Title

Fatigue resistance of contemporary rotary instruments is markedly impacted by ambient temperature

Lead Author Affiliation

Advanced Education Program in Endodontology

Second Author Affiliation

Conservative Dentistry

Third Author Affiliation

Endodontics

Introduction/Context

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

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

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.

Comments

This work was supported by a Research Grant by the AAE Foundation (S. Hejlawy). Material support by Dentsply Sirona is gratefully acknowledged.

Location

University of the Pacific, Dugoni Dental School, San Francisco, CA

Format

Poster

Poster Session

Endodontics Residents Presentations

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May 31st, 10:00 AM May 31st, 3:00 PM

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.