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  • Title: Mechanical behavior at different temperatures and stresses for superelastic nickel-titanium orthodontic wires having different transformation temperatures.
    Author: Iijima M, Ohno H, Kawashima I, Endo K, Mizoguchi I.
    Journal: Dent Mater; 2002 Jan; 18(1):88-93. PubMed ID: 11740969.
    Abstract:
    OBJECTIVE: The purpose of this study was to investigate the mechanical properties of superelastic nickel-titanium orthodontic wires under controlled stress and temperature. METHODS: Three different superelastic nickel-titanium wires were examined using differential scanning calorimetry (DSC), three-point bending test and micro X-ray diffraction (micro-XRD). The three-point bending test was carried out at constant temperature (23, 37 and 60 degrees C) and stepwise temperature changes (37-60 degrees C and to 37 degrees C) (37-2 degrees C and to 37 degrees C). Five specimens of each wire were tested. Micro-XRD spectra were measured at the tension side of the wire when the temperature changed from 37 to 60 degrees C or 2 degrees C. RESULTS: The load during the stepwise temperature changes (37-2 degrees C and to 37 degrees C) was consistent with that measured at a corresponding constant temperature. The micro XRD spectrum clearly showed that the austenite phase was transformed to martensite phase when the temperature is decreased from 37 to 2 degrees C. In a stepwise temperature change (37-60 degrees C and to 37 degrees C), the load became higher than the original load at each corresponding constant temperature. However, there was no detectable change in the micro-XRD spectrum when the temperature was increased from 37 to 60 degrees C. SIGNIFICANCE: The superelastic nickel-titanium wires exhibited complicated and unexpected mechanical properties under stepwise temperature change. This study shows the possibility of qualitative analysis using micro-XRD to understand mechanical properties of these nickel-titanium wires.
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