The most common cause of tooth defect is caries, followed by trauma, abrasion, cuneiform defect, acid erosion, developmental malformation, as follows: 1. Caries is caused by bacterial action to demineralize the hard tissue and organic decomposition, which is manifested as hard tissue discoloration, decalcification, softening, cavity formation, and further can develop into pulpitis, periapical inflammation, periapical abscess, and serious caries can form residual crown or residual root; 2. Trauma refers to the fracture of the tooth caused by the accidental impact of the crown or biting hard objects, and the chance of trauma to the front teeth is relatively high. Because of the decrease of its own tooth strength, even the normal biting force dead pulp teeth or hidden cracked teeth are easy to break; 3, wear and tear is manifested as the crown biting surface is reduced, which will affect the chewing function and the beauty will also be affected; 4, wedge-shaped defect that the people often say that the tooth neck feels very sour or hot and cold uncomfortable when brushing teeth is caused by wedge-shaped defect; 5, developmental malformation such as fluorosis, tetracycline teeth, too small teeth, conical teeth, etc.; 6 , acid erosion caused by dental defects.