On the fatigue resistance of endodontic files subjected to electrochemical polishing and an autoclave’s sterilisation cycle

Abstract

Purpose The purpose of this paper is to improve the surface finish and, therefore, the fatigue resistance of some endodontic files by electrochemical polishing; the influence of applying an autoclave’s sterilising cycle to the endodontic files under study was also assessed during the research herein presented. Design/methodology/approach In total, 22 Ni-Ti endodontic instruments of two sizes, namely, ref. Hyflex 0.04/20 and 0.06/20 (taper: 0.04; 0.06 and tip diameter: 0.20 mm, respectively), were submitted to rotational bending tests at 500 rpm; the radius and the angle of curvature imposed to the endodontic instruments during the experimental tests were equal to 4.7 mm and 45°, respectively. In addition, 18 endodontic files (out of the 22) were subjected to electrochemical polishing before in vitro fatigue tests had been carried out. Several combinations of electrochemical parameters were considered during the preliminary experiments involving electrolyte, voltage, flow rate and duration. The endodontic files under study were weighted using a high-precision balance before and after polishing, and mass variation was determined. Also, a sterilising cycle was applied to six polished endodontic instruments, which were placed inside an autoclave at 134°C, for 30 min, and under a pressure of 2.16 bar. Findings The fatigue resistance of as-received endodontic files ref. 0.04/20 is much larger (+480 per cent) than the fatigue strength of endodontic files ref. 0.06/20. The weight variation due to electropolishing was comprehended between 0.53 mg and 1.01 mg, and the fatigue resistance of all polished endodontic instruments increased between 30 per cent (0.06/20) and 80 per cent (0.04/20) when compared with the fatigue resistance of the as-received files. The application of an autoclave’s sterilisation cycle had a negative impact on the fatigue resistance of instruments ref. 0.04/20 and a positive impact on the durability of instruments ref. 0.06/20. Originality/value The application of an electrochemical polishing process increased the fatigue resistance of the endodontic files under study significantly, and the values for the variables of the electrochemical process were never published elsewhere. The surface finish improvement was obtained by immersing the endodontic files in a Struers’ Electrolyte (ref. E2) for 3 s while applying 30 volts and a flow rate of 1.