الفهرس 
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Abstract
The aim of this study was to evaluate the cyclic fatigue resistance of ProFile GT Series X rotary endodontic files fabricated from M-Wire and compare it to ProFile GT rotary files fabricated from traditional super-elastic Nickel-Titanium alloy.
A total of one hundred and twenty rotary endodontic files, sixty file of each type of file systems were used in this study. Samples were divided into six groups, three for each system according the taper. Each system had three tapers tested 0.04, 0.06, 0.08 all of ISO tip size 30. Furthermore, each group was subdivided into subgroup according to the angle of curvature tested.
A specially designed cyclic fatigue testing device was fabricated for this study. Cyclic fatigue testing was performed by rotating instruments in an artificially constructed stainless steel canals with a 5 mm radius and 45 ̊ and 60 ̊ angle of curvature .The time to failure was recorded, and the total number of cycles to failure was calculated and compared for a total of 120 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 for any defect or deformations observed after testing.
Results:
Overall, there were significant differences in rotary instruments made of different materials (p < 0.001) when tested in the 45 ̊ canal curvature. However, for rotary instruments tested in the 60 ̊ curved canals; the difference was not significant (p > 0.05) of cyclic fatigue life.
However, the results obtained from the test have no correlation with the expected clinical performance of the instruments. It might however, permit a reasonable comparison of the behavior of different instruments types and designs.
Conclusions:
Under the condition of the present study, it can be concluded that:
1- Cyclic fatigue resistance of rotary Nickel-Titanium endodontic instruments is influenced by instrument material and taper as well as the degree of root canal curvature.
2- The effect of instrument taper and the degree of root canal curvature had a higher impact on cyclic fatigue resistance of rotary endodontic instruments than instrument’s material.
3- Predisposition to cyclic fatigue increases with the increase in root canal curvature.
Recommendations:
1. The impact of the new manufacturing technology on other mechanical properties of the rotary endodontic files as well as the clinical performance need further investigations.
2. The need for a standardized model for cyclic fatigue testing both in static and dynamic modes is essential for comparing factors affecting the fracture of rotary endodontic instruments.
1. Walia H., brantely W., Gerstein H. An initial investigation of the bending and torsional properties of Nitinol root canal files. J Endod 1988 July; vol. 14,