The causes of a small defect on the tooth surface include: 1, lack of calcium, phosphorus and other elements during embryonic development or viral infection resulting in enamel hypoplasia and tooth surface defects. 2, with severe fluorosis the enamel surface will appear dark brown plaques or form band depressions, sometimes manifesting as pits and pits. 3, when traumatic injury occurs part of the tooth fracture, producing defects, sometimes accompanied by dentin hypersensitivity. 4, when chewing hard food often, multiple cracks can appear on the tooth surface, sometimes accompanied by dentin hypersensitivity. 5, when chewing steep cusps or marginal ridges can produce stress concentrations. The surface of the tooth will be cracked, and the tooth will be partially missing due to the fatigue of the tooth tissue after a long time. 5. The presence of steep cusps or marginal ridges on the tooth surface can produce stress concentration and cause fracture of the tooth tissue when chewing hard objects, thus producing defects.