Mechanical behavior at different temperatures and stresses for superelastic nickel-titanium orthodontic wires having different transformation temperatures.
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.


CONCLUSIONS
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.
Iijima
M
M
Department of Orthodontics, School of Dentistry, Health Sciences University of Hokkaido, Kanazawa 1757, Ishikari-Tobetsu, 061-0293, Hokkaido, Japan. iijima@hoku-iryo-u.ac.jp
Ohno
H
H
Kawashima
I
I
Endo
K
K
Mizoguchi
I
I
D002152:Calorimetry, Differential Scanning; D003080:Cold Temperature; D003300:Copper / Q000737:chemistry; D018360:Crystallography, X-Ray; D003722:Dental Alloys / Q000737:chemistry*; D004548:Elasticity; D006358:Hot Temperature; D006801:Humans; D008422:Materials Testing; D019563:Mechanics; D008832:Microchemistry; D009532:Nickel / Q000737:chemistry*; D009969:Orthodontic Wires; D018583:Pliability; D013314:Stress, Mechanical; D013696:Temperature; D014025:Titanium / Q000737:chemistry*
C415948:Copper NiTi; D003722:Dental Alloys; C040654:titanium nickelide; C093824:Martensite; C093826:Austenite; D003300:Copper; D009532:Nickel; D014025:Titanium