Darkening of teeth is usually caused by pigmentation, dental caries and pulp necrosis. 1. Pigmentation: Long-term smoking, betel nut chewing or habitual drinking of strong tea, coffee, cola and other dark-colored diets can lead to pigmentation on the surface of the teeth, so that the teeth become yellow, black. 2. Dental caries: Due to bacteria and food adhering to the tooth surface, plaque acid production leads to tooth demineralization causing caries, showing chalky white color, and because of the pigmentation in the demineralized parts of the teeth, it leads to darkening of the teeth. 3. Pulp necrosis: due to pulp necrosis, resulting in the formation of more bacteria in the root canal of the tooth, and the tooth loses the blood vessels and nerves and lymphatic organizations that nourish the tooth, the tooth does not have sufficient nutrition will slowly darken and blacken. If you have black teeth, you should go to the hospital in time to have the cause clarified and treated by the doctor.