Abstract
In the present work, stainless steel and Ni-Ti commercial orthodontic wires were immersed in artificial saliva solutions, containing or not F- ions, in different pH values, during 30 days. The weight loss and the Ni2+ content in the solutions at 15 and 30 days of exposition were evaluated using a composite design 23 and response surface methodology. The open circuit potential (OCP) was measured over the same period of time. Polarization curves and morpHological analysis of the wires before and after the corrosion experiments were also carried out. The results showed that corrosion of the studied metal alloys depended on a combination among saliva pH, the exposition time, and the concentration of F- ions in the solution. The critical condition was observed for Ni-Ti wires at pH = 3.0, and high concentration of F- ions, causing a decrease in the OCP values and an increase in Ni dissolution and corrosion current density.
Highlights
Titanium alloys such as TMA (Ti-Mo-Sn-Zr), Ti-Nb, Ni‐Ti and Cu-Ni-Ti are generally used as biomaterials, mainly as orthodontic wires, because of their interesting elasticity and shape memory capacity, which allow these materials to return to their original configurations after being submitted to a stress[1,2,3,4,5]
Morphology of the as-received commercial wires. Both stainless steel (SS) and Ni-Ti wires were acquired from the same manufacturer, since we aimed to evaluate statistically the effects of the chosen parameters on these wires, only
There was no intention in comparing their performance with other kind of wires used in orthodontic treatment or with the same wires produced by other manufactures
Summary
Titanium alloys such as TMA (Ti-Mo-Sn-Zr), Ti-Nb, Ni‐Ti and Cu-Ni-Ti are generally used as biomaterials, mainly as orthodontic wires, because of their interesting elasticity and shape memory capacity, which allow these materials to return to their original configurations after being submitted to a stress[1,2,3,4,5] These properties, that are not observed in the traditionally used stainless steel wires (generally called Cr-Ni wires by the dentists), permit the orthodontist to apply continuous forces on the teeth, without causing discomfort to the patient. Ni-Ti-based alloys present a large Ni content (about 48-55% mass), and a negative aspect that hinders their wide use in prolonged orthodontic treatment takes into account the Ni corrosion in oral cavity This point is a constant concern of many Dentistry professionals, since the presence of the ion Ni2+ in the oral medium can cause several allergies to the patients[1,6]. It implies that corrosion resistance must be another important item to be estimated for the prolonged using of these materials in orthodontic treatments
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