الفهرس 
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Abstract
The purpose of the present study was to evaluate the cyclic fatigue of three different rotary nickel titanium files Nitishaper, Hyflex EDM and Mpro in continues rotation.
A total of 48 rotary files were used in this study. They were classified into the following groups: group A: Nitishaper Ni-Ti files, has the tip ISO size 25, (16 files). group B: Hyflex EDM Ni-Ti files, has the tip ISO size 25, (16files). group C Mpro Ni-Ti files has the tip ISO size 25, (16 files) then each group was further sub divided into two equal sub- groups according to the tested radii and angle of curvature:
• Sub group 1: 2mm radius of curvature and 45° angle of curvature.
• Sub group 2: 5mm radius of curvature and 45° angle of curvature.
A custom made stainless steel cyclic fatigue apparatus was especially designed for this study and a specially fabricated metal block made of stainless steel was used in this test.
The metal block contains two artificial canals 2mm in depth were designed to accommodate each instrument in terms of size and taper, thus providing the instrument with a suitable trajectory.
One of the two canal has 2mm Radius of curvature with angle of curvature 45° and the other 5mm radius of curvature with 45° angle of curvature.
All instruments were rotated until fracture occurred and the time to fracture was recorded and number of cycles for fracture was calculated. Means and standard deviations of NCF were calculated for each system and data were subjected to 2-way anova (p<0.05).
Result were tabulated and statistically analyzed. The result showed that regardless to the radius of curvature Hyflex EDM had a statistically significant more number of cyles to be fractured than Nitishaper and Mpro.