Corrosion of laser-welded stainless steel orthodontic wires

Purpose: Fabricating orthodontic appliances using laser welding has the clinical advantage of biocompatibility, because the welded joint does not require soldered alloy. The purpose of this study was to investigate the corrosion of laser-welded stainless steel wires in acidic environments. Materials and methods: Laser welding of stainless steel wires with a 0.021 × 0.025 in cross-section was performed at an energy output ranging from 0.5 to 1.3 kW. A control sample was prepared using conventional soldering. The samples were immersed in 1% lactic acid aqueous solution for 7 days. After immersion, the concentrations of metallic ions in solution were measured using inductively coupled plasma atomic emission spectroscopy. Tensile loading tests were carried out with and without lactic acid immersion. Scanning electron microscopy was used to examine the microstructure of laser-welded samples. Results: The concentrations of metallic ions detected in solution for laser-welded samples were significantly lower than that for soldered sample. There was no significant difference among the mean tensile strengths with and without immersion for laser-welded samples. The penetration depth and the localized region fused by laser irradiation increased with energy output, and ductile fractures were observed in the fused region of laser-welded samples. Conclusion: Laser welding of stainless steel orthodontic wires should be acceptable for clinical use, because the joints showed sufficient strength and the original structure was not significantly altered. Immersion in acidic solution had minimal effect on the mechanical performance at the joint regions, and showed minimal acceleration of metallic ion release.