The darkening of the recesses of the back teeth may be related to simple hyperpigmentation, pulp necrosis, caries and other reasons. 1. Simple pigmentation: such as drinking tea, chewing betel nut and other reasons, can make the teeth appear pigmentation, the phenomenon of darkening of the recesses of posterior groove teeth. 2. Pulp necrosis: necrosis of the pulp tissue of the posterior alveolar teeth is decomposed under the action of bacteria, and tooth discoloration and blackening of the depressions can occur. 3. Dental caries: caries in the role of bacteria to destroy dental tissue, the formation of carious tissue, the appearance of the groove of the teeth in the recesses of the black. It is recommended to go to the hospital in time to clarify the cause of the darkening of the recesses of the back teeth, and if treatment is needed, it should be standardized under the guidance of the doctor, so as not to delay the condition and bring adverse effects to the body.