Darkening of the edges of the teeth may be caused by pigmentation, subgingival calculus, dental caries and other reasons. 1. Pigmentation: If you smoke for a long time, drink strong tea, coffee or eat heavily pigmented food, it will lead to pigmentation and destroy the enamel on the surface of the teeth, which may cause the edge of the teeth to be discolored and black. 2. Subgingival calculus: due to the lack of attention to oral hygiene, resulting in excessive accumulation of food debris, calcium and phosphorus deposits under the action of bacteria to form subgingival calculus, so there are symptoms of blackened edges of teeth. 3. Dental caries: due to bacteria and food adhering to the edge of the teeth, plaque acid production leads to tooth demineralization caused by caries, eating darker pigmented food may be deposited in the caries cavity, ultimately resulting in the edge of the teeth black. If you have blackened edges of teeth, you should go to the hospital in time for professional diagnosis and treatment. It is recommended to pay attention to oral hygiene, eat more food with coarse fiber, and eat less sweets.