Micro-X-Ray Diffraction Study of New Nickel-Titanium Rotary Endodontic Instruments

Background: Next-generation rotary endodontic instruments with improved clinical performance are being fabricated from special superelastic NiTi wires. We are reporting the initial metallurgical study of two recently introduced rotary instruments, HyFlex® CM™ (Coltène Whaledent) and Vortex Blue® (Dentsply Tulsa Dental Specialties), using Micro-X-ray diffraction. A wide range of sizes and tapers was examined, and analyses were performed at five sites on each instrument. Results: Similar x-ray diffraction patterns were observed for both instruments, and no dependence on size and taper was found. The lowest-intensity peaks occurred for the tip region. Four austenite peaks and one martensite peak were evident, along with a lowerangle peak that matched anatase titanium oxide. Preferred orientation existed for both austenite and martensite. Conclusions: Instruments were manufactured by similar proprietary processes. Future metallographic, SEM and TEM observations are needed to characterize instrument microstructures fully, since x-ray diffraction peak intensities are considerably diminished for the work-hardened martensite phase.