Tooth decay is also called “worm teeth” in common people’s language, and its incidence rate in the population can reach 50%. It not only affects the chewing function of the patient, but also endangers the physical health of the patient, and seriously affects the beauty of the face. The development of serious can also cause systemic diseases and lead to mental disorders of patients. Therefore, the World Health Organization has classified dental caries as a disease of global prevention and control together with cardiovascular disease and malignant tumor. In medical terminology, dental caries is a disease of chronic progressive destruction of hard tissues of teeth. The incidence of dental caries is different in each stage of human growth. The incidence of dental caries is higher in adolescents during the years when the milk teeth and permanent teeth are just erupting; however, after entering adulthood, it will slowly calm down and generally no longer develop; in old age, the incidence of dental caries will increase again to a certain extent. Most of the dental caries appear in the molars, especially the first and third molars of the upper and lower jaw, maxillary incisors and bicuspids. The incidence of cuspids and mandibular incisors is less frequent. The caries can be divided into three types according to the degree of damage to the hard tissues of the teeth: superficial caries: also known as enamel caries, the caries is only limited to the surface of the teeth, the patient usually has no conscious symptoms, and can see the white chalk-like spots in the sulcus or on the surface of the teeth during the examination by the dentist, or the pigmentation forming ink-soaked spots. Medium caries: It can also be called as superficial dentin caries, where the caries is eroded to the superficial layer of dentin. In this case, small dark brown cavities can be seen on the teeth. Because there are dentin tubules inside the dentin, which contains rich nerve endings, it will produce pain when encountering acid, sweet, cold and hot stimulation. Deep caries: It can also be called dentin deep caries, the caries is close to the pulp and forms a deep hole, when encountering acid, sweet, cold and hot, the painful stimulation will be very obvious and seriously affect the patient’s daily life. There is still no clear statement in the medical field about the determinants of tooth decay, but according to our daily assertion, we can roughly think that there are the following aspects. Caries-causing bacteria: Streptococcus pyogenes should be the main caries-causing bacteria, which has strong affinity with tooth enamel on tooth surface and can synthesize insoluble and sticky plaque with sucrose in food to fix on tooth surface, rapidly transforming sugar into acid, leading to decalcification and caries of teeth. In addition, the occurrence of dental caries is closely related to Streptococcus melitensis, Actinomyces and Lactobacillus. Body susceptibility: The occurrence of dental caries is related to the form, arrangement, position and structure of teeth, such as crowded, overlapping and misalignment of teeth, because these teeth are easy to retain food and plaque, which leads to dental caries. Secondly, tooth decay is related to nutritional factors. Because the lack of nutrition can affect the development and mineralization of teeth, thus can increase the susceptibility of the body. According to what we know now, calcium, phosphorus, protein, vitamin ABCD, fluorine and some other trace elements have a close relationship with dental caries. In addition, caries is also related to endocrine and genetic factors, for example, hyperthyroidism and diabetes are more likely to suffer from caries. Oral saliva: Dental caries is related to oral saliva, such as oral saliva, if the amount of saliva secreted by oral saliva is small, thick and acidic, it is easy to suffer from dental caries. At the same time, saliva contains lysozyme, immunoglobulin and leukocyte, they have bactericidal effect, and the amount of its content also has a certain relationship with the occurrence of dental caries. Drinking water: In the natural environment, the level of fluoride in local drinking water is closely related to dental caries and fluorosis. If the fluorine content in drinking water is low, tooth decay will occur easily; on the contrary, if the fluorine content in drinking water is high, dental fluorosis will occur easily. Treatment and prevention of dental caries For early treatment of dental caries, not only the damage to dental tissue is less, the pain of patients is less, but also can effectively curb the aggravation of dental caries, so that patients can avoid the pain of pulpitis and periapical class. Therefore, it is necessary to insist on regular check-ups, and strive to achieve timely detection and early treatment of the disease. The treatment of shallow caries is relatively simple and easy. Because the self-repairing ability of caries is very poor, so early filling is especially important. It can stop the further development of dental caries, if we find out we have the first caries in the sulcus, we should go to the dentist immediately to grind out the decayed tissue. For tooth decay, besides early detection and timely treatment, I think prevention is more important. In our daily life, the following aspects can play an effective role in prevention: strengthen the supply of calcium, phosphorus, vitamins and trace elements to enhance the body’s ability to prevent caries. At the same time, avoid taking tetracycline drugs during the school life. Remove dental plaque timely, keep oral hygiene and eliminate caries-causing factors. Pay attention to control the intake of sugar and refined carbohydrates in normal life, consume more coarse fiber food, insist on brushing teeth in the morning and evening, and rinse mouth against meals. The correct method of brushing teeth is an important method to maintain oral hygiene. How to brush teeth correctly, medical experts believe that the effective method of brushing teeth is “3, 3, 3” system, that is: brush teeth within 3 minutes after each meal, brush teeth 3 times a day, brush teeth for 3 minutes each time. Brushing should be done in the direction of tooth growth, with the upper teeth brushed from top to bottom and the lower teeth brushed from bottom to top, so that the bristles rotate up and down gently parallel to the tooth axis. The temperature of water for brushing should be preferably 35~36.5℃. Use fluoride to reduce caries. Fluoride can be rubbed on the tooth surface by the dentist, or toothpaste containing fluoride can be used to enhance the anti-caries ability.