The causes of dental caries include bacterial factors, dietary factors, the tooth's own factors, and time factors, also known as the four-factor theory of dental caries. Dental caries initially result from bacterial infection. Under such infections, the hard tissues of the tooth undergo a chronic destructive deterioration; over time, this results in cavity formation. That is to say, the formation of dental caries primarily occurs under bacterial infection. Additionally, diet is a main cause of dental caries, especially sugary foods. Bacteria use glucose to produce acid, leading to tooth demineralization and cavity formation. Moreover, congenital calcium deficiency in teeth, leading to incomplete enamel development, is also an important cause of dental caries. Furthermore, the formation of dental caries requires a certain time factor.