الفهرس 
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Abstract
Summary
This study aimed to compare the cyclic fatigue resistance of three NiTi rotary systems (RaCe, 2Shape, M-pro) at the room and body temperatures. As well, the phase transformation of the tested instruments was investigated using differential scanning calorimetry
Total of sixty files #25 .06 of these brands were selected for the study, Cyclic fatigue testing was done using a dynamic cyclic fatigue testing device along with a custom made artificial stainless-steel canal that had 60° and 3mm radius of curvature. There were three groups divided according to the file type (n=20). Each group was subdivided into 2 subgroups according to the temperature during the test: Subgroup 1 (room temperature 22 ± 0.5°C) and Subgroup 2 (body temperature 37 ± 0.5°C). Samples were rotated continuously in an axial motion until fracture in the artificial canals to simulate clinical conditions.
Five test specimens of RaCe, 2Shape, and M-pro all of the size #25 .06 were investigated using differential scanning calorimetry.
Results showed that generally, the 2Shape file showed the highest cyclic fatigue resistance followed by the M-pro file and the least fatigue resistance was the RaCe file. At room temperature, there was a highly significant difference between the three files. While at the body temperature the 2Shape file and the RaCe file were significantly different but there was no significant difference between the 2Shape and the M-pro.
On the other hand, the effect of temperature change on the cyclic fatigue of the three files showed that the rise in the temperature is accompanied by a decrease in the cyclic fatigue resistance of the RaCe and the 2Shape files. While it did not affect the fatigue resistance of M-pro file
For the DSC curves, The RaCe and the 2Shape files did not show austenitic transformation in the temperature range evaluated in this study. On the contrary, for the M-pro file a single endothermic peak on the heating curve was detected, with an onset temperature of 35.77°C and an enthalpy change (ΔH) of 1.676 J/g, corresponds to the transformation from martensitic NiTi to austenitic NiTi.
Conclusions
Within the limitations of this in vitro study, the following conclusions could be drawn:
• T-wire and CM-wire NiTi files technologies have a significant effect on cyclic fatigue which varies according to the technology.
• The environmental temperature plays a key role in the fatigue behavior.
Recommendations
• Further investigations are needed to evaluate the mechanical properties of new heat-treated NiTi alloys.
• Further investigations to develop and fully understand the mechanism of NiTi heat treatments.
•Further investigations on the influence of different temperatures on the mechanical properties of the different instruments and the different metal treatments of the NiTi alloy.
• Future cyclic fatigue studies should be conducted at body temperature.