Teeth are one of the important organs of the human body. With the development of dentistry, tooth extraction is no longer the main method of treating dental diseases, and doctors will generally do their best to preserve the affected teeth for patients. However, some of the affected teeth must be extracted, that is, the doctor often said that there is no preservation value of the teeth, so as to avoid the deterioration of the condition of the affected teeth to affect the prosthetic restoration as well as the function of the normal neighboring teeth. So, which teeth have been included in the “black list” of extraction? Generally encounter the following nine cases, the doctor will recommend the choice of extraction, that is more conducive to oral health. 1, milk teeth overdue to fall off, affecting the normal eruption of permanent teeth or milk teeth root tip exposure leading to ulcerative gingivitis. 2, the crown caries is more serious, has been unable to restore its shape and function through treatment and repair, or the root of the tooth has lesions, is not suitable for dental crown or overdenture. 3.Severe periapical lesions that cannot be cured by root canal treatment or apicoectomy. 4.Severe periodontal disease, resulting in frequent overflow of pus from the gum pockets, destruction and resorption of alveolar bone, loosening of the teeth by more than 3 degrees, loss of masticatory function, and treatment is ineffective. 5.Wisdom teeth without opposing teeth, misaligned teeth and supernumerary teeth, no chewing function, and often cause tooth plugging, bite wound mucosa or affect the denture repair; or individual teeth are normal, but affect the denture repair and orthodontic needs must be extracted teeth. 6, the position is abnormal, can not be normal eruption and repeated inflammation of blocked teeth; induced by neighboring teeth caries and impede its filling treatment or cause root resorption of neighboring teeth tilted blocked teeth need to be extracted as soon as possible; caused by maxillary sinusitis, maxillary osteomyelitis or recurrent secondary infections of maxillofacial gap of the source of the teeth also need to be extracted in a timely manner. 7, due to trauma caused by tooth splitting or fracture to the neck below the tooth, can not be treated and repaired; or located in the fracture line of the teeth, affecting the healing of the fracture need to be extracted. 8. Teeth that cannot be retained due to necrosis, cyst or benign swelling in the jawbone; or teeth that are located in the radiation area before radiation therapy for malignant tumors need to be extracted in order to prevent osteomyelitis of the jawbone caused by radiation therapy. 9, can induce systemic diseases, such as rheumatoid arthritis, rheumatic heart disease, endocarditis, nephritis and other diseases of the focal tooth. Common focal teeth include pericoronitis, inflammatory periodontal disease, alveolar abscess, etc., which should be considered for extraction if they have not healed after treatment.