Abstract: Abstract: Objective To evaluate the combined application of CBCT and microscopic ultrasonic technique in management of complicated root canal therapy of premolars and their clinical efficacy. Methods 20 premolars with aberrant canals which could not be successfully managed by conventional methods were selected. CBCT scan was conducted before the operation and the image results were analyzed. Then the exact number, morphology and calcification of the root canals were obtained. Under the dental operating microscope, ultrasonic instruments were used to locate and probe the root canal. The root canals were shaped using Ni-Ti rotary instrumentation and obturated with warm vertical compaction technique. The types of the variant root canal configuration and complications during treatment were recorded. The curative effect was evaluated. Results 19 teeth among 20 were successfully managed with a rate of 95%. There was no ledge, perforation and instrument separation in all cases. The type of multiple canals in 20 premolars was mainly Type V (Type 1-2), followed by type III (type 1-2-1). Conclusions The use of CBCT and dental operating microscope can greatly facilitate successful endodontic therapy in aberrant root canal system of premolars. CBCT plays an important role in guiding the preoperative detection and intraoperative position of the additional root canals.

Key words: CBCT, dental operating microscope, ultrasonic technique, aberrant root canal