Microscopic Features of Fractured Fragment of Nickel-Titanium Endodontic Instruments by Two Different Modes of Torsional Loading

Table 1

Comparison of torsional resistance (mean ± SD) by the two methods.

Test method	RTL method	STL method
File	NRCF	Ultimate strength (N⋅cm)
V-Taper 2	5454 ± 1790	1.70 ± 0.19
HyFlex EDM	2373 ± 820	1.35 ± 0.16
ProTaper Next	855 ± 237	0.83 ± 0.05

superscript letters indicate significant differences between groups in vertical column (). RTL: repetitive torsional loading; STL: single continuous torsional loading; NRCF: number of repetitive load cycles until fracture.