OBJECTIVES: The purpose of this study was to investigate the effect of autoclave sterilization technique on the structure and surface hardness of some hand-driven Ni-Ti endodontic files. MATERIALS AND METHODS: Two brands of Ni-Ti files were selected for this study. A total of 40 Ni-Ti #25 K-type files were divided into 2 groups of 20 each representing the two brands. Three subgroups of 5 each were sterilized in increments of two-cycle autoclave. One subgroup was retained as control. X-ray diffraction (XRD) and differential scanning colorimetric (DSC) techniques were utilized to characterize the files structure. The surface hardness of the tested files was also evaluated using Vickers microhardness tester. In addition, the file samples were chemically etched to reveal the changes in the microstructure using scanning electron microscope (SEM). RESULTS: The obtained x-ray patterns and the DSC plots indicated that the analyzed files had the superelastic property with an austenitic-finish temperature (A) of about 50°C. In general, the temperature range and the phase transformation behavior were similar for the two tested files; before and after sterilization. In as-received condition, Vickers hardness values were 288±15 and 276±12 (kg/mm) for UlraFlex and Nitiflex files respectively. No significant differences (p>0.01) were found in the hardness values of files after sterilization. The microstructure of the tested files remained almost unchanged after being sterilized. CONCLUSIONS: The findings of this study indicate that the performed autoclave sterilization method does not significantly affect the structure, hardness or microstructure of Ni-Ti files. The detected slight variations between the two investigated file brands might be attributed to manufacturing processes and quality control procedures.
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