Factors affecting the negotiability of second mesiobuccal canals in maxillary molars.

Factors affecting the negotiability of MB2 canals were evaluated by studying 87 extracted maxillary molars that had undergone previous endodontic treatment in the endodontic technique laboratory. The mesiobuccal roots were resected and radiographed, after which a #08 file was used in an attempt to negotiate those roots with the potential for a second mesiobuccal canal. The file was then intentionally separated in the MB2 canals that could be negotiated. The roots were decalcified, cleared, and observed under a stereomicroscope. Several factors that could interfere with the total or partial negotiation of MB2 canals were identified and included accumulation of debris and sealer that blocked access to these canals, dentinal debris produced with the pathfinding instrument, the presence of anatomical variations, diffuse calcifications, and pulp stones.