The operating microscope enhances detection and negotiation of accessory mesial canals in mandibular molars.

Introduction: Detection and negotiation of accessory mesial canals in mandibular molars was investigated with the aid of magnifying loupes or the operating microscope.

Methods: First and second mandibular molars (n = 96) were mounted in mannequins. Three independent investigators (endodontists) prepared access cavities using 4.5x loupes, attempting to detect and negotiate accessory mesial canals with ultrasonic instruments. If detection or negotiation was unsuccessful, the procedure was continued using the microscope. The location of accessory mesial canals was mapped in relation to the main mesial canals, and their pathway shown with inserted files. The mesial roots were cross-sectioned at three levels to inspect for nonnegotiated accessory mesial canals.

Results: With the microscope, the number of detected accessory mesial canals increased from 8 (16%) to 9 (18%) in first molars and from 8 (16%) to 11 (22%) in second molars. Negotiated accessory mesial canals increased from 6 (12%) to 7 (14%) and from 5 (10%) to 9 (18%) in the first and second molars, respectively. All 20 detected accessory mesial canals were located in the mesial subpulpal groove, closer to the mesiolingual canal (45%), in the middle (30%), or closer to the mesiobuccal canal (25%). All negotiated accessory mesial canals merged with one of the main two canals. Cross-sections of the roots confirmed that no accessory canals were present in addition to those negotiated.

Conclusions: Within the limitations of this study, more accessory canals were detected and negotiated when using the microscope compared with loupes. This improvement was more pronounced in second molars than in first molars. All negotiated accessory canals merged with either one of the main mesial canals.