Abstract
To evaluate the properties of two nickel–titanium (NiTi) reciprocating endodontic instruments (commercially known as Procodile and Reziflow), a total of 40 size 25 and 0.06 taper new Procodile and Reziflow instruments (n = 20) were subjected to cyclic fatigue tests (60° angle of curvature, 5-mm radius) at 20 °C and 37 °C and a torsional test based on ISO 3630-1. The fracture surface of each fragment was examined. The morphological, mechanical, chemical, thermal, and phase composition characteristics of the files were investigated by field-emission gun scanning electron microscopy (FEG-SEM) equipped with an energy-dispersive X-ray (EDX) detector, focused ion beam analysis (FIB), micro-Raman spectroscopy, X-ray diffraction (XRD), differential scanning calorimetry (DSC), and Auger electron spectroscopy (AES). Reziflow showed higher cyclic fatigue resistance than Procodile at 37 °C (p < 0.05). The maximum torsional strength of Procodile was lower than that of Reziflow (p < 0.05). No difference was found between their angular rotations to fracture (p > 0.05). SEM, FIB, Micro-Raman, and AES analyses revealed the presence of an Nb/Nb2O5 coating on the Procodile surface. DSC and XRD analysis confirmed that both files consist of an almost austenitic phase structure at 37 °C. The cyclic fatigue resistance of Procodile and Reziflow significantly decreases upon exposure to body temperature.
Highlights
Nickel–titanium (NiTi) endodontic instruments, called files, have numerous advantages, such as greater flexibility and the capacity to follow the root canals without making ledges or perforations [1,2]
One instrument for each type was selected for micro-Raman spectroscopy and two Procodile files were selected for Auger electron spectroscopy with depth profiling
Cyclic fatigue testing of all instruments at 37 ◦ C significantly reduced their time to fracture (TtF) compared with the ones fractured at 20 ◦ C (p < 0.05), Table 1
Summary
Nickel–titanium (NiTi) endodontic instruments, called files, have numerous advantages, such as greater flexibility and the capacity to follow the root canals without making ledges or perforations [1,2]. Failure may occur under torsional loading, if the file gets locked inside the root canal while the shank still rotates [6], or when the friction between the instrument and canal wall results in a torque above the elastic limit of the alloy In the latter case, the file shows plastic deformation followed by fracture [4]. The reciprocating motion consists of an alternating oscillation of the file in both directions, and it may increase the cyclic fatigue resistance of the file [11] compared to the continuously rotated one This type of motion reduces the risk of fracture, as well as the operating time, even for inexperienced operators [4,12]. The null hypothesis is that there is no difference between the mechanical properties and the metallurgical features of the tested files
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