Black stains on the inside of the teeth can be caused by pigmentation, calculus, etc. Black stains on the inside of the teeth can be removed by ultrasonic cleaning with tooth polishing. 1. Hyperpigmentation: black stains may be caused by long-term smoking, drinking strong tea on the surface of the teeth caused by hyperpigmentation. It is recommended to pay more attention to oral hygiene habits, brush your teeth on time, and try to avoid smoking, drinking strong tea and other habits. Secondly, it can also be improved by sandblasting and polishing, gingival scaling and so on. 2. Dental calculus: this disease is due to dental plaque attached to the surface of the teeth is not timely cleaned up and formed, will gradually be deposited as black stains on the inner side of the teeth, the patient can cooperate with the doctor to take subgingival scraping or gingival scaling to remove. It is recommended that patients with black stains on the inside of the teeth go to the hospital to clarify the specific cause and cooperate with the doctor for active treatment.