Objective To evaluate the effect of using cone-beam computed tomography（CBCT） and dental operating microscope（DOM） in treating maxillary molars containing bifurcative canals buccally. Methods 304 endodontically treated maxillary molars（159 maxillary first molars and 145 maxillary second molars） were included. After preparing access to pulp chamber, the number of canal orifices and location in the pulp chamber floor of each tooth were recorded. For those teeth with bifurcative canals buccally confirmed by preoperative radiographs, the root canals were negotiated by naked eyes firstly, then under DOM according CBCT results. Following working length determination, the root canals were prepared by step-down technique and obturated with cold lateral condensation technique. The efficiency was evaluated with radiographs before, during and after operation. Results In 304 maxillary molars, 51 molars were found to have two canal orifices（buccal one and palatal one） in the pulp floor, 30 bifurcative canals buccally（8 upper first molars and 22 upper second molars） were found. CBCT information indicated the level of bifurcation in buccal canals were 3-8 mm under the pulp chamber floors. In 30 maxillary molars, 7 teeth treated by X-rays and eyes could be negotiated, 22 teeth treated by CBCT and DOM could be negotiated and were well instrumented and filled by evaluating with radiographs during and after operation, 8 teeth with deep divergent MB2 canals or calcified canal could not be negotiated. Conclusion Operative field can be located precisely by CBCT and dental operating microscope that could be effective method in treating these sort of canals.
