Micro- and nano-scale topographical alterations in dental alloys after exposure to artificial saliva: a combined...

This study aimed to evaluate the surface topography and chemical stability of six commonly used orthodontic archwires: nickel-titanium, gold- and rhodium-coated nickel-titanium, stainless steel, nickel-free stainless steel, cobalt-chromium-nickel, and beta-titanium under simulated intraoral conditions. Two widely applied analytical methods were used: atomic force microscopy (AFM) and scanning electron microscopy with energy-dispersive X-ray spectroscopy, complemented by additional post-processing of the obtained data. Archwires were analyzed in their untreated state and after 28 days of exposure to artificial saliva at two pH values (5.5 and 6.6). Nickel-titanium archwires showed moderate roughness and a stable nickel : titanium ratio, but were not the most resistant under all of the conditions. Coated nickel-titanium archwires showed smoother surfaces and lower element losses, indicating a protective effect of the coating. Stainless steel wires showed moderate corrosion and localized surface cracking at pH 5.5, while Ni-free stainless-steel wires were most affected by acidic conditions and exhibited pronounced degradation and high oxygen content. Cobalt-chromium-nickel archwires maintained their surface integrity better at pH 6.6, but showed selective dissolution at pH 5.5. Beta-titanium archwires exhibited localized oxidation but stable elemental composition, supporting their potential as a hypoallergenic alternative. The inclusion of three-dimensional AFM parameters allows a more comprehensive and nuanced assessment of surface morphology, capturing subtle changes that may not be apparent with conventional two-dimensional roughness analysis alone. These results emphasize the importance of material selection based on corrosion resistance and surface stability, especially for patients with acidic oral environments or metal sensitivities.