The causes of black teeth, including pigmentation, filling staining, etc., are as follows: First, when often drinking tea or smoking, smoke spots and pigments, etc. can be deposited on the adjacent surface of the teeth, which is not easy to clean to form black. Second, when applying silver amalgam filling on the adjacent surface of the teeth, it may cause staining of the nearby dental tissues and make the tooth gap black. When composite resin is applied to fill the tooth, if it is not polished, it is easy to adsorb the exogenous pigment, which also makes the tooth gap black. Third, when there is a large amount of calculus attached to the cervical part and root surface of the teeth, it will stimulate the gums to swell and bleed, resulting in the blackening of the gap between the teeth. After the adjacent space of teeth is often embedded with food, and the cavity is formed by destroying the adjacent point, the tooth body tissue is damaged, and there is obvious blackening at the gap of teeth from the buccal and lingual side.