Phase transformation changes in thermocycled nickel-titanium orthodontic wires.
OBJECTIVE
In the oral environment, orthodontic wires will be subject to thermal fluctuations. The purpose of this study was to investigate the effect of thermocycling on nickel-titanium (NiTi) wire phase transformations.


METHODS
Straight segments from single 27 and 35 degrees C copper NiTi (Ormco), Sentalloy (GAC), and Nitinol Heat Activated (3M Unitek) archwires were sectioned into 5mm segments (n=20). A control group consisted of five randomly selected non-thermocycled segments. The remaining segments were thermocycled between 5 and 55 degrees C with five randomly selected segments analyzed with differential scanning calorimetry (DSC; -100<-->150 degrees C at 10 degrees C/min) after 1000, 5000, and 10,000 cycles. Thermal peaks were evaluated with results analyzed via ANOVA (alpha=0.05).


RESULTS
Nitinol HA and Sentalloy did not demonstrate qualitative or quantitative phase transformation behavior differences. Significant differences were observed in some of the copper NiTi transformation temperatures, as well as the heating enthalpy with the 27 degrees C copper NiTi wires (p<0.05). Qualitatively, with increased thermocycling the extent of R-phase in the heating peaks decreased in the 35 degrees C copper NiTi, and an austenite to martensite peak shoulder developed during cooling in the 27 degrees C copper NiTi.


CONCLUSIONS
Repeated temperature fluctuations may contribute to qualitative and quantitative phase transformation changes in some NiTi wires.
Berzins
David W
DW
Dental Biomaterials, School of Dentistry, Marquette University, 113A Wehr Physics Building, P.O. Box 1881, Milwaukee, WI 53201, USA. david.berzins@marquette.edu
Roberts
Howard W
HW
D000704:Analysis of Variance; D002152:Calorimetry, Differential Scanning; D003300:Copper; D003722:Dental Alloys / Q000737:chemistry*; D003799:Dental Stress Analysis; D004548:Elasticity; D006358:Hot Temperature; D008422:Materials Testing; D009532:Nickel / Q000737:chemistry*; D009969:Orthodontic Wires; D044367:Phase Transition; D018709:Statistics, Nonparametric; D014025:Titanium / Q000737:chemistry*
D003722:Dental Alloys; C040654:titanium nickelide; C093824:Martensite; D003300:Copper; D009532:Nickel; D014025:Titanium