Inflammation of a tooth that has undergone root canal treatment is usually due to residual pulpitis or periapical inflammation, and the preferred treatment is root canal retreatment. If the preservation value of the affected tooth is not high or the preoperative evaluation of root canal retreatment cannot be satisfied, the affected tooth can be extracted, as follows. 1. Root canal retreatment: It can preserve the function of the affected tooth in the oral cavity, and the treatment process is the same as root canal treatment. After thorough root canal preparation, root canal disinfection and tight filling of the root canal, the residual pulp inflammation and apical periodontitis can be eliminated. 2. Extraction of the affected tooth: If the value of the affected tooth for restoring occlusal function after root canal retreatment is not high, or if the status of the affected tooth is not good, such as tooth looseness of degree III, periodontal pockets and periapical lesion traffic, etc., the affected tooth can be extracted and subsequent restorative treatment can be carried out. There may be other reasons why a tooth that has undergone root canal treatment becomes inflamed, so it is recommended to visit the hospital in time.