Root canal therapy is a treatment procedure for tooth, pulp, and apical lesions. Root canal therapy is a treatment method to prevent the occurrence of periapical lesions or promote the healing of periapical lesions by removing the necrotic material in the root canal, performing proper disinfection, and filling the root canal to remove the adverse stimulation of the root canal contents to the periapical tissues. Indications for root canal treatment 1. Pulpitis and pulp necrosis caused by any reason (including caries, hidden fracture, crown fracture, deformed central tip, excessive wear, retrograde infection of periodontal disease, accidental pulp penetration) cannot be retained in the case of live pulp. Wu Shichao, Department of Prosthodontics, Tianjin Tanggu District Stomatological Hospital 2, apical lesions caused by any cause (including the continued development of pulpitis, failure of dry cadaver plasticization treatment, retrograde infection of periodontitis). 3, physical and chemical causes of pulpal apical infection, such as: pulpal irritation caused by poor temperature of the cushion after filling, current stimulation of different metals, apical inflammation caused by drugs during endodontic treatment. 4. Degenerative changes of the pulp caused by unknown reasons, such as root canal resorption, pulp stone caused by pathological changes of the pulp. The process of root canal therapy is to prevent the occurrence of periapical lesions or promote the healing of periapical disease by thoroughly removing the infected pulp as well as the infected dentin and toxic decomposition products through root canal irrigation, disinfection and tight filling of the root canal to isolate the bacteria from entering the root canal and reinfecting it. The success rate of root canal treatment is clinically reported to be over 90%, which is currently the best treatment method to preserve the affected tooth. In general, root canal therapy is indicated for pulpitis, pulp necrosis, and all types of periapical infections. In particular, root canal therapy is the only treatment option for teeth with residual crowns that require pile crown restoration in the prosthodontics department.