The purpose of this study was to evaluate the root configurations and the canal characteristics of two human extracted mandibular second molars respectively possessing an extra root by using a microfocus X-ray CT apparatus. The results were as follows: 1) The two teeth from persons of unknown age and sex were mandibular left second molars with the appearance of 5 cusps. It was not possible to clarify their occlusal fissure patterns such as Dryopithecus pattern due to apparent occlusal wear. 2) Although the teeth had two roots, the mesial and the distal, there was an extra root on one of them on the buccal side of the cervical-mid root stump. The distance from the cervical junction to the level of funcation was two to three millimeters. The extra root with a tiny single canal extended parallel to the long axis of the mesial root. The tooth showed 3 canals with 3 apical foramina. The extra root of the other tooth branched out on the lingual side of the near level of bifurcation between the mesial and distal roots. The tooth showed 4 canals with 3 apical foramina. The mesial root divided into 2 canals, but merged into 1 apical foramen. The extra root and canal were very slender. 3) The microfocus X-ray system was useful to examine rare puzzling supernumerary roots and their microscopic canals in mandibular molars. Dental practitioners should be aware of possible root canal variations in all teeth so that they can be treated successfully.
