الفهرس 
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Abstract
The aim of the study was to evaluate the effect of zero, two and five cycles of autoclave sterilization on the dynamic cyclic fatigue resistance of R Motion files and PTN files at body temperature. And used scanning electron microscopy to investigate the mode of fracture and surface features of each subgroup. The corresponding phase transformation for each subgroup was recorded using differential scanning calorimetry. A Total of 56 files size 25 taper 6% of each brand were selected for the study. Cyclic fatigue testing was done using a dynamic testing device along with a custom-made artificial SS canal which had 60° and 5mm radius of curvature. There were two main groups each (n=28). Each group was subdivided into four subgroups according to number of sterilization cycles: Subgroup N (negative control), subgroup Z (zero cycles), Subgroup T (two cycles) and Subgroup F (five cycles). Samples were rotated continuously until fracture in the artificial canal. The NCF and TTF were calculated. SEM was performed on three samples for each subgroup. Phase transformation temperatures for subgroups Z, T and F were analyzed using DSC.
Results showed that sterilization increased DCFR of R Motion files and had no effect on DCFR of PTN files. DCFR of R Motion file was higher than PTN file. SEM of all files showed ideal morphological appearance of ductile fracture. DSC analysis of R Motion file subgroups showed two transformation peaks, one on cooling and the other on heating the sample. While DSC of PTN file subgroups showed no peaks on heating or cooling.