Date of Award
Master of Science (MS)
Introduction: Nickel-Titanium (NiTi) files have become popular in endodontic procedures compared to traditional stainless steel hand files owing to their increased flexibility which is especially advantageous in curved canals. Due to the associated costs, endodontic instruments are frequently re-used, which requires sterilization between uses. With the application of temperature NiTi has the ability to undergo phase transformations, altering the properties of the instruments. The purpose of this study was to investigate phase transformations of four brands of NiTi rotary endodontic instruments in the as-received condition and after multiple sterilization cycles under steam sterilization, using differential scanning calorimetry. Materials and Methods: Four brands of nickel-titanium endodontic rotary files size 35, .04 taper were evaluated in this study: ProFile (Dentsply Tulsa Dental Specialties, Tulsa, OK), ProFile Vortex (Dentsply), Vortex Blue (Dentsply), and HyFlex CM (Coltène/Whaledent, Cuyahoga Falls, OH). The transformation temperatures and phase transformations of these files were determined in the as-received condition and after 1, 3, and 5 cycles of steam sterilization by differential scanning calorimetry. Measurements were analyzed using a two-way ANOVA. Results: There were significant differences between file brands in austenite finish temperature (p < 0.05) but the only statistical significant differences in thermal properties when comparing files before and after 1, 3, and 5 cycles of steam sterilization were found with onset heating (p < 0.05). Conclusion: Repeated cycles of steam sterilization do not appear to influence the phase transformations of NiTi endodontic instruments.