Introduction: The purpose of this study was to compare the shaping ability of ProTaper, Mtwo, BioRaCe, and BioRaCe + S-Apex instruments in simulated canals with an S-shaped curvature.
Methods: Canal transportation and aberrations were assessed by comparing the preinstrumentation and postinstrumentation images under a stereomicroscope. Analysis of variance and post hoc Student-Newman-Keuls test were used for statistical analysis.
Results: ProTaper instruments caused more pronounced canal transportation in the apical curvature (P < .01) than all other instruments. The use of ProTaper, Mtwo, and BioRaCe instruments resulted in more canal aberrations compared with BioRaCe + S-Apex (P < .05).
Conclusions: NiTi systems including less tapered and more flexible instruments like S-Apex seem to be favorable when preparing S-shaped canals.