Endogenous pigmentation caused by taking tetracycline group drugs, such as tetracycline and hyoscine, during the period of tooth development, which turns the teeth yellowish gray, is called tetracycline-stained teeth. Many studies believe that, after taking tetracycline drugs, about 10% can not be discharged, mainly deposited in the bone and teeth, the teeth are mainly deposited in the dentin, less in the enamel, the deposit is a tetracycline orthophosphate calcium complex, and with a light yellow fluorescence, in the sun under the action of ultraviolet light, gradually from yellow to brown or brownish gray, the greater the amount of drug discoloration, the longer the drug The more the dosage, the heavier the discoloration, and the longer the dosage, the more extensive the discoloration of the crown. Clinical manifestations: Patients have a past history of taking tetracycline drugs during infancy or during their maternal pregnancy. The entire mouth shows uniform yellow and gray changes, and the affected teeth show fluorescence under ultraviolet light, which can be classified according to the degree of discoloration: Mild: light yellow, light gray. Moderate: yellowish-brown. Severe: brown, gray-brown. The teeth are generally normal in appearance, hard and smooth, sometimes combined with enamel hypoplasia. At present, there is no ideal decolorization method to treat tetracycline-stained teeth. Only moderate and mild cases can be treated by decolorization method. For severe cases, composite resin veneers, porcelain veneers, metal porcelain crowns and all-porcelain crowns are available. The period from the fourth month of fetal life to approximately seven years after birth is the most susceptible period for milk and permanent teeth, so tetracycline drugs must be banned for pregnant women and children.