The correct term for root infection is periapical periodontitis, periapical periodontitis root canal treatment for many recurrences if the affected tooth still has retention value, feasible apical surgery, if the affected tooth retention value is not high, feasible tooth extraction, as follows. 1. Apical surgery: for teeth that have failed root canal retreatment, under the magnification of an operating microscope, the apical root is surgically removed by using ultrasonic instruments and microsurgical instruments, the necrotic and infected tissues in the operated area are removed and the root canal system is tightly closed. 2. Tooth extraction: If the affected tooth is accompanied by serious periodontal lesions, such as too little periodontal supportive tissue, deep periodontal pockets, and severe tooth loosening, the retaining value of the affected tooth is not high, and the tooth can be extracted to make a prosthetic restoration. The same disease, the patient’s condition is different, the choice of treatment is different, it is recommended to go to the hospital for consultation.