1.Tooth decay, how is it formed? There are four conditions for the occurrence of dental caries: bacteria, food, teeth, and time. Under normal circumstances, there are many bacteria in people’s mouth, among which one kind of acid-producing bacteria is Streptococcus pyogenes, also called cariogenic bacteria. When the food residue exists on the tooth surface for a long time, the cariogenic bacteria will react with the carbohydrates in the food to produce acid, and these acids will react with the tooth enamel to decalcify, soften and disintegrate the tooth enamel surface, forming a shallow cavity, at this time there is no painful feeling and it is not easy to be noticed. If left untreated at this point, the cavity will become larger and deeper, damaging the superficial layer of dentin, at which point the tooth will feel sore when eating hot, cold, sour or sweet stimulating foods. If it is still ignored, it will damage to the pulp and cause pulpitis, and then there will be spontaneous and severe pain. 2.How to prevent the occurrence of tooth decay? (1) It is most important to develop good oral hygiene habit. Brush your teeth at least twice a day for not less than 3 minutes each time. Use dental floss once a day to clean your teeth, so that the caries-causing condition of food is removed. (2) Use fluoride toothpaste for teeth. Fluoride ions combined with calcium ions in the teeth can enhance the teeth’s ability to resist acid erosion. (3) There are some structural defects in teeth, such as deep sockets, which can be prevented by sulcus closure. In addition, uneven teeth also tend to cause cleaning difficulties, and orthodontics can solve this problem. (4) Regular visits to the dentist for oral examination and scaling, for deep cleaning and protection of teeth. (5) Develop good eating habits, eat more vegetables and fruits, reduce the number of snacks and drink less sugary drinks.