The blackness around the teeth may be caused by tetracycline, dental fluorosis, caries and so on. 1. Tetracycline teeth: mostly due to taking tetracycline drugs caused by tooth coloring. The main manifestation of tooth staining, the beginning of the general yellow, with the progress of the disease can appear brown or dark gray. 2. Dental fluorosis: It is caused by inhaling excessive fluorine during the stage of tooth development. The main manifestation is the coloring of tooth enamel, which can appear brown lesions and dark brown changes. 3. Caries: also known as tooth decay, can be caused by bacteria, diet and other factors. Patients can appear yellow-brown plaque, and when not treated in time, cavities can appear. Darkness around the teeth should go to the hospital in time to identify the cause of the disease and take symptomatic treatment to avoid delaying the condition. Daily attention should be paid to regular cleaning of teeth to maintain oral hygiene and cleanliness.