The cavity in the tooth can be caused by caries, trauma, cuneiform defect or abrasion, but for the cavity in the tooth, there are only two possible cases: caries and cuneiform defect. Caries is the most common clinical condition of tooth cavity, which is a disease caused by bacteria invading the hard tissue of the tooth and causing decay, disintegration and damage to the hard tissue of the tooth. In this case, the general treatment is to remove the decayed part with the power system of dentistry, and then fill the cavity with the filling material. In addition to cavity, there is also a kind of wedge-shaped cavity in the cervical part of the tooth, which is caused by improper brushing method and long-term horizontal brushing method, and this kind of defect can be repaired in the same way as caries in the early stage.