In some patients, the darkening of the teeth may be due to calcification deposits in the dentin as we age, which may lead to yellowing or darkening of the teeth. In addition, pigmentation, caries, long-term medication, gum necrosis and many other reasons may cause patients to have blackened teeth. 1.Cause: 1.Pigmentation: if there is long-term smoking or often drink a lot of coffee, cola, strong tea and other beverages, the individual’s teeth will leave cigarette stains, coffee stains and other pigmentation, thus making the teeth black; 2.Caries: due to food or bacteria attached to the surface of the teeth for a long time, thus making the teeth appear to be corroded, demineralized and other carious conditions, resulting in the patient’s teeth darkening; 3.Long-term Medication: If the patient takes tetracycline or fluoride medication for a long time, the medication may be deposited on the surface of the teeth, causing the enamel to be damaged, which leads to the blackening of the patient’s teeth; 4, pulp necrosis: If the patient’s dental nerve is necrotic due to trauma and other reasons, the blackening of the teeth may occur. Second, treatment: 1, scaling: mainly used for teeth darkening caused by pigmentation, can remove the stain residue on teeth to a certain extent; 2, teeth cold light whitening: can remove the melanin attached to teeth by low temperature cold light technology, whitening effect is obvious, but there is a certain damage to tooth enamel; 3, teeth laser whitening: apply bleaching drugs on the tooth surface, and make the drugs penetrate into the teeth quickly through laser heating It can remove plaque, tobacco stains, etc.; 4, Other: If the patient has caries or pulp necrosis, it is recommended to have root canal treatment first, then full crown restoration, and finally tooth bleaching. People with deep dentin staining caused by fluorosis and tetracycline teeth can choose dental veneer restoration. Patients are advised to pay attention to oral hygiene, keep the good habit of brushing or rinsing after meals, try to avoid coffee, cola, strong tea and other drinks that can stain the teeth, and avoid smoking to reduce the occurrence of tooth darkening.