There are many factors that cause tooth discoloration, mainly the following: dental fluorosis, also known as dental fluorosis or mottled enamel teeth. The disease has the characteristics of regional onset, mainly due to the high fluorine content in drinking water. The enamel on the tooth surface is opaque and chalky; In moderate cases, the tooth surface is yellow or brown with irregular patches; In severe cases, there are not only color changes, but also enamel defects. Enamel hypoplasia is the lack of calcium, phosphorus, vitamins A and D in surface enamel during tooth development. Or tooth development disorder caused by harmful factors. The enamel on the light tooth surface is opaque chalk, loose and rough, and can be yellow-brown due to food staining. In severe cases, the enamel on the tooth surface may have substantial defects, which are nested or banded, or even not covered with enamel. Tetracycline teeth, especially children under 8 years old or pregnant women, can easily cause tooth discoloration if they take tetracycline drugs (such as tetracycline, oxytetracycline, doxycycline, etc.). ), also known as tetracycline teeth. This is because tetracycline drugs can combine with calcium ions in tooth tissue to form stable tetracycline calcium salt, and the discoloration will gradually increase with age, and it will tend to be stable after 18 years old. According to the depth of coloring, the clinic can be divided into four degrees. At one time, the tooth surface of tetracycline teeth was even milky yellow or light yellow; The second degree tooth surface is uniform brown or grayish yellow with different shades; The third degree tooth surface is uniform pure gray, taupe or grayish black with different shades; Fourth, the tooth surface is grayish brown or grayish black, which may be accompanied by enamel hypoplasia and tooth tissue defect. Koga's disease of breast is a rare autosomal dominant genetic disease. The affected teeth have unique purple-blue changes, the exposed dentin is bright and translucent yellow-brown, and the teeth are easy to wear, and in severe cases, they are residual roots. Dental caries, commonly known as worm teeth or tooth decay, is due to the acidolysis of sugar food with the participation of bacteria, which corrodes teeth, softens teeth, and tooth tissue disintegrates over time, forming a black cavity. Dead pulp discolored teeth are often discolored by deep caries bacterial infection or direct violence, and the teeth are accidentally broken, resulting in pulp injury and necrosis.