Dental caries forms under the combined effect of bacteria, diet, environment and time. 1. Bacteria: Bacteria is the main factor for the occurrence of caries, due to the acid-producing power of Streptococcus mutans and Actinobacteria are relatively strong, which can cause local demineralization of dentin and lead to the formation of caries. 2. Diet: Eating sugary food, sugar can be retained in the gap in the teeth, bacteria use sugar metabolism to produce organic acids can cause demineralization of tooth enamel, thus leading to the formation of caries. 3. Environment: saliva is the external environment of the teeth, its quality and quantity changes, changes in the antibacterial system and buffer capacity are closely related to the development of dental caries. 4. Time: the formation of dental caries is generally a very slow process. When carbohydrates are retained on the tooth surface, it affects the time of tooth eruption, which leads to the formation of plaque and the formation of dental caries. The formation of cavities generally need 1 to 2 years of time, the occurrence of dental caries is often bacteria, diet, environment and time and other reasons to participate in the formation of the results.