The crown of a normal tooth is white, with a slight yellowish tinge near the gums, due to the thinner enamel near the outside of the gums, which reveals the light yellow color of the dentin. A set of white and neat teeth will add luster to one’s face. However, there are often some children who have just grown new teeth will appear yellow teeth, black teeth, brush can not brush clean, what is the reason? This is caused by taking tetracycline drugs, which is difficult to treat. In the past, when the child has a fever, tonsillitis, cough take some tetracycline effect is very good, and convenient, so a lot of families have brought their own this medicine. However, many parents do not anticipate the adverse consequences of taking tetracyclines on a regular basis. Tetracycline is a powerful chelating agent that binds firmly to the calcium deposited in the dental tissue. The kidneys of newborns (especially premature babies) are not fully developed, and the excretion of tetracycline taken during this period is slower, and the concentration of tetracycline in the blood is higher and maintained for a longer period of time, thus increasing the chances of tooth staining. Tetracycline staining occurs only during the developmental stage of the teeth, not during the period of tooth eruption. Stained teeth are lighter in color when they first erupt and then gradually darken to a yellow, gray or brown color. Chrysomycin staining is grayish brown, while tetracycline and hyoscine are yellow, with hyoscine staining being lighter. This is the reason why many yellow teeth and black teeth appear. The staining of baby teeth is usually more pronounced than that of permanent teeth, due to the fact that tooth staining occurs mainly in the dentin. The enamel of baby teeth is thinner and the color of the dentin comes through easily. Similarly, permanent incisors are more significantly stained than permanent cuspids. The degree of damage caused by tetracycline to children’s milk and permanent teeth depends on the age at which the tetracycline is taken. The administration of these drugs to women over the fourth month of pregnancy can cause young children’s milk teeth to change to a fluorescent yellowish brown or yellowish gray color, poorly developed enamel, and misshapen and unsmooth teeth. Even short-term use of tetracyclines in young children can cause discoloration and dysplasia of the milk teeth and permanent teeth. The staining of the permanent anterior teeth is associated with the use of medication during the mother’s pregnancy and in young children within 5 years of age. The degree of staining can range from light yellow to dark yellow or dark gray. Generally the higher the dose of the drug, the darker the staining and the more severe the enamel dysplasia and malocclusion. Tetracycline staining occurs only during the calcification period of tooth development. The calcification period of the crown of a baby tooth begins roughly in the fourth month of fetal life and is completed one year after birth. The risk period for tetracycline staining is from the fourth month of fetal life to the third month of life for incisors and from the fifth month of fetal life to the ninth month of life for cuspids. During the calcification period of tooth development, tetracycline can stain the deciduous teeth to varying degrees when administered by the mother (through the placenta) or by the baby. The calcification period of the permanent incisor crown begins roughly at 3 months of age and is completed by 6 years of age, during which time tetracycline tends to stain permanent incisors. The degree of staining varies when the medication is administered at different times in the calcification of the developing tooth. In the early stage of calcification, the coloring zone of dentin is close to the surface of the crown, and the coloring is obvious; in the late stage of calcification, the coloring zone of dentin is far from the surface of the crown, and the coloring is deep in the dentin, and the degree of coloring is light. The stained milk teeth are gradually replaced by permanent teeth from the age of 6. If the permanent teeth are stained, they should be replaced by other appropriate drugs instead of tetracycline. The staining and deformation of teeth caused by tetracycline significantly affects the aesthetics of teeth. However, there is no way to overcome this special effect of tetracycline. So the key is prevention. Tetracyclines are mainly prohibited for pregnant women over 4 months of pregnancy and infants up to 6 years of age, and are replaced by other drugs in case of inflammatory infections. Tetracycline can cause many dental problems therefore in recent years tetracycline has been included in the list of discontinued drugs.