Methods: Thirty-six teeth of mature lower first molars with root curvature in the mesiodistal plane ranging from 20° to30° were used . The canal length of all teeth was standardized to 16 mm from apical foramen by cutting the occlusal surfaces. The teeth were divided into two experimental groups of 16 each. The four remaining teeth served as uninstrumented control and were used to evaluate the cone beam computed tomography imaging system. In group A, the mesiobuccal canals were prepared with Mtwo Ni-Ti rotary files #20/06, 25/06, 30/06, 35/06 and 40/06 respectively using continuous rotation. In group B, the mesiobuccal canals were prepared with one Reciproc rotary file # 40/06 with reciprocating movement. All teeth were cross-sectional scanned by cone beam computed tomography before and after instrumentation at the level 1.5, 3, 4.5, 6 and 7.5 mm from apex. These images were used to analyze canals transportation. Data were analyzed using independent t test and Tukey test.
Results: There was no significant difference between the two experimental groups in canal transportation at any level (P>0.05). At 1.5 mm from the apex the canal transported outside the curved root but at level 6 and 7.5 mm the canal transported inside the curved root
Conclusions: Root canals with mesiodistal curvature ranging from 20° to 30° were prepared with Mtwo or Reciproc NiTi files to the size 40/06. There was no significant difference in canal transportation.