Mechanical and Metallurgical Characterization of Nickel-Titanium Wire Types for Rotary Endodontic Instrument Manufacture

Abstract

This study aimed to evaluate and compare the effects of ambient temperature and post-manufacture heat-treatment on the mechanical behavior of nickel-titanium (NiTi) wires. Four types of commercial NiTi variants (Stock NiTi, heat treated “Blue”, “Gold”, “Superflex”, all Dentsply Maillefer, Ballaigues, Switzerland) were stressed in a tensile testing machine in a temperature-controlled water bath at three different temperatures. Stress and strain values were extrapolated from the raw data, and 2-way ANOVA and Tukey’s test for multiple comparisons were performed to compare the differences of the mechanical constants. Differential scanning calorimetry (DSC) tests established the martensitic transformation starting (Ms), finishing (Mf) and austenitic (reverse-martensitic) starting (As) and finishing (Af) points. Austenitic modulus of elasticity and transformation stress values increased with temperature for all NiTi groups. The martensitic modulus of elasticity, maximum transformation strain and ultimate tensile stress were not significantly affected by temperature changes. Stock NiTi and Gold wire samples presented with clearly delineated austenitic and martensitic transformations in the DSC experiments. Differences in manufacturing/heat treatment conditions and ambient temperature affect the mechanical behavior of nickel-titanium and may have clinical implications. Further improvements to the experimental setup could be considered to provide more accurate measurements of strain.

The extended finite element method in endodontics: A scoping review and future directions for cyclic fatigue testing of nickel–titanium instruments

“…On the other hand, NiTi alloys exhibit excellent ductility (Yahia et al, 2009 ) and thus XFEM alone may not be suitable for modelling cracks in ductile materials, given that a significant plastic region occurs before tensile failure (Kumar & Bhardwaj, 2018 ). To complicate matters, NiTi alloys do not exhibit linear elastic deformation, due to the formations of intermediate transformation states such as the rhombohedrally distorted phase (R‐phase) when load is applied (Chien et al, 2022 ). Previous work has demonstrated that these regions of plastic deformation are seen before fracture (Chien et al, 2022 ).…”

“…To complicate matters, NiTi alloys do not exhibit linear elastic deformation, due to the formations of intermediate transformation states such as the rhombohedrally distorted phase (R‐phase) when load is applied (Chien et al, 2022 ). Previous work has demonstrated that these regions of plastic deformation are seen before fracture (Chien et al, 2022 ).…”

“…Many NiTi endodontic instruments in the current market have undergone various thermomechanical treatments to enhance their performance during the chemomechanical preparation of root canals. Postmanufacture processing of NiTi alloys such as Blue and Gold treatment may not necessarily alter the core composition of NiTi, but it can alter the thresholds for martensitic and austenitic transformations (Chien et al, 2022 ). Given that there exist over 160 proprietary endodontic instruments in the global market (Gavini et al, 2018 ), it may be difficult to model accurately each instrument without access to all of their individual mechanical parameters.…”

Strain Rate Effect on the Thermomechanical Behavior of NiTi Shape Memory Alloys: A Literature Review

“…Examples include: (1) The dissipation heat by martensitic transformation as considered by Boyd and Lagoudas [94] in the Gibbs free energy (11) with the corresponding term π ξ . ξ in the temperature evolution equation (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16). (2) The dissipation heat by the martensite reorientation was taken into account by Šittner et al [60] in the Gibbs free energy with a function of the volume fraction of each martensite variant.…”

“…NiTi Shape Memory Alloys (SMAs) are the most widely used in the shape memory material family, and have important applications in electronic components, medical devices, shock absorption devices, etc., thanks to their unique thermomechanical behaviors [1][2][3][4]. Reliable and predictive simulations of NiTi SMA wires under high strain rates are always required for actuation and auxiliary control.…”