This study investigated several parameters of root canal preparation with three different rotary NiTi systems: Hero Shaper, ProTaper, and RaCe. The parameters evaluated were: changes in root canal volume and cross-sectional area, canal transportation, and working time. Curved, mesial molar roots were scanned in a computed tomography (CT) unit before and after instrumentation. Cross-sectional views of each canal were obtained at 1 mm intervals. Postinstrumentation volume and cross-sectional area of root canals and the extent of transportation were calculated using image analysis software and, thereafter, subjected to statistical analysis. ProTaper removed significantly more dentin than Hero Shaper (p < 0.05). Instrumentation increased the cross-sectional area at all cutplanes, while the difference between test groups was not significant (p > 0.05). RaCe files significantly transported the canals at the coronal level (p < 0.05). There was no difference between any rotary systems in regards to working time.