Tooth decay, commonly known as worm teeth and tooth decay, is one of the most common diseases of human beings, and many people do not take it seriously, but they do not know that simple tooth decay can cause big problems, and the World Health Organization has listed it as one of the three major diseases of human beings, together with tumor and cardiovascular disease. Here we will talk about the danger of dental caries to adults and children respectively. 1.The danger of tooth decay to adults (1) When the tooth decay is serious, the food cannot be chewed, and the food is swallowed before it is fully ground, which increases the burden of gastrointestinal tract, especially for the elderly, the digestive ability of gastrointestinal tract has been weakened, which will lead to insufficient nutrition intake and is not good for the health. (2) The early caries is usually not felt, but the cavity deepens continuously, the bacteria inside and the toxin produced by the bacteria infect the pulp and pulpitis occurs, then there is severe pain. It makes people restless and unable to sleep, this is what people often say “toothache is not a disease, but pain really kills”. (3) If pulpitis continues to develop, it will cause the inflammation of the apical part of the tooth and local swelling when it is serious; if the pus and bacteria are absorbed, it may cause sepsis or bacteraemia, and even threaten the life. 2.The harm of tooth decay to children There are many parents think that children need to change teeth, and the tooth decay of milk teeth can not need treatment, in fact, this concept is very wrong, the harm of children’s tooth decay mainly has the following aspects. (1) Tooth loss, involving more than one milk molar, can reduce the chewing function, causing insufficient nutrition and affecting the growth and development of children. (2) The food residue stays in the cavity, and the bacteria gather, so that the oral hygiene deteriorates and other teeth are more prone to caries, including the newly replaced permanent teeth. (3) If the caries of milk teeth is serious, it will affect the permanent teeth that have not yet erupted below, hinder or delay the permanent teeth, and may also cause the abnormal development of permanent teeth. (4) The premature loss of the baby tooth due to caries will cause the neighboring baby teeth to shift and the gap to shrink, which cannot leave enough space for the permanent teeth and cause the abnormal position of the permanent teeth in the future. (5) The edge of the cavity is too sharp, and it is easy to cut the tongue and mucous membrane. (6) Severe caries causes the inflammation of tooth root, and the bacteria and pus in it will cause the infection of other tissues of the body. (7) It affects the aesthetics and correct pronunciation, and also causes some influence to the psychology of children. Therefore, it is very important to do prevention or early treatment.