Influence of the treatment period on the morphology and the chemical composition of the thermally activated orthodontic archwires

The thermally activated nickel-titanium archwires are widely employed in orthodontics because they present shape memory effect and super elasticity. The addition of copper to nickel-titanium alloy enhances the thermal properties of the wire while maintaining precise control of forces, comparing to "pure" nickel-titanium alloy. The purpose of this study is to investigate the chemical composition of the surface of thermally activated copper-nikel-titanium archwires with different cross sections (round -0.33 mm and rectangular -0.41 x 0.56 mm). For the purpose of comparison, the origin wires (unused and sterilized ones) are also investigated as a control group. All studied orthodontic wires have transition temperature range at 35 degrees C. The analyses are carried out by three independent methods as X-ray diffraction analysis (XRD), Scanning Electronic Microscope (SEM) and by an Energy Dispersive X-Ray method (EDX). The obtained results show that the processes of sterilizations of the investigated orthodontic archwires have no adverse effects on their properties. From the carried out tests it is established that there are no significant changes in the chemical composition of the surface of the thermally activated wires after treatment period up to 6 and after 8 weeks. This period covers the average time of residence of the orthodontic wires in the mouth of the patient.