Black lines on teeth are mainly caused by pigmentation or caries, and it is recommended to seek medical treatment for pigment removal or restorative filling treatment for caries. 1. Hyperpigmentation: Long-term consumption of dark-colored food (such as coffee, strong tea, soy sauce, etc.), smoking or taking certain dark-colored medications (such as iron) will lead to pigment deposition on the tooth surface and the fossa and other locations; and then appear in the teeth of the black line of the symptom, the need to seek medical treatment to remove the pigmentation treatment (such as sandblasting, ultrasonic scaling or polishing, etc.). 2. Dental caries: the position of the tooth fossa and fissure is easily due to food deposition or cleaning is not in place, there will be a linear black caries; must seek medical treatment for caries filling and repair, that is, the black caries part of the abrasion with oral restorative materials for the repair of the defective parts. It is recommended to consult a doctor for a clear diagnosis of the black line on the teeth to avoid delaying the condition.