Abstract: Objective This study aimed to compare the accuracy of the X-ray digital imaging system Digora and the electronic apex locator Propex on the measurement of the working length of root canal. Methods The study comprised 260 teeth(369 roots)that needed to be extracted from 90 patients. Each tooth was radiographed with the Digora system, and the root length was measured in the Digora digital imaging software with the length tool. The teeth were anesthetized and accessed. The working length of the root canal was determined by the apex locator Propex. Finally, the tooth was extracted, and the real length of the root canal was measured directly. The results obtained with Digora and Propex were compared with the real length. Results The difference between the Digora measured length and real length was (2.163±1.194) mm, where as that between the Propex measured length and real length was (0.214±0.542) mm. When a difference of less than 1 mm was acceptable, the measurement accuracy of Digora and Propex was 21.68% and 91.87%, respectively. When a difference of less than 1.5 mm was acceptable, the accuracy of Digora and Propex was 30.35% and 95.66%, respectively. The measurement accuracy of Digora was significantly lower than that of Propex(P<0.01). Conclusion Digora could easily directly evaluate the root canal length, but it could not directly guide clinical operations. Propex could accurately measure the working length of the root canal.

Key words: root canal therapy, root canal working length, Digora； Propex