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Variable impact by ambient temperature on fatigue resistance of heat-treated nickel titanium instruments

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The purpose of this study was to evaluate the effect of different ambient temperatures on cyclic fatigue (CF) life of two NiTi rotary systems and correlate the results with martensitic transformation temperatures.

Materials and methods

Heat-treated NiTi Vortex Blue (VB) and EdgeSequel Sapphire (SP) instruments (tip sizes no. 20, 25, 30, 35, 40) were tested for CF resistance at room and body temperature (n = 20 each group) in a simulated canal (angle of curvature 60°; radius 3 mm; center from instrument tip 4.5 mm) with a motor controlled by an electric circuit. Mean half-life, beta and eta Weibull parameters were determined and compared. Two further instruments of each brand were subjected to differential scanning calorimetry (DSC).


Temperature had an effect on fatigue behavior: all instruments lasted significantly longer at room than at body temperature. All VB significantly outlasted those of SP at body temperature; while smaller diameters of VB (size no. 20) were also significantly more resistant than SP when tested at room temperature; SP with larger diameters (sizes no. 30, no. 35, and no. 40) lasted significantly longer than VB did.


Immersion in water at body temperature was associated with a marked decrease in the fatigue life of all rotary instruments tested. VB instruments were significantly more CF resistant at body temperature and showed the highest predictability in terms of fracture resistance.

Clinical relevance

Rotary instruments manufactured with different post-machining heat treatment responded differently to changed ambient temperatures. DSC assessment of martensitic conversion temperatures helps to predict the behavior of nickel titanium rotaries in different environments.

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This study was performed in partial fulfillment of the requirements for a MSD degree for Dr. Hejlawy and was supported by the AAE Foundation. Dr. OA Peters serves as a consultant for Dentsply Sirona whose support for this study is also acknowledged.


The work was supported by the AAE foundation.

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Correspondence to Ana Arias.

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Conflict of interest

Dr. Ove Peters serves as a consultant for Dentsply Sirona. The remaining authors declare that they have no conflict of interest.

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This article does not contain any studies with human participants or animals performed by any of the authors.

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For this type of study, formal consent is not required.

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Arias, A., Hejlawy, S., Murphy, S. et al. Variable impact by ambient temperature on fatigue resistance of heat-treated nickel titanium instruments. Clin Oral Invest 23, 1101–1108 (2019).

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