I. What is root canal treatment? Root canal therapy, commonly known as “nerve killing”, is the most common and effective international treatment for endodontic disease (commonly manifested as toothache) and periapical disease (commonly manifested as swollen gum pockets). The principle of root canal treatment is to mechanically and chemically remove the infected material from the root canal of a tooth, and to prevent the occurrence of periapical lesions or to promote the healing of periapical lesions that have already occurred by filling the root canal and sealing the crown. Second, the number of root canal treatment visits Root canal treatment is a complex, complete and thorough treatment process. Depending on the condition of the affected tooth, the difficulty of treatment and other factors, root canal treatment usually requires 1-3 times to complete, the specific number of visits should be determined by the doctor after specific examination. If a follow-up visit is needed, it usually takes about 1 week between each visit. Root canal treatment should be followed up on time, so as to avoid the root canal infection caused by the failure or dislodgement of the drug after the sealing time is too long, which not only increases the number of treatments and prolongs the course of treatment, but also may bring difficulties to the treatment and even lead to root canal treatment failure. Third, post-operative considerations of root canal treatment Because of the difficulty of root canal treatment operation and the difference of individual patients’ physical acceptance, post-operative reactions may sometimes occur in different degrees during root canal treatment, such as slight pain or swelling discomfort of the tooth. Usually, post-operative reactions after root canal treatment are temporary and can generally return to normal on their own. If the pain or swelling is severe, further consultation with your doctor is required. Avoid biting on the affected tooth during root canal treatment. Since the affected tooth has a large crown defect, it cannot withstand large occlusal forces and may lead to tooth extraction if it splits. Therefore, it is necessary to avoid biting on the affected tooth during the root canal treatment. After the root canal treatment, due to the small amount of remaining tooth, it is recommended to have the tooth crowned to repair the missing tooth tissue if possible, so that the tooth will not be split and extracted due to excessive biting force. The success rate of root canal treatment According to the literature, the success rate is about 90% after perfect root canal treatment for the first time, which is a very high success rate in the treatment of diseases. The success rate of re-treatment of teeth with a poor prognosis after previous endodontic treatment decreases, and the more difficult the root canal retreatment is, the lower the success rate. The success rate of a group survey is not really meaningful for an individual patient; for an individual patient, a successful treatment is 100% success and a failure is 100% failure. The possibility of failure in any treatment is often determined by the limitations of medical science’s understanding of the disease, and informing patients of the prognosis and complications of treatment is respectful of their right to know.