A tooth that has undergone root canal treatment hurts again after one year, it may be due to inflammatory reaction in the mouth, such as periodontitis or gingivitis; or the tooth has fractured after root canal treatment. 1. Periodontitis: If you don’t pay attention to hygiene after root canal treatment, periodontitis may be induced, resulting in redness, swelling and pain of periodontal tissues, causing toothache. Treatment should be systematic periodontal treatment such as cleaning, scraping, etc., the serious condition can be systemic medication, such as oral metronidazole, tinidazole, etc., periodontal pockets of tissue can be injected with minocycline gel. 2. Gingivitis: If the teeth are not cleaned frequently after root canal treatment, the formation of plaque may stimulate the gum tissue, gingivitis is easily triggered. Treatment needs to clean up the embedded food as soon as possible, and then rinse with hydrogen peroxide, if necessary, can be used to iodine preparation for gingival sulcus medication. 3. Tooth fracture: after root canal treatment, the tooth is not well protected, easy to fracture, thus causing toothache. It is necessary to use braces for fixation as soon as possible, if there is no value in retaining the intention, the tooth can be extracted in time. If the toothache occurs, it is recommended to observe for a period of time, and if it does not go away for a long period of time, we should consult a doctor in time and seek the doctor’s advice, and then choose the regular treatment, and the use of medication should be in accordance with the doctor’s instructions.