Root canal therapy (RCT) is the most common and effective treatment for endodontic and periapical disease internationally. The principle of root canal therapy is to mechanically and chemically remove most of the infected material from the root canal and to prevent the development of periapical lesions or to promote the healing of existing periapical lesions by filling the root canal and sealing the crown. Indications Root canal therapy is indicated for teeth diagnosed with endodontic or periapical disease that require removal of pulpal tissue and removal of infection from the root canal system with the goal of preserving the entire affected tooth or root, but requires the affected tooth to have adequate periodontal tissue and bone support, and in some cases, some including trauma, restorative dentistry, periodontal surgery, or other treatment needs, also require removal of the pulp and root canal therapy. Introduction Root canal therapy is a more complex endodontic treatment that uses many instruments and steps, requiring multiple treatment steps and multiple x-rays to complete the entire procedure. Complications During and after treatment, pain and other discomfort may occur, most of which are normal. If the pain is severe, accompanied by local swelling and systemic reactions, you should follow up promptly for further treatment as appropriate. In case of complex root canals (bending, narrowing, calcified obstruction, broken instruments, lateral penetration) or other special conditions, root canal treatment will be more difficult and require the use of special equipment and materials, and the treatment time will be increased accordingly. In the case of complex root canal treatment, broken instruments may occur, but it is not required to forcibly remove the broken instruments. After root canal treatment, the body has a repair process and can be reviewed periodically to see how the tissue is healing. For a considerable period of time the patient may feel discomfort in the tooth being treated. If the situation is not progressively worse, an observation approach can be taken, but medical advice should be followed for a timely review. Re-treatment Root canal treatment is unsuccessful in a few cases, and indeed in cases where conventional root canal treatment is not possible or has failed, some cases can be treated by continuing treatment with apical surgery, and some cases are treated by extraction. During and after root canal treatment, the tooth is prone to splitting, which leads to extraction. If the tooth defect is large, please follow the doctor’s instructions to have a crown restoration in time after treatment.