The possible reasons for black teeth are pigmentation, caries, pulp necrosis, etc., as follows. 1. Pigmentation: Smoking, chewing betel nut, drinking tea and other colored beverages may cause pigment deposition on the tooth surface or tartar, resulting in black teeth. 2. Caries: demineralization and decomposition of dental tissues occur under the action of bacteria and other factors, and the carious tissues can be black after staining. 3. Pulp necrosis: pulp necrosis occurs due to inflammation or trauma, etc. Hemoglobin can form iron sulfide under the action of bacteria into the dentin tubules, resulting in black teeth. There may be other reasons why your teeth are black, so it is recommended that you go to the hospital in time to receive regular treatment as soon as possible.