Nickel Ion Release in Nickel-Containing Orthodontics Archwires: A Narrative Review of In Vitro and In Vivo Studies

Nickel-containing orthodontic archwires, particularly those made of nickel-titanium (NiTi) and stainless steel (SS), play a crucial role in orthodontic treatment using the fixed technique due to their mechanical properties. However, concerns regarding nickel-induced allergic reactions, cytotoxicity, and metal ion release, especially nickel-related ones, persist. This narrative review aims to explore recent findings on nickel release from orthodontic appliances, building upon prior systematic reviews by analyzing both in vitro and in vivo studies under various environmental conditions. The databases Web of Science, Scopus, and PubMed were searched for relevant studies that examined the relationship between nickel ion release from nickel-containing archwires and various environmental conditions. The studies found indicate that while metal ion release occurs during short-term treatment, the levels are lower than harmful thresholds, with factors such as pH, corrosion, length of treatment, and environmental influences affecting release rates. Despite this, long-term studies are few and are usually conducted only in an in vitro or in vivo environment, but not both. To establish causal relationships regarding metal ion release, in vivo monitoring of ions like Ni is critical, with further research needed to assess its prolonged effects. Furthermore, collaborative efforts among practitioners, researchers, and regulatory bodies are vital for developing evidence-based guidelines for orthodontic material selection, prioritizing patient safety and addressing metal ion release risks.