In vitro assessment of polishing efficiency for additive-manufactured Co–Cr alloy clasps

Purpose: The processes and methods of treating and polishing additive-manufactured (AMed) cobalt-chromium (Co–Cr) alloy clasps were assessed in vitro to determine their suitability for constant clinical use and the reduction of dental technician work.

Methods: AMed Aker clasps were fabricated by selective laser sintering of approximately 50 μm Co–Cr alloy powders. After the nodules and fins on the inner surface of the AMed clasps were removed and morphological correction was performed, a dental technician manually polished the clasps as a control. Four surface treatments, barrel finishing, shot peening, and wet and dry electropolishing, were performed to obtain smooth surfaces. In addition, hybrid manufacturing, which integrates repeated laser sintering and high-speed milling for one-process molding, was added to this study. After observing the treated surfaces using SEM and Hybrid Laser Microscope (HLM) the surface roughness, fitness accuracy, and retentive forces of the treated AMed clasps were measured, and their polishing efficiencies were compared.

Results: Similar to manual polishing, dry electropolishing yielded the smoothest surfaces in all treatments. The fitness accuracy of all clasp regions and treatment methods ranged from 80 to 140 μm, without significant differences among the treatment methods. All treated clasps showed acceptable retentive forces for clinical use, and hybrid manufacturing and wet electropolishing showed significantly higher forces.

Conclusions: AMed Co–Cr clasps with all surface treatments could be clinically used if additional slight manual polishing was performed; however, each processing condition should be carefully selected.