Ionic release and electrochemical testing of 3-D printed orthodontics metallic bands made of Co-Cr and stainless-steel alloys

Objective The aim of this study was to investigate the electrochemical characteristics and ionic release of three-dimensional (3D) printed orthodontic metallic bands made of stainless-steel (SS) and Cobalt-Chromium (Co-Cr) alloys. Materials and Methods Thirty-six orthodontic metallic bands were prepared by 3D printing, employing SS (n = 18) and Co-Cr (n = 18) alloys. The ionic release from each alloy was determined according to ISO 27020:2019 requirements employing flame atomic absorption spectrometry (FAAS). The electrochemical properties were characterized by Open Circuit Potential (OCP), Anodic Scan (AS) and Electrochemical Impedance Spectroscopy (EIS). In all cases a 0.1M NaCl, 0.1 M lactic acid solution was used. The EIS data were fitted to a Randles circuit and the sum of ionic release of probed elements after immersion along with OCP, zero corrosion potential (Ecorr), corrosion current density (Icorr), and pitting corrosion potential (Epit) were compared with t-tests/Mann-Whitney tests (α = 0.05). Results SS bands showed an approximately 44-fold higher total ionic release compared to Co-Cr ones. Electrochemical testing revealed no statistically significant differences for Ecorr but Co-Cr illustrated more beneficial OCP, Icorr and Epit values than SS. Both alloys illustrated semicircles in Nyquist plots, implying that the electrochemical process was under charge transfer control, while the equivalent circuit simulation showed a higher charge transfer resistance for Co-Cr alloy (SS:14191.1 vs Co-Cr:33158.7 Ωcm2), implying lower corrosion current and thus decreased corrosion rate. Conclusion Immersion and electrochemical testing indicated that Co-Cr alloys showed increased corrosion resistance over SS ones, which might affect efficacy under clinical use.