Orthodontic wires and its corrosion—The specific case of stainless steel and beta-titanium

Efficient orthodontic treatments rely on the perfect design and condition of orthodontic wires. Different wires made from different metals and alloys are available in the market. Although no wire is the best for the entire treatment, they must obey certain properties such as biocompatibility, formability, weldability, low coefficient of friction, resilience, shape memory, low stiffness, and high elastic limit. Even with the buildup of protective layers, wires exposed to the oral environment can suffer corrosion. This gradual destruction of materials resulting from chemical reactions can have several adverse effects such as the release of elements from metals, roughening of the wire surface, and weakening of appliances, which can lead to mechanical failure or even fracture of the orthodontic materials. Corrosion of orthodontic wires is strongly related with the acidic environment of the buccal cavity and the presence of fluoride ions, prophylactic agents, and mouthwash solutions. In this review, a brief description of the different commercially available wires is given. Moreover, the desirable features and properties to be considered in the search for the ideal wire are addressed. Finally, the role of pH and fluoride ions on the corrosion of wires is discussed. Results from different experiences over the years are likewise provided. Special attention is given to stainless steel and beta-titanium wires, because these two alloys are frequently used in the treatment phases in which the wires are exposed to the oral environment for lengthy periods.