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

Spiros Zinelis; Georgios Polychronis; Frixos Papadopoulos; Christos Kokkinos; Anastasios Economou; Nearchos Panayi; Spyridon N Papageorgiou; Theodore Eliades

doi:10.1016/j.dental.2022.09.002

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

Dent Mater. 2022 Nov;38(11):1721-1727. doi: 10.1016/j.dental.2022.09.002. Epub 2022 Sep 16.

Authors

Spiros Zinelis¹, Georgios Polychronis¹, Frixos Papadopoulos², Christos Kokkinos², Anastasios Economou², Nearchos Panayi³, Spyridon N Papageorgiou⁴, Theodore Eliades⁵

Affiliations

¹ Department of Biomaterials, School of Dentistry, National and Kapodistrian University of Athens, Athens, Greece.
² Laboratory of Analytical Chemistry, Department of Chemistry, National and Kapodistrian University of Athens, Athens, Greece.
³ Department of Dentistry, European University Cyprus, Nicosia, Cyprus; Clinic of Orthodontics and Pediatric Dentistry, Center of Dental Medicine, University of Zurich, Zurich, Switzerland.
⁴ Clinic of Orthodontics and Pediatric Dentistry, Center of Dental Medicine, University of Zurich, Zurich, Switzerland.
⁵ Clinic of Orthodontics and Pediatric Dentistry, Center of Dental Medicine, University of Zurich, Zurich, Switzerland. Electronic address: theodore.eliades@zzm.uzh.ch.

PMID: 36123188
DOI: 10.1016/j.dental.2022.09.002

Abstract

Objectives: 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.

Methods: 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 [E_IT], Martens hardness [HM] and the elastic index [η_IT]) 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 (E_z), current density (I₃₀₀) and breaking potential (E_pit). Results were analyzed by t-test / Mann-Whitney test (α = 0.05).

Results: 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), E_IT (120.0 ± 13.2 vs 123.8 ± 12.9 GPa), or n_IT (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, E_z, and I₃₀₀). However, intraorally-aged specimens had a significantly lower breakdown potential due to degraded protection efficacy of surface oxide (P = 0.003 for E_pit).

Significance: 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.

Keywords: 3D printing; Co-Cr alloys; Corrosive resistance; Electrochemical behavior; Intraoral ageing; Orthodontic appliances.

MeSH terms

Chromium
Chromium Alloys*
Cobalt
Corrosion
Materials Testing / methods
Orthodontic Appliances*
Oxides
Printing, Three-Dimensional
Surface Properties

Substances

Chromium Alloys
Oxides
Chromium
Cobalt