Abstract: [Abstract] Objective：To compare the differences between periapical radiography (PR) and cone-beam computed tomography (CBCT) in diagnosing root canal treatment (RCT) failure cases. Methods：The radiography data of RCT failure cases were retrospectively analyzed. The differences between PR and CBCT in analyzing the pathogenesis and state of RCT failure cases were compared. Results：A total of 210 RCT failure cases’ PR and CBCT images were collected and analyzed. Under-filling teeth and missed root canals mainly account for the failure in RCT. CBCT could judge the quality of root canal filling and the type of root fracture more accurately. The detection rate of missed root canals of CBCT was 14.8% higher than that of PR, and the detection rate of root fracture of CBCT was 5.7% higher than that of PR. Conclusion：CBCT images were better than PR in analyzing the pathogenesis and state of RCT failure cases, which will offer more significances in root canal retreatment.

Key words: Key words: periapical radiograph, CBCT, root canal treatment