Pain again after one year of root canal treatment may be due to residual pulpitis, acute inflammation in the apical region, and cellulitis, which is treated with a second root canal, will incision and drainage depending on the situation. In the case of residual pulpitis due to previous imperfect treatment, the tooth usually needs to be drilled to remove the root filling and thoroughly clean out the infected pulp, and if persistent pain occurs, a new root canal may be necessary. In case of acute inflammation in the apical region, the tooth can be drilled open at an early stage, and the inflammatory exudate around the root apex can be drained through the root canal into the oral cavity by means of drainage, which can be combined with the oral administration of anti-inflammatory drugs of cephalosporins, such as cefazolin sodium, and the pain will be relieved significantly. In case of cellulitis and abscess formation, incision and drainage should be carried out as soon as possible to establish a smooth drainage to drain out the pus from the abscess, which can control the inflammation well. If the pain starts again after one year of root canal treatment, it is recommended to consult a doctor in time to find out the cause of the disease, and treat or use medication under the guidance of a professional doctor.