Micro-XRD and temperature-modulated DSC investigation of nickel-titanium rotary endodontic instruments.
OBJECTIVE
Employ Micro-X-ray diffraction and temperature-modulated differential scanning calorimetry to investigate microstructural phases, phase transformations, and effects of heat treatment for rotary nickel-titanium instruments.


METHODS
Representative as-received and clinically used ProFile GT and ProTaper instruments were principally studied. Micro-XRD analyses (Cu Kalpha X-rays) were performed at 25 degrees C on areas of approximately 50 microm diameter near the tip and up to 9 mm from the tip. TMDSC analyses were performed from -80 to 100 degrees C and back to -80 degrees C on segments cut from instruments, using a linear heating and cooling rate of 2 degrees C/min, sinusoidal oscillation of 0.318 degrees C, and period of 60s. Instruments were also heat treated 15 min in a nitrogen atmosphere at 400, 500, 600 and 850 degrees C, and analyzed.


RESULTS
At all Micro-XRD analysis regions the strongest peak occurred near 42 degrees , indicating that instruments were mostly austenite, with perhaps some R-phase and martensite. Tip and adjacent regions had smallest peak intensities, indicative of greater work hardening, and the intensity at other sites depended on the instrument. TMDSC heating and cooling curves had single peaks for transformations between martensite and austenite. Austenite-finish (A(f)) temperatures and enthalpy changes were similar for as-received and used instruments. Heat treatments at 400, 500 and 600 degrees C raised the A(f) temperature to 45-50 degrees C, and heat treatment at 850 degrees C caused drastic changes in transformation behavior.


CONCLUSIONS
Micro-XRD provides novel information about NiTi phases at different positions on instruments. TMDSC indicates that heat treatment might yield instruments with substantial martensite and improved clinical performance.
Alapati
Satish B
SB
Department of Materials Science, College of Dental Medicine, Medical University of South Carolina, Charleston, SC, USA.
Brantley
William A
WA
Iijima
Masahiro
M
Schricker
Scott R
SR
Nusstein
John M
JM
Li
Uei-Ming
UM
Svec
Timothy A
TA
D002152:Calorimetry, Differential Scanning / Q000379:methods*; D003080:Cold Temperature; D003460:Crystallization; D003722:Dental Alloys / Q000737:chemistry*; D006358:Hot Temperature; D006801:Humans; D008422:Materials Testing; D009532:Nickel / Q000737:chemistry*; D009584:Nitrogen / Q000737:chemistry; D018915:Root Canal Preparation / Q000295:instrumentation*; D013499:Surface Properties; D013997:Time Factors; D014025:Titanium / Q000737:chemistry*; D014961:X-Ray Diffraction / Q000379:methods*
D003722:Dental Alloys; C040654:titanium nickelide; C093824:Martensite; C093826:Austenite; D009532:Nickel; D014025:Titanium; D009584:Nitrogen