Two months after the root canal treatment is a little uncomfortable in the heat, may have missed the root canal, residual pulpitis, neighboring teeth caries or hidden cracks, etc., it is recommended to go to the hospital for specific film examination and treatment. 1. The root canal system of the tooth is complex, and there may be the possibility of missing the root canal during the treatment. When the root canal is missed, hot and cold stimulation will cause sensitivity and discomfort or even persistent pain. 2. If the root canal is not enlarged to a certain diameter during the root canal treatment, there may be residual pulp, which may cause pain when exposed to heat. 3. Adjacent teeth with caries may be painful with heat stimulation, and the position of the tooth may not be confirmed during the pain. 4. When there is a hidden crack in the neighboring teeth, there may be pain from heat stimulation and pain from chewing.