Effects of Raw Material and Rotational Speed on the Cyclic Fatigue of ProFile Vortex Rotary Instruments

Abstract

Introduction This in vitro study compared the cyclic fatigue resistance of ProFile Vortex rotary instruments (DENTSPLY Tulsa Dental, Tulsa, OK) made of two different raw materials: M-Wire and regular superelastic wire (SE-wire) at two different rotational speeds. Two rotary-based Profile Vortex instruments with taper 0.04 and 0.06 (25 mm in length and #30 in size) were compared. Methods Cyclic fatigue testing was performed by rotating instruments in an artificially constructed stainless steel canal with a 5-mm radius and a 90° angle of curvature at two different test frequencies: 300 and 500 rpm. The time to failure was recorded, and the total number of cycles to failure was calculated and compared for a total of 160 samples. Statistical analysis was performed with one-way analysis of variance and the Tukey test for individual comparisons (confidence level of p < 0.05). Fracture surfaces of broken instruments were also observed under scanning electron microscopy. Over 50% of broken files made of SE-wire exhibited multiple crack initiation sites compared with the single crack initiation on files made of M-Wire. Results Overall, there were significant differences in rotary instruments made of different materials ( p < 0.001). However, for rotary instruments made from the same material (either M-Wire or SE-wire), there was no significant difference ( p > 0.05) of cyclic fatigue life under different rotational speeds (300 and 500 rpm). Conclusions ProFile Vortex files made of M-Wire exhibited superior cyclic fatigue resistance (∼150% longer in fatigue life) compared with those made of regular SE-wire at two test frequencies (300 and 500 rpm).