Operating microscope improves negotiation of second mesiobuccal canals in maxillary molars.

This in vitro study investigated the prevalence, location, and pathway of the second mesiobuccal canal (MB-2) in 45 first and second maxillary molars using the operating microscope (OM). Initially location and negotiation of MB-2 were attempted without magnification. Teeth in which MB-2 was not located or could not be negotiated were further explored under OM. Roots where MB-2 could not be negotiated even with OM were cross-sectioned and inspected microscopically. Morphometric measurements were performed to map the location of MB-2. Without magnification an apparent MB-2 orifice was located in 42 teeth and the canal negotiated in 31 (69%). With OM one additional apparent MB-2 orifice was located, and five previously identified canals were negotiated (total 80%). The root cross-sections confirmed the absence of MB-2 in all nine teeth where it was not negotiated. Location of MB-2 varied randomly. In conclusion MB-2 can be negotiated in 80% of maxillary molars, although an orifice is apparent in 96% of the teeth. Ability to negotiate MB-2 is facilitated by OM.