الفهرس 
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Abstract
Summary
The purpose of this study is to evaluate the effect of Sodium hypochlorite irrigant on the cyclic fatigue resistance of two different rotary files of constant radius under two canal curvatures, 45 and 60 degrees.
A total of 64 files with 0.025 mm tip diameter and taper 6% will be selected for study and will be divided into two main groups according to the type of file into: group I (32 files) (W3-pro) (F1), group II (32 files) (Revo-s) (F2), Each group is further divided into 2 subgroups according to irrigation; Subgroup A (saline irrigation -16 files), Subgroup B (sodium hypochlorite -16 files), The files of each subgroup will be immersed in the selected irrigant for 5 minutes before testing.
All instruments were inspected by using an optical microscope with 20X magnification for morphologic analysis and for any signs of visible deformation. All defective instruments were discarded. Then files were divided into 2 main groups each of 32 files that were again subdivided into 2 subgroups of 16 files.
A specific stainless-steel block was used to bear friction, containing an artificial canal of 45° curvature and 5 mm concave-tempered steel radius, which incorporated a notched V-form for guiding the instruments, the artificial Canal were manufactured by reproducing the instrument’s size and taper. The block was fixed, and instruments were inserted with their points at the end of the curve and rotated. All instruments of the groups were rotated until fracture occurred.
Whilst maintaining conditions close to the clinical situations, A custom made cyclic fatigue apparatus will be designed for this study and used to hold the testing block and the hand piece that will be rotated at the recommended RPM for each file type at standardized fixed distance.
Evaluation of Cyclic fatigue testing using time to fracture, and the length of the broken fragment were recorded and tabulated for all groups. SEM of the fractured instruments; Representative samples from all the previous groups of files were prepared for SEM examination to detect mode of fracture and evaluate the presence of any change after the fracture.
Comparison between different groups (IA and IB) at 60 degrees and 45 degrees showed that; group IA 60 degrees of curvature and group IB 60 degrees of curvature were significantly the highest, while group IA and IB 45 degrees of curvature revealed no fracture up to 10 minutes of rotation. group IA 45 degrees of curvature was significantly the highest, then group IB 45 degrees of curvature, then group IA 60 degrees of curvature, while group IB 60 degrees of curvature was significantly the lowest.
group I and II at both curvatures 60 degrees and 45 degrees showed that A 60 degrees: group I was significantly higher than group II. 45 degrees: group I (no fracture) was significantly higher than group II. B 60 degrees: group I was significantly higher than group II. B 45 degrees: group I (no fracture) was significantly higher than group I. In conclusion, Immersion of rotary files made of different alloys in sodium hypochlorite for 10 min had no effect on their fracture resistance.