Shaping ability of five continuous rotary nickel-titanium instruments in multi-curved root canals: an ex vivo study based on simulated resin blocks

Abstract Background: The aim of this study was to comparatively evaluate the shaping ability of five continuous rotary nickel-titanium instruments when preparing root canals exhibiting multiple curvatures. Methods: A total of 60 resin-simulated S-shaped root canals (coronal curve; 22°-23° curvature, 5 mm radius and apical curve; 21°-22° curvature and 4 mm radius) were divided into five groups (n=12). The root canals were prepared one of the following five Ni-Ti alloy instruments: Mtwo, Mtwo Blue, Protaper Next, Hyflex CM and Twisted File to the size/taper at 25#/.06. One-way analysis of variance was used for the statistical analysis, with a significance threshold of p<0.05. Results: Instrument fractures and procedural preparation errors were not observed during canal preparation. Regarding canal deviation and centering ability, the use of Mtwo instruments resulted in a significantly higher deviation and weaker centering ability than the other four groups (p<0.05). At some measurement points, the Twisted File and Hyflex CM showed significantly smallest deviation in the tested instruments (p < 0.05). Conclusion: Within the limitations of this study, all instruments performed well, and the Twisted File and Hyflex CM instruments demonstrated a particularly strong shaping ability in resin-simulated S-shaped root canals.