Teeth are composed of enamel, dentin, bone and pulp. The dentin is the main body of the tooth, and the enamel covers the surface of the crown. The enamel is translucent and its color is related to the degree of mineralization of the enamel, its thickness, and the color of the dentin beneath it. Dentin is pale yellow and opaque. The color of normal teeth is mainly the dentin color that appears through the enamel. The color of dentin deepens in older people and can be brownish-yellow, the more mineralized the enamel, the more transparent it is. The yellow color of dentin through the teeth is light yellow, the lower the degree of mineralization, then the enamel transparency is poor. The dentin color does not transmit easily, and the teeth appear milky white. Some people do not pay attention to oral hygiene and do not brush their teeth effectively in the morning and evening, so that the surface of the teeth accumulates a layer of food debris, soft tartar, tartar, tobacco stains, tea stains, etc. These yellow teeth are not the color of the teeth themselves. There is also a case of tetracycline teeth, the patient took tetracycline drugs during the period of tooth development and mineralization, so that the color and structure of the teeth changed the disease, often brown or brown, yellowish brown.