Evaluation of mechanical properties of coronal flaring nickel-titanium instruments

Abstract Background: The aim of this study was to evaluate the bending and torsional resistance of the following instruments: Mtwo 25.07, Navigator W-XN, ProTaper SX, MK Orifice Shapper and MK Sequence 17.12. Methods: One hundred instruments were used (n=20). Resistance to bending (n=10), torque and angular deflection (n=10) at the failure of new instruments were measured according to ISO 3630-1. The fractured surface of each fragment was examined by scanning electron microscopy (SEM). Data were analyzed using 1-way analysis of variance and Tukey tests. Results: Torsional resistance values of MK Sequence were higher than the other groups (P.05) and ProTaper SX, which presented the lowest values (P<.05). Mtwo 25.07 showed the highest angular deflection (P.05). ProTaper SX and MK Orifice Shapper also showed no significant differences (P>.05). MK Sequence 17.12 instruments had the lowest angular deflection values (P<0.5). There were significant differences among all the groups in bending stiffness test (P<.05), but ProTaper SX had the lowest torque to bend (P<.05). MK Sequence 17.12 presented the larger cross-sectional area at 3mm from the tip. SEM analysis showed similar and typical features of torsional failure for all instruments tested.Conclusions: In conclusion MK Sequence 17.12 had the highest torsional fracture resistance. Mtwo 25.07 showed higher angular deflection capacity, and ProTaper SX the lower bending stiffness.