1.Stayed milk teeth: The milk teeth are retained, affecting the eruption of permanent teeth, or the inflammation cannot be controlled, repeatedly causing acute attacks, and the roots of milk teeth have been absorbed, obviously loose or the roots of milk teeth are exposed, even piercing the surrounding soft tissues. 2.Serious caries, worm teeth: Such as caries and so on make the teeth seriously destroyed. 3. Apical lesions: teeth that cannot be preserved by root canal treatment, apicoectomy or tooth replantation. The implantation department of Hefei Stomatological Hospital Liu 4, advanced periodontal disease: the affected tooth has more than Ⅲ degree loosening, after treatment is ineffective, really can not be preserved. 5, trauma caused by the root of the tooth loose, can not be repaired. The teeth located on the fracture line cannot be preserved. 6.Displaced or misaligned teeth: Displaced or misaligned teeth, such as those that affect normal occlusion, prevent chewing function or affect aesthetics, or elongate due to the absence of jaw teeth, causing food embedding and biting soft tissues of the opposite jaw – or those that affect denture repair due to partial tooth loss, or those that need to be extracted due to orthodontics. 7.Interrupted teeth: Repeatedly caused by pericoronitis, formed chronic fistula, and some lead to adjacent teeth 8.Focal teeth: such as those caused by collar facial cellulitis, osteomyelitis of jaw bone, maxillary sinusitis should be extracted after the acute inflammation is controlled, and focal teeth suspected of rheumatism, nephritis, eye disease (such as iris ciliary inflammation), optic neuritis, retinitis and other diseases can be extracted to cooperate with their treatment.