Fatigue resistance of contemporary rotary instruments is markedly impacted by ambient temperature
Introduction/Context/Diagnosis
Endodontic instruments may fracture during treatment and in vitro studies have been performed previously to determine instruments life span. Until recently such studies were performed at room temperature, while it is known that temperature effects the martensitic transformation of the instruments and hence the physical properties of the files. Therefore, the purpose of this study was to evaluate the effect of 2 different temperatures (21ºC and 37ºC) on the cyclic fatigue life of three different types of contemporary NiTi rotary instruments and correlate the results with martensitic transformation temperatures.
Methods/Treatment Plan
Nickel-titanium rotary instruments (n = 40 of each tip size #20, 25, 30, 35, 40 (Vortex Blue; Dentsply Sirona Inc.), EdgeSequel Sapphire and EdgeFile X7 (both by Edgendo Inc.) were tested for cyclic fatigue in a water bath at room temperature (20ºC, N=20 of each tip size) and at body temperature (37ºC, N=20 of each tip size). Instruments were rotated until fracture occurred in a simulated canal with an angle of curvature of about 60º and a radius of curvature of 3mm; the center of the curvature was 4.5mm from the instrument tip. The number of cycles to fracture was determined using a stopwatch. Phase transformation temperatures for each brand were analyzed by differential scanning calorimetry (DSC). Data were analyzed using Weibull analysis.
Results/Outcome
All instruments lasted significantly longer when tested at room than at body temperature. All tested diameters of Edge X7 instruments will significantly outlast those corresponding of Edge Sapphire and Vortex Blue instruments at both temperatures. All Vortex Blue instruments significantly outlasted those of Edge Sapphire at body temperature, but when tested in room temperature Edge sapphire sizes #30, 35, and 40 lasted significantly longer than corresponding Vortex Blue instruments; there were no significant differences for instruments # 25. For size #20, Vortex Blue lasted longer than Edge Sapphire in room temperature as well. This behavior correlated well with DSC data.
Significance/Conclusions
Under the conditions of this study, using a novel testing design, immersion in water at simulated body temperature was associated with a marked decrease in the fatigue life of all contemporary rotary instruments tested.
Location
University of the Pacific, Dugoni Dental School, San Francisco, CA
Format
Poster
Poster Session
Endodontics Residents Presentations
Fatigue resistance of contemporary rotary instruments is markedly impacted by ambient temperature
University of the Pacific, Dugoni Dental School, San Francisco, CA
Endodontic instruments may fracture during treatment and in vitro studies have been performed previously to determine instruments life span. Until recently such studies were performed at room temperature, while it is known that temperature effects the martensitic transformation of the instruments and hence the physical properties of the files. Therefore, the purpose of this study was to evaluate the effect of 2 different temperatures (21ºC and 37ºC) on the cyclic fatigue life of three different types of contemporary NiTi rotary instruments and correlate the results with martensitic transformation temperatures.
Comments/Acknowledgements
This work was supported by a Research Grant by the AAE Foundation (S. Hejlawy). Material support by Dentsply Sirona is gratefully acknowledged.