The tooth still hurts after root canal treatment, which may be caused by the body’s foreign body reaction to the treatment material, incomplete control of microbial infection, or the tooth has a periapical cyst. 1. Foreign body reaction. After root canal treatment, due to the operation process will use instruments to prepare the root canal as well as drug rinsing, in the process of operation, the drug may be flushed out of the root tip, periapical tissues can produce reactive pain, the emergence of mild pain can be temporarily observed, if the pain intensifies the need to go to the hospital for treatment. 2. Microbial infection is not completely controlled. After root canal treatment, if the microbial infection inside and outside the root canal cannot be controlled by root canal treatment, acute periapical infection may also occur. 3. Periapical cyst. When a tooth is stimulated by inflammation for a long period of time, a cyst will be formed at the root end. For periapical cysts, apical surgical treatment is often needed, which cannot be cured by root canal treatment. If the tooth still hurts after root canal treatment, you can observe it for a while, and if the pain increases, it is recommended to go to the hospital in time to deal with it.