3D Finite Element Analysis of Rotary Instruments in Root Canal Dentine with Different Elastic Moduli

João Paulo Mendes Tribst,Fausto Zamparini,Alexandre Luiz Souto Borges,Carlo Prati,Pietro Ausiello,Maurizio Ventre,Amanda Maria De Oliveira Dal Piva

doi:10.3390/app11062547

Abstract

The aim of the present investigation was to calculate the stress distribution generated in the root dentine canal during mechanical rotation of five different NiTi endodontic instruments by means of a finite element analysis (FEA). Two conventional alloy NiTi instruments F360 25/04 and F6 Skytaper 25/06, in comparison to three heat treated alloys NiTI Hyflex CM 25/04, Protaper Next 25/06 and One Curve 25/06 were considered and analyzed. The instruments’ flexibility (reaction force) and geometrical features (cross section, conicity) were previously investigated. For each instrument, dentine root canals with two different elastic moduli(18 and 42 GPa) were simulated with defined apical ratios. Ten different CAD instrument models were created and their mechanical behaviors were analyzed by a 3D-FEA. Static structural analyses were performed with a non-failure condition, since a linear elastic behavior was assumed for all components. All the instruments generated a stress area concentration in correspondence to the root canal curvature at approx. 7 mm from the apex. The maximum values were found when instruments were analyzed in the highest elastic modulus dentine canal. Strain and von Mises stress patterns showed a higher concentration in the first part of curved radius of all the instruments. Conventional Ni-Ti endodontic instruments demonstrated higher stress magnitudes, regardless of the conicity of 4% and 6%, and they showed the highest von Mises stress values in sound, as well as in mineralized dentine canals. Heat-treated endodontic instruments with higher flexibility values showed a reduced stress concentration map. Hyflex CM 25/04 displayed the lowest von Mises stress values of, respectively, 35.73 and 44.30 GPa for sound and mineralized dentine. The mechanical behavior of all rotary endodontic instruments was influenced by the different elastic moduli and by the dentine canal rigidity.

Highlights

The superelasticity of nickel-titanium (Ni-Ti) shape memory alloys is considered the reason for the positive mechanical behavior that allows the material to undergo high deformation without plastic residual-strain after stress removal, during transforming from the austenite to martensitic phase [1]
The NiTi is only composed of two elements: titanium and nickel, the physical and mechanical properties of NiTi alloys are significantly different from pure titanium and nickel base alloys [2]
The aim of the current research was to eval3 ofby uate the mechanical behavior of five different commercially available NiTi instruments means of a 3D-finite element analysis (FEA), focusing the influence of the material–shape combination, as well as the elastic modulus dentine root canal and 42 of means ofofa the

Summary

Introduction

The superelasticity of nickel-titanium (Ni-Ti) shape memory alloys is considered the reason for the positive mechanical behavior (consisting of a nonlinear elastic behavior) that allows the material to undergo high deformation without plastic residual-strain after stress removal, during transforming from the austenite to martensitic phase [1]. The phenomenon of NiTi endodontic instruments fracturing as a consequence of torsional overloading or cyclic fatigue is continually reported [3,4,5]. This usually happens when the tip of the instrument binds to the canal while the shaft continues to rotate [6]. Instrument durability applies an important role during the management of endodontic compromised teeth to avoid mechanical complications during dental treatment [7]

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