الفهرس 
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Abstract
Cyclic fatigue resistance was evaluated and compared by different nickel-titanium rotary systems under continuous rotation and reciprocating motion. One hundred and twenty eight readymade resin blocks have 450 angle of curvature were used. Files were randomly classified into 4 groups each of 32 according to the type of instrument that used for preparation of simulated canals.
group P: resin blocks were prepared using protaper F2 file. ”Conventional NiTi”
group T: resin blocks were prepared using twisted file. ”R-phase”. group R: resin blocks were prepared using reciproc file. ”M-wire”. group H: resin blocks were prepared using hyflex file. ”CM-wire”.
Each group subdivided into 2 subgroups each of 16 according to the type of motion used:
Subgroup I: continuous rotation motion.
Subgroup II: reciprocation motion.
Each subgroup divided into two divisions according to type of irrigation used:
Division a: samples irrigated with 5ml distilled water.
Division b: samples irrigated 5ml NaOCl5.25%.
After complete instrumentation of the artificial canals up to full working length according to manufacturer instructions. Files were
confirmed to be adjusted at working length then introduced to the artificial canals and kept working till fracture. Time to fracture was measured utilizing digital stopwatch. Randomly selected broken files ”n=2” from each group were examined utilizing scanning electron microscope. The data were tabulated and subjected to statistical analysis.
The results of the present study showed that the reciprocation motion more cyclic fatigue resistance than rotation motion, reciproc file showed more resistance to cyclic fatigue than twisted and protaper F2 files, no significant difference between reciproc and hyflex files and there is reduction in cyclic fatigue resistance when using sodium hypochlorite than when using water irrigating solutions.