowns of the teeth without damaging the dental tissues, when it flows into and penetrates the fossa it cures and hardens to form a protective barrier covering the fossa, which is capable of preventing caries-causing bacteria and acidic metabolites from attacking the dentin. Fissure sealing is a painless and non-invasive method, and the technique has been used internationally for more than 50 years. The best time for fissure sealing is when the teeth are fully erupted and caries has not yet occurred. 1, children’s teeth erupt to reach the occlusal plane that is suitable for fossa closure, generally within 4 years of eruption. 2.Milk molar 3-4 years old, the first permanent molar 6-7 years old, the second permanent molar 11-13 years old, bicuspid teeth 9-13 years old. 3, for children with disabilities with poor oral hygiene, although older or teeth erupted from the mouth for a longer time, can consider relaxing the age of fossa sealing.