Methods: In this in-vitro randomized controlled study twenty sixth mesial root canals of mandibular molar with curvature between and length of 10mm were divided into two groups of 13. The canals were prepared in group A with RaCe and in group B with ProTaper files following the manufacture's instructions. Photographs of each root were captured in 2,4,10 mm cross section before and after canal shaping and superimposed with Adobe photoshop software. Canal transportation and changes in canal centering were analyzed. Statistical analysis was performed using SPSS 11.5 software for comparison of each cross- section.
Results: Two NiTi rotary systems had prepared canals without transportation and deviation in original shape of canals, and remained centered within the canal with minimal deviation from the canal path. Two NiTi rotary systems are independed to transportation and canal centering in all of cross sections. There were no significant differences between the two rotary systems.
Conclusions: The two NiTi rotary systems respected original root canal curvature without transportation and deviation in shaping of canal. Both of systems can be recommended for clinical use.