Objective To analyze the causation of treatment failure after root canal therapy. Methods Use root canal retreatment, apical surgery and periodontal surgery to retreat the failed cases. Results In 28 treatment failure of poster teeth after root canal therapy, 11 teeth are intracanal infection, 7 teeth are crown leakage, 7 teeth are root vertical fracture and the other 3 teeth are periodontal infection. Conclusion Intracanal infection is the material cause of failure of root canal therapy, and vertical root fracture is another important cause.
