In young permanent teeth with severe pulpal or periapical lesions occurring before the root development is complete, the treatment is based on the control of infection and the preservation of the pulp in the apical region or the deposition of hard periapical tissues with drugs and surgical methods to promote the continued root development and apical formation. The preferred clinical drug is calcium hydroxide preparation. Indications Young permanent teeth in which the pulp has reached the root pulp and the pulp cannot be preserved or cannot be fully preserved. Young permanent teeth with total pulp necrosis or complications of periapical disease. 2. Treatment stages The first stage is to eliminate the infection and periapical lesions and to induce root development. The second stage is to close the root canal after root apical hole closure. The general interval is about 6 months to 2 years. 3. Treatment steps (1) Routine preparation of the cavity to open the pulp and extract the pulp, avoiding damage to the tooth papilla. In case of live pulp, it can be done under local anesthesia. (2) Root canal preparation: remove the infected necrotic pulp tissue in the root canal, and rinse the root canal thoroughly with 3% hydrogen peroxide solution and physiological saline. In case of acute clinical symptoms, emergency treatment should be done first to open the root canal, drain effectively, and continue treatment after decreasing inflammation. (3) Root canal disinfection: aspirate the root canal, seal the root canal with less irritating drugs, such as camphor phenol, pomegranate oil, iodoform paste, antibiotic paste, etc. (4) Drug induction: after the clinical absence of symptoms and no exudation in the root canal, the root canal is introduced with drugs that can induce apical development and formation, and calcium hydroxide preparations are preferred. (5) Temporary filling of the cavity, follow-up observation; review every 3-6 months, pay attention to the presence of clinical symptoms during the review, routine X-ray film ship to inspect the periapical, apical formation and drug absorption. Change the medication regularly until the root tip is formed or the root end is closed. (6) Conventional root canal filling: When the X-ray shows apical lengthening or calcified tissue deposition and closure of the root end, conventional root canal filling can be performed. (1) Thorough removal of infected material from the root canal is an important factor in eliminating periapical inflammation that leads to apical formation. (2) When removing the pulp in the root canal, the pulp fragments should be removed with a root canal file against the root canal wall according to the working length measured by X-ray, to avoid pushing the infected material out of the root tip or puncturing the apical tissue. (3) Regular review, regular change of medication, when the X-ray tripod shows healing of periapical lesions, the root continues to develop and take shape, or when there is calcified material deposited at the tip of the root when the root canal is probed inside the root canal, routine root canal treatment can be performed. (4) The course and effect of apical induction molding depends not only on the degree of pulpal or periapical lesions, but also on the degree of root development and the health status of the patient. Therefore, the treatment is more difficult and the course of treatment is longer. (5) Teeth with underdeveloped roots, the medical. The cells in the apical part of the root are potentially capable of cell differentiation after the inflammation is eliminated, so it is very important to control the infection and remove it. The living pulp in the apical part should be preserved as much as possible; the papilla should be protected; and the epithelial root sheath function should be restored.