The blackening of the root of the tooth, which should refer to the blackening of the cervical region of the tooth, may be caused by caries, calculus, etc. 1. Caries: the etiology of caries is related to bacterial infection, eating too much food with high sugar content, poor hygiene habits and other factors. Patients will appear white, yellow-brown plaque on the surface of the teeth, and with the development of the disease, caries can be formed, manifested as the neck of the teeth black. 2. Dental calculus: dental calculus may be caused by poor hygiene habits, mineral deposition, dental restoration surface roughness and other factors. Patients in the gum margin below the root surface, there will be brown or black stones, can be accompanied by bad breath, gums red and swollen and other symptoms, manifested in the neck of the teeth black. There may be other reasons for the darkening of the neck of the tooth, and the patient needs to go to the hospital to find out the cause of the disease.