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Fatigue of Dental High-Speed, Air-Driven Handpiece by Steam Sterilization


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Autoclaving dental high-speed, air-driven handpieces (HPs) is a recommended standard for infection prevention and control. Subjection to repeated sterilization may cause fatigue, and possible corrosion, for most HP mechanics. Objective: The purpose of this study was to evaluate the effect of steam sterilization on the mechanical properties of HPs and to determine whether sterility inside the HP lumen can be maintained after thermal cyclic fatigue induced by repeated sterilization. Methods: Six commercially available brands of HPs (n = 6/brand) were selected: TiMax-Z (NSK), Mastertorque-miniLux (Kavo), Experttorque-Lux (Kavo), Midwest Tradition Pro-TBF (Dentsply), Midwest Phoenix ZRK (Dentsply), and Midwest Stylus Plus-SPK (Dentsply). The HPs were subjected to 180 cycles of gravity displaced sterilization without lubrication to accelerate the effect of fatigue aging. The HPs were exposed to nonsterile conditions prior to each sterilization cycle and then sterilized (Tuttnauer 2540EKP). Bacterial loads were quantified at the initial, 60th, 90th, 120th, and 180th sterilization cycles only. Using a custom-made universal testing machine (ACUMEN, MTS), HP fatigue parameters such as stall torque, power, and revolution per minute (RPM) were measured. Data were analyzed with repeated measures ANOVA/Tukey (=0.05). Results: Experttorque-Lux, Mastertorque-mini-Lux, Midwest Phoenix ZRK, Midwest Stylus Plus-SPK, and TiMax-Z maintained similar power as baseline over 180 cycles of steam sterilization. MidwestTradition Pro-TBF demonstrated the greatest loss in power (20%) and RPM (18%) over 180 cycles than all other five brands, but still maintained the greatest power. After 120 cycles of repeated sterilization without lubrication, one Midwest Tradition Pro-TBF HP experienced mechanical failure and was excluded from further testing. No signs of corrosion or fractures were noted.



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