Mechanical and electrochemical characterization of 3D printed orthodontic metallic appliances after in vivo ageing

• Published in: Dental materials 2022-11, Vol.38 (11), p.1721-1727
• Main Authors: Zinelis, Spiros, Polychronis, Georgios, Papadopoulos, Frixos, Kokkinos, Christos, Economou, Anastasios, Panayi, Nearchos, Papageorgiou, Spyridon N., Eliades, Theodore
• Format: Article
• Language: English
• Subjects: 3D printing; Aging; Aging (metallurgy); Chemical composition; Chromium; Chromium Alloys; Circuits; Co-Cr alloys; Cobalt; Cobalt base alloys; Corrosion; Corrosion potential; Corrosive resistance; Electrochemical analysis; Electrochemical behavior; Electrochemistry; In vivo methods and tests; Indentation; Intraoral ageing; Materials Testing - methods; Mechanical properties; Modulus of elasticity; Open circuit voltage; Orthodontic Appliances; Orthodontics; Oxidation; Oxides; Pitting (corrosion); Printing, Three-Dimensional; Surface Properties; Three dimensional printing
• ISSN: 0109-5641; 1879-0097
• DOI: 10.1016/j.dental.2022.09.002

Three-dimensional (3D) printing technology is a promising technique for fabricating custom orthodontic metallic appliances. Aim of this study was to assess the effect of intraoral aging on the mechanical / electrochemical properties of 3D-printed orthodontic metallic appliances. Twelve molar orthodontic distalization appliances 3D-printed from cobalt chromium (Co-Cr) alloy were retrieved after intraoral use and twenty blocks fabricated under similar conditions were used as control. The samples’ microstructural / elemental composition assessment was assessed with SEM/EDS, while their mechanical properties (modulus of elasticity [EIT], Martens hardness [HM] and the elastic index [ηIT]) were measured by instrumented indentation testing. Finally, the samples’ electrochemical features were assessed with a potentiostat-connected cell arrangement in terms of open circuit potential (OCP), corrosion potential (Ez), current density (I300) and breaking potential (Epit). Results were analyzed by t-test / Mann-Whitney test (α = 0.05). The used Co-Cr alloy was found to have a highly homogenous structure with no significant differences between retrieved and new specimens in HM (4037.7 ± 215.6 vs 4090.9 ± 259.8 N/mm2), EIT (120.0 ± 13.2 vs 123.8 ± 12.9 GPa), or nIT (28.4 ± 2.6 vs 28.6 ± 2.9 %) (P > 0.05 in all instances). Metallic surfaces retained the same oxidation tendency and oxide dissolution rate in passive region in both groups (P > 0.05 for OCP, Ez, and I300). However, intraorally-aged specimens had a significantly lower breakdown potential due to degraded protection efficacy of surface oxide (P = 0.003 for Epit). The tested 3D-printed Co-Cr orthodontic appliances present clinically-acceptable mechanical properties that remained unaffected by intraoral ageing, which however degraded the protection of surface oxide against pitting corrosion. •3D-printed orthodontic Co-Cr appliances had acceptable mechanical properties.•Mechanical properties didn’t change significantly after intraoral use.•Intraoral aging didn’t affect oxidation tendency and oxide dissolution rate.•However, aging degraded the protective efficacy of oxide surface layer.