Comparison of the cyclic fatigue resistance of nickel-titanium rotary instruments manufactured using controlled memory wire

Aim: The purpose of this study was to evaluate the impact of three controlled memory files ( Hyflex CM (HCM) , Hyflex EDM(HEDM) , One Curve(OC) ) on cyclic fatigue resistance compared to shape memory files (2Shape(2S), Protoper gold(PTG)).
Materials and methods: A total of 50 files were rotated in simulated stainless steel curved canals reproducing size and taper of the files with 45 angle of curvature and 5mm radius of curvature. The time to fracture (TTF) was recorded in seconds, the number of cycles to fracture was calculated (NCF) and the length of the fractured fragments was measured .Data was statistically analysed using IBM SPSS software package version 20.0. Quantitative data were described using mean and standard deviation for parametric data after testing normality using Kolmogrov-Smirnov test. Significance of the obtained results was judged at the 5% level.
Results: When comparing the TTF of all the tested files the data obtained from statistical analysis showed that the resistance to cyclic fatigue of tested files arranged from highest to lowest was  HEDM ,HCM ,PTG ,2S and OC respectively .When the NCF values were taken into consideration HEDM  and HCM reported a significant higher cyclic fatigue resistance than PTG (p < 0.05) , OC and 2S reported the lowest resistance to cyclic fatigue among the tested files with no significant difference between OC and 2S(p>0.05) .There was no significant difference between PTG and OC when comparing NCF (p>0.05). No significant difference was found in the length of the fractured fragments (p > 0.05).