الفهرس 
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Abstract
The aim of the study was to evaluate the effect ofautoclaving and curvature severity on Mpro,2Shape and Revo-s systems.
Total of ninty six files #25 with 6% of these brands were selected for the study, Cyclicfatigue testing was done using acyclic fatigue testing device along with a custommade artificial stainless steelcanals which had 60° and 3mm radius of curvature, and 45° and 5mm radius of curvature. There was three groups, each(n=32). Each groupwas subdivided into 2 subgroups according to sterilization:Subgroup a (non-sterilized) and Subgroup b (Sterilized for 5 cycles), each subgroup was further subdivided into two subdivisions according to the curvature and radius :Subdivision 1 (in the canal of 60° curvature and radius 3 mm.) and Subdivision 2 (in the canal of 45° curvature and radius 5 mm.) samples were rotated continuously until fracture in the artificial canals under body temperature to simulate clinical conditions.
Results showed that in the mild curvature Mpro group hasthe highest fatigueresistance,followed by 2Shape group, and the least fatigue resistance was for Revo-s groups. While inn the sever curvature 2Shape group hasthe highest fatigueresistance, followed by Revo-s group, and the least fatigue resistance was for Revo-s groupsTesting protocol did not showany significant difference between Revo-s with autoclaving and Revo-s without autoclaving, however it showed significant difference between Mpro Withautoclaving and Mpro without autoclaving, also it showed significant difference between 2Shape with autoclaving and 2Shape with autoclaving
Mpro without autoclaving had lower fatigue resistancethan MproWith autoclaving, while 2Shape without autoclaving had higher fatigue resistance than 2Shape with autoclaving, This (within the limitationof the study) confirmed autoclaving to have positive effecton fatigue resistance of Mpro, negative effect on fatigue resistance of 2Shape. However for Revo-s ,autoclaving had no significant effect.
Conclusions
Under the conditions of the present study, the followingconclusions could be drawn:
• T-wire and CM-wire NiTi files technologies havesignificant effect on cyclic fatigue which variesaccording the technology.
• The effect of autoclaving on cyclic fatigue is notidentical for all NiTi files.
• Curvature severity inversely affect fatigue resistance.
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Recommendations:
• Further investigations are needed to evaluatemechanical properties of new heat treated NiTi alloys.
• Further investigations to develop and fully understandthe mechanism of NiTi heat treatments.
• Further investigations on the interaction betweencyclic