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 to promote the healing of periapical lesions by removing necrotic material from 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. First, any cause (including caries, hidden fracture, crown fracture, deformed central tip, excessive wear, retrograde infection of periodontal disease, accidental pulp penetration) caused by pulpitis and pulp necrosis cannot preserve the living pulp. Secondly, apical lesions caused by any cause (including continued development of pulpitis, failure of cadaver plasticization treatment, retrograde infection of periodontitis). Third, physical and chemical causes of pulpal apical infections, such as: pulpal irritation caused by poor temperature of the cushion after filling, current stimulation of different metals, apical infection caused by drugs during endodontic treatment. Fourth, 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 treatment 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. The main advantages of root canal treatment: 1, root canal treatment can maintain the integrity of the natural tooth arrangement, prevent the displacement of adjacent teeth, tooth decay, periodontal disease, can prevent excessive loss of supporting bone after tooth extraction, affecting the appearance of the face and the stability of dentures, but also due to the maintenance of teeth can solve a number of difficulties in the production of dentures. 2.To avoid the incorrect bite caused by early extraction of teeth, thus eliminating the trouble of orthodontic treatment. 3.For patients with serious systemic diseases (e.g. congenital heart disease, diabetes, tuberculosis, hemophilia, pernicious anemia, rheumatic fever, leukemia, hypertension, syphilis, etc.), the use of root canal treatment can reduce the risk. 4.Saving cost. As root canal treatment can keep the natural teeth intact and biologically appropriate state without extracting the affected teeth, it is not necessary to borrow the neighboring teeth to support the denture device, eliminating the abnormal pressure and reducing the cost of denture fabrication. Indications for root canal treatment: 1, including caries, hidden fracture, crown fracture, deformed central cusp, excessive wear, retrograde infection of periodontal disease, pulpitis caused by accidental pulp penetration and pulp necrosis that cannot preserve the living pulp. 2, physical and chemical causes of pulp apical infection, such as pulp irritation caused by poor bedding temperature after filling, current stimulation of different metals, apical inflammation caused by drugs during endodontic treatment, etc. 3, including apical lesions caused by continued development of pulpitis, failure of dry cadaver plastination treatment, and retrograde infection of periodontitis. 4, Degenerative changes of the pulp caused by unknown reasons, such as intracanal resorption and pathological changes of the pulp caused by pulp stone.