Apical periodontitis in young permanent teeth can prevent the root from developing and forming a trumpet-like structure, which affects the effectiveness of root canal treatment. The apical region of young permanent teeth is in the period of development, and the apical region will change from a flared mouth to a closed state. If apical periodontitis occurs, the development of the apical region will be stopped, which will affect the subsequent filling of the root canal in root canal treatment. Clinically, after the preparation of young permanent teeth with apical periodontitis, calcium hydroxide will be put into the apical area to induce the periapical tissues to make the apical foramen close, and if it can not be closed, the apical opening will need to be closed with a capping agent such as MTA. It is recommended that young permanent teeth with periapical periodontitis should go to the hospital for root canal treatment in time to avoid aggravation of symptoms affecting the formation of the root apex.