Objective: To evaluate the torsional and cyclic fatigue behavior of post-machining heat-treated K3XF and conventional K3 nickel titanium (NiTi) instruments.
Methodology: New K3XF and K3 files size 25/0.04 (n = 15) were tested in torsion and fatigue tests until fracture to determine the mean number of cycles to failure (NCF) and torque to failure. The cyclic torsional loading experiment was conducted; K3XF and K3 files (n = 30 in each group) were programmed to repeatedly rotate from zero angular deflection to 180° and then return to zero torque. Each rotation was defined as one cycle. Each file was subjected to 10 cycles of torsional loading. Fifteen files from each group were subsequently tested in torsion until fracture. Also, fifteen files subjected to cyclic torsional loading were examined using a three-point bending apparatus to obtain the mean number of cycles to failure. The fracture surface was examined with a scanning electron microscope. The crack-initiation sites and the percentage of dimple area of the whole fracture cross-sectional area were recorded.
Results: There was no statistically significant difference between the new K3 and K3XF instruments in the maximum torque or maximum angular deflection. For the previously cycled files, K3XF demonstrated higher torque at fracture values than K3 Instruments (P < .05). The fatigue resistance of K3XF was significantly higher than K3 in both the new and previously cycled groups (P < .05). The NCF value of K3XF with torsional loading was even higher than that of K3 files without torsional loading, although there was no significant difference. New K3XF files demonstrated a significantly higher NCF than previously cycled files (P < .05).
Conclusions: Cyclic torsional loading decreased the cyclic fatigue resistance of K3XF and K3 instruments although it did not affect their torsional properties. K3XF demonstrated better cyclic fatigue resistance than K3 for both new and previously torqued files.Dentistry, Faculty ofGraduat
