The occurrence and development of wedge defects are related to the following factors: 1. Inappropriate brushing method The transverse brushing method on the labial (buccal) side of the teeth was the first factor proposed to cause the occurrence of wedge defects. It is based on the fact that this disease is not seen in animals, does not occur in young people, and wedge defects rarely occur in those who do not brush their teeth. The isolated experiment of cross-brushing the cervical part of the tooth can create a wedge defect and is more than twice the amount of wear of the dental tissue caused by the rotary method of brushing. 2, the role of acid The acidic environment in the gingival sulcus can demineralize the cervical tissue and make it easy to be defective after abrasion. The acidic secretion of salivary glands, the preference for acid food, changes in saliva pH, acid reflux from gastric disease, etc. are all related to the occurrence of defects. Isolated teeth experiments with acid and cross-brushing can form a wedge-shaped defect in the cervical part of the tooth. 3, the characteristics of the structure of the cervical part of the tooth The junction of the enamel and bone of the cervical part of the tooth is the part of the entire tooth with the least amount of enamel and bone coverage or no coverage, which is the weak link of the tooth structure; the gingiva is prone to inflammation and atrophy at this place to expose the root surface, so this part has the lowest wear resistance. 4, stress fatigue In the process of chewing movement, the size and direction of the occlusal force accepted by the tooth changes periodically with time, and the hard tissue of the corresponding part of the tooth receives alternating compressive and tensile stresses of different sizes. Although the value of each alternating stress is not large, but the long time repeatedly occurring in the stress concentration of the site can appear small damage, that is, stress fatigue. The cervical part of the tooth is the intersection of three hard tissues of the tooth, and the mechanics of materials suggest that the intersection of substances of different structures is the site of stress concentration when the tooth receives occlusal forces. Over time, minor stress-fatigue damage accumulates in the hard tissues of the cervical region and fatigue microfractures occur, the term used by Levitch (1994) to describe this lesion, “internal fracture” (abfraction). This internal change significantly reduces the resistance of the hard tissue of the cervical region to mechanical wear and chemical decay. Stress fatigue in the cervical region is therefore considered to be an intrinsic factor in the pathogenesis of wedge defects. The cumulative effect of stress fatigue injury explains the clinical phenomenon that wedge defects tend to occur in middle-aged and elderly people, in tooth positions subjected to high occlusal forces and in areas of tooth stress concentration. The occurrence of wedge defects in the cervical part of lingual teeth has been reported both domestically and externally in recent years, which can also serve as a corroboration of this mechanism. Clinical manifestations It is usually seen in bicuspids, followed by first permanent molars and cuspids in patients of middle age or older, sometimes involving all teeth before the second permanent molar. It is common to see several adjacent teeth with different degrees of defect, and the more severely defective teeth often have 10-20 functional mobility and lateral occlusal working side interference. In young patients, wedge-shaped defects of single teeth are rare, and all affected teeth have occlusal interference.