Effect of different axial speed patterns on cyclic fatigue resistance of rotary nickel-titanium instruments

Abstract Background To evaluate the effect of pecking motions with faster upward speed on the dynamic cyclic fatigue resistance of nickel-titanium rotary instruments with different metallurgy. Methods Forty each of ProTaper Universal F3 (PTU) and ProTaper Gold F3 (PTG) instruments (size #30/.09) were equally divided into four groups. The test was performed using an 18-mm-long stainless steel artificial canal with a 5-mm radius of curvature, a 45° canal curvature and a 2-mm canal diameter. A downward speed of 100 mm/min was employed, while the upward speed was set at 100, 150, 200 or 300 mm/min. Time to failure (T f ), number of cycles to failure (N f ) and number of pecking motions to failure (N p ) were recorded. Statistical analysis was performed using Kruskal Wallis and Mann–Whitney U tests for T f , N f, and N p ( α = 0.05). Results The 100/300 mm/min group showed significantly higher N p values than the 100/100 mm/min group ( p < 0.05), whereas there were no significant differences in T f and N f among the tested speed groups ( p < 0.05) in either PTU or PTG. PTG exhibited significantly higher T f , N f, and N p than PTU ( p < 0.05). Conclusions Under the tested conditions, the fastest upward speed group showed significantly higher cyclic fatigue resistance, as demonstrated by larger N p , than the same speed group. PTG had significantly higher cyclic fatigue resistance than PTU in all groups.