Cavum trepanation of tooth 46 was cautiously done with high-speed diamond bur and with low speed round burs because the amalgam filling made it impossible to measure the position of the pulp chamber. In addition, it was likely that the pulp chamber was largely or totally obliterated. The distance from the occlusal surface to the furcation was measured from the radiographs to minimize the possibility of perforation. Fiber optics was used to study the bur cavity and to locate the canal openings. Distal canal was located first, because radiographs indicated that it would be easier to find, and after that locating the mesial canal openings would be easier. The mesial canals were found and penetrated after sequential use of a sharp probe and size 010 round bur under continuous use of fiber optics. Nr. 06 K-file was used to study the mesial canals.

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