Tooth decay, commonly known as “tooth decay”, “worm tooth”, is one of the most common diseases in the oral cavity, which is common in any age, especially in children, and it is a kind of disease that causes the destruction of hard tissue of teeth. If not treated in time, cavity will be formed, and the cavity will not heal by itself, which will eventually lead to tooth loss. At present, the World Health Organization has listed dental caries as the third disease that the world focuses on preventing after cardiovascular disease and cancer. Experts say that because of the prevalence and commonness of tooth decay, many people think that it is just a bad hole in the tooth and it does not affect the health. Especially for the caries of children before tooth replacement, parents think it is not important because new teeth will grow out after tooth replacement. In fact, these perceptions are wrong. If tooth decay is not treated in time, it has very serious harm to anyone. The danger of adult tooth decay: 1.pain. Tooth decay will cause severe pain when the tooth pulp is damaged. 2.Secondary infection. Dental caries is a bacterial infection, if not treated in time, it can lead to pulp disease and periapical disease, and even jaw bone osteomyelitis. It can also act as oral lesion and lead to systemic diseases, such as nephritis, heart disease, etc. 3.Affect digestion and absorption. After tooth decay, the chewing function is reduced, which will affect the digestion and absorption of food. 4.Damage the oral mucosa. After tooth decay, the broken crown is easy to damage the local oral mucous membrane tissue and cause oral ulcer. 5.Tooth loss. When the whole crown is decayed, it cannot be repaired, and can only be extracted. Tooth decay is an important reason for adult tooth loss. The harm of children’s tooth decay: 1.Children’s tooth decay has the same harm as adults. 2.Increase the risk of tooth decay of permanent teeth. The food residue in the cavity and the bacteria will gather and deteriorate the oral environment, which will greatly increase the risk of tooth decay of permanent teeth. 3.Affect the eruption of permanent teeth. After periapical inflammation of tooth decay, it will affect the permanent tooth embryo and lead to the obstacle of enamel development, which will affect the normal eruption of permanent teeth. 4.Cause the permanent teeth are not aligned. If the baby teeth are missing due to caries, it will cause the gap between permanent teeth to be narrowed, and it is easy to occur the misshapen jaw. 5.Psychological influence. When multiple teeth caries occurs, it will affect the correct pronunciation and jaw and facial beauty, and cause some psychological burden to children.