Nickel Ion Release from Orthodontic Archwires: A Narrative Review of In Vitro and In Vivo Evidence

Nickel-based orthodontic archwires, particularly nickel-titanium (NiTi) and stainless steel (SS), remain essential in fixed orthodontic therapy because of their favorable mechanical behavior. Nevertheless, concerns persist regarding nickel-associated hypersensitivity, cytotoxic effects, and ion release. This review examines recent evidence on nickel release from orthodontic devices, expanding upon earlier systematic reviews by incorporating both in vitro and in vivo investigations conducted under various conditions. Literature searches were performed in Web of Science, PubMed, and Scopus to identify studies that assessed the relationship between environmental factors and nickel ion release from archwires containing nickel. Current findings indicate that ion release occurs mainly during the early treatment phase but remains well below toxic thresholds. Influencing factors include pH variation, corrosion processes, treatment duration, and oral environmental conditions. However, most studies have been short-term and confined to either in vitro or in vivo settings, rarely combining both. To establish stronger causal evidence, continuous in vivo monitoring of nickel release is required, alongside further studies into long-term health implications. Collaborative efforts involving clinicians, researchers, and regulatory organizations are necessary to establish evidence-based recommendations for orthodontic material selection, focusing on minimizing nickel exposure and prioritizing patient safety.