If the tooth turns black and also appears painful, consider the possibility of dental caries or pulpitis, as follows: a. Dental caries: dental caries is also called tooth decay, which is a disease that causes progressive and destructive progress of dental hard tissue under the action of multiple factors such as bacterial infection. Patients may show sensitivity to cold, hot, sour, sweet, food inlay and other stimuli, but the symptoms will disappear immediately after the stimuli are removed. Pulpitis: Pulpitis is an inflammatory lesion of the tooth pulp, if the caries is not treated in time, further development can be developed into pulpitis. Acute pulpitis is mainly manifested as spontaneous and paroxysmal pain, pain at night, increased pain when stimulated by temperature, pain cannot be localized, etc. Therefore, if the tooth is black and painful, it is recommended to actively seek medical treatment to avoid aggravating the condition and affecting the prognosis.