Multi-Element Ion Release from Stainless Steel and Nickel–Titanium Orthodontic Archwires in Neutral and Fluoride-Containing Artificial Saliva: A Factorial In Vitro ICP-OES Study

Background: Corrosion of orthodontic archwires raises biocompatibility concerns; yet, comparative multi-element data across manufacturers remain scarce. Methods: Ni, Cr, Fe, and Ti release was quantified by ICP-OES from SS and NiTi rectangular archwires (0.43 × 0.64 mm) from four manufacturers (Ormco, 3M Unitek, Dentaurum, and American Orthodontics) and immersed in artificial saliva (pH~7.0) and fluoride-containing saliva (+0.05% NaF) at six time points (days 1–35). Release was normalised to wire mass (mg g−1). Non-parametric tests were applied. Results: NiTi wires released significantly more Ni than SS wires in +NaF at all time points (p = 0.029). An exploratory manufacturer effect on Ni release from NiTi was detected (Kruskal–Wallis H = 12.99, p = 0.005); American Orthodontics exceeded Dentaurum and Ormco. Ormco SS released ~3-fold more Fe than other SS wires (H = 13.68, p = 0.003). Ti was detectable exclusively in NiTi wires in +NaF; all specimens were below LOQ in pH~7.0. Cr release was uniformly low (0.017–0.023 mg g−1). Conclusions: Manufacturer identity influences Ni and Fe release independently of alloy type. Fluoride selectively disrupts the NiTi passive film. These exploratory findings, derived from a single-specimen pilot design, may inform clinical material selection in nickel-sensitive patients pending replication.