Small pits on the surface of teeth are caused by a variety of reasons, as follows: 1. It may be a precursor of tooth decay. The earliest manifestation of tooth decay is tooth discoloration and lack of luster, followed by pigmentation, and the early manifestation gradually changes from chalky white to yellow, yellow-brown and black. Examination can reveal that the teeth become soft and rough, and the affected teeth usually have no obvious symptoms; 2. It is caused by tooth enamel dysplasia, which is caused by systemic diseases, nutritional disorders, or periapical infection of milk teeth during the development of teeth, resulting in abnormalities of enamel structure, manifested as yellowing and discoloration on the tooth surface. Brown sunken pits of varying sizes or bands are seen, and the teeth occur with symmetry. Examination can be found that the tooth is hard and also relatively smooth; 3, for dental fluorosis, is due to teeth during development, that is, in the fetus, or before the age of 6 years old living in high fluoride area, mostly related to the local water supply, manifested as chalky white or brown, brown plaque-like damage on the tooth surface, the heavy case can be seen enamel defects, even 1/4 of the crown, all of the crown, the surface is also symmetrical, the tooth is hard and smooth, can be found in the same area of the population with similar symptoms.