Characterization of Next-Generation Nickel-Titanium Rotary Endodontic Instruments

Background: Next-generation rotary endodontic instruments (GT® Series X™) with improved clinical performance have been fabricated from special superelastic NiTi wire with a nanoscale martensitic structure. Last year we reported Vickers hardness measurements and SEM images of as-received and clinically used GT® Series X™ instruments. In this manuscript, we report characterization of the nickel-titanium instruments, using Micro-X-ray diffraction and differential scanning calorimetry (DSC). Results: X-ray diffraction shows evidence of the martensitic structure that accounts for the much higher Vickers hardness and superior wear resistance of the next-generation NiTi instruments, compared to previous instruments. DSC analyses show that fabrication of these instruments from the starting special superelastic wire has little effect on NiTi transformations and that most of the NiTi microstructure does not undergo transformation during heating to 120°C. Conclusions: Micro-X-ray diffraction and DSC provide important characterization information for these instruments, but TEM is needed for detailed insight the complex martensitic structure.