An SEM investigation of the mesiolingual canal in human maxillary first and second molars.

The mesiolingual orifices of 21 maxillary first molars and 37 maxillary second molars were examined with the scanning electron microscope. The mesiobuccal roots of these teeth were also typed by means of a clearing technique. The results demonstrated that 90% of first molars and 70% of second molars had two canals in the mesiobuccal root. Type 3 canal systems occurred in 33% of first molars and 35% of second molars. Eighty-one percent of first molars and 59% of second molars had a separate mesiolingual canal orifice. The mean diameter of the mesiolingual orifice was 0.49 mm in first molars and 0.42 mm in second molars. The mean distance of the mesiolingual orifice from the mesiobuccal orifice was 2.31 mm in first molars and 2.06 mm in second molars. In type 3 roots, the average distance of the mesiolingual foramen to the anatomic apex was 2.0 mm for first molars and 1.45 mm for second molars.