To investigate the efficiency of combined application of dental endoscope and ultrasonic technique in treating concealed root canals.

87 complicated and difficult cases which were not found root canals during endodontic treatment by naked eyes were selected. The canal orifices were probed and negotiated with the aid of dental endoscope and ultrasonic instruments. And the success rate was recorded.

121 concealed root canals which from 87 complicated and difficult cases were classified into 64 calcified canals, 39 narrow curved canals and 18 canals with anatomic variation. Among them, 94 canals were found and then negotiated, and the total success rate was 77.68%. There was no significant difference between the success rates in treating calcified root canals, narrow curved canals and canals with anatomic variation (χ²＝5.477, P > 0.05).

The combined application of dental endoscope and ultrasonic instruments can effectively improve the success rate of finding and negotiating concealed canals.