Nickel-titanium (NiTi) and stainless steel (SS) archwires are fundamental components of fixed orthodontic therapy due to their unique mechanical properties. Despite their widespread use, there is ongoing concern regarding nickel-related adverse effects, including hypersensitivity reactions, cytotoxicity, and the release of metal ions into the oral environment. This narrative review synthesizes recent research on nickel ion liberation from orthodontic archwires, incorporating both in vitro and in vivo studies under varying environmental conditions, building on insights from prior systematic reviews. Searches of Web of Science, Scopus, and PubMed were conducted to identify studies examining how factors such as pH, corrosion, duration of use, and other environmental variables influence nickel release. Evidence indicates that while nickel ions are detectable during short-term exposure, the concentrations generally remain below thresholds associated with toxicity. Long-term data, however, are sparse and often limited to either laboratory or clinical settings rather than both. Comprehensive in vivo monitoring is essential to clarify the clinical relevance of nickel release and its potential systemic impact over time. Coordinated efforts among clinicians, researchers, and regulatory agencies are necessary to inform material selection, minimize patient risk, and establish evidence-based guidelines for the safe use of nickel-containing orthodontic appliances.
