Toothache one year after root canal treatment may be the failure of that root canal treated tooth or longitudinal fracture of the root, or it may be the pain of other teeth in the mouth. 1. Root canal treated tooth: If the body’s resistance is low, bacteria located inside or outside the root canal after root canal treatment may cause root canal failure if they multiply and the body is unable to resist the virulence of the bacteria. At this point, re-root canal treatment is considered depending on the situation. It may also be due to the tooth after root canal treatment without braces, biting and eating hard objects caused by the tooth hidden crack. 2. Pain in other teeth: If acute pulpitis occurs in other teeth in the mouth, it is usually impossible to locate the painful tooth, and dental caries can be seen in the oral examination. Root canal treatment one year after the toothache is recommended to the hospital in time to deal with.