1. Periodontal disease: teeth with advanced periodontal disease that cannot be treated due to the condition. 2.Dental defect: teeth with serious caries and cannot be restored. However, if the root and periapical condition is good, it can be treated to make pile crown or cover denture without extraction. 3.Periapical disease: The teeth with periapical disease that cannot be preserved by root canal treatment and other methods Medical Education|Education.com collects and organizes. 4, dental trauma: traumatic tooth fracture to subgingival, or at the same time have root fracture, can not be preserved by other treatment methods. The teeth on the fracture line should be decided on a case-by-case basis, and should generally be preserved as much as possible. 5, misaligned teeth: displaced or misaligned teeth should be extracted if they affect function and aesthetics, cause disease or trauma, etc. 6.Obstructed teeth: Obstructed teeth that cause caries of adjacent teeth or repeatedly cause pericoronitis. 7.Extra teeth: Multiple teeth that are misplaced or obstruct the beauty and function should also be extracted. 8.Treatment needs: teeth that need to be reduced due to orthodontics; teeth that should be extracted due to the need of denture repair; teeth that need to be extracted to prevent serious complications before radiotherapy; teeth affected by benign tumors or cysts that should be extracted because they cannot be retained or due to treatment needs. 9. Retained milk teeth: those that affect the eruption of permanent teeth should be extracted. However, if there is no permanent tooth below the baby tooth in the adult dentition or if the permanent tooth is blocked, it is not necessary to extract the baby tooth if it is not loose and has function. 10. Focal teeth: Focal teeth suspected to cause certain diseases should also be extracted. Focal teeth that cause certain local diseases such as osteomyelitis of the jaws and maxillary sinusitis should be extracted after the acute inflammation is controlled.