Combined bending–torsion testing device for characterization of shape memory alloy endodontic files

Abstract

Design has an important influence on mechanical response of endodontic instruments made of shape memory alloys. The experimental and numerical prediction of their thermomechanical response is necessary to improve their behavior during operating inside root canal. Due to the curved and tapered shape of the dental canal, endodontic files are subjected to rotating bending during the root canal preparation phase. These rotative bending could ever be combined with torsion when the instruments are engined in the root canal. Bending and torsion tests available in the standard ISO 3630-1 do not take into account this combined loading leading to a response different from the one obtained by superposition of separated bending and torsion loadings. This article details the design and the realization of bending–torsion testing device particularly adapted to shape memory alloy endodontic files. It allows to control the torsion and the bending rotations in a separate or a combined way. Qualification tests using this bending–torsion testing device on NiTi wires showed a good agreement between the experimental and the simulated responses. Finally, this bending–torsion testing device allowed to analyze the response of various NiTi endodontic files, currently used in endodontics, subjected to bending, torsion, and combined bending–torsion loadings. Obtained results showed clearly that combined bending–torsion loading changes significantly the shape memory alloy file response.

Experimental Analysis of the Influence of Heat Treatments on the Flexibility of NiTi Alloy for Endodontic Instruments Manufacturing

“…To evaluate the bending properties of endodontic instruments, the ISO 3630-1 established a bending test, which involves clamping 3 mm of the tip of each instrument into a chuck and applying an angular deflection of 45 • [5,45]. In this study, the bending test for NiTi samples was performed according to this standard by using a new bending-torsion testing device [46]. The curves obtained from the bending test (Figure 4a, b) show bending loads at specific angles of rotation, corresponding to two different ranges: the elastic and the superelastic ranges, respectively.…”

“…This sub-system has a rotation axis perpendicular and coplanar to the sample axis. The third sub-system is the frame of the device on which the bending sensor and actuator are positioned [46]. This device allows for controlling the torsion and the bending rotations in a separate or a combined way.…”

“…The bending test was carried out at room temperature (20 • C) using a testing machine developed by Xolin et al [46]. It allows us to apply a bending and/or torsion rotation to a sample or a wire clamped in the two extremities leaving the axial displacement free.…”

“…Flexibility will be evaluated by measurement of torque for a given maximum rotation, through a bending test under ISO 3630-1 standard [45]. Contrary to previous studies, the bending test will be carried out at fixed number of cycles by using an adapted designed bending and torsion bench [46].…”

Transient swelling of cylindrical hydrogels under coupled extension-torsion: Analytical and 3D FEM solutions

“…There are several standard deformation regimes used for material characterization (Pashazadeh et al, 2021; Xolin et al, 2020), and one of the most important is coupled extension and torsion. This is due to the fact that this deformation regime involves both the tensile and shear modes of deformation simultaneously.…”