Assessment of the surface roughness and susceptibility to corrosive processes of titanium-niobium and titanium-molybdenum archwires in laboratory tests

Introduction
The development of production technology and the willingness to create medical materials with the most beneficial clinical properties result in new generations of products being introduced to the market or those already in use being modified. Laboratory tests can help determine the properties of materials suitable for use under clinical conditions and help when deciding on the optimal treatment for a given approach.

Aim
The aim of the study was to assess the susceptibility to corrosion and surface roughness of two types of orthodontic archwires made of titanium alloys.

Material and methods
The study evaluated orthodontic archwires with the cross-section of 0.017 by 0.025 inch (0.04 by 0.06 cm) by RMO (USA) and Morita (Japan), made of titaniumniobium and titanium-molybdenum alloys, respectively. Surface topography of tested specimens was evaluated using the scanning microscope, whereas corrosion resistance was assessed by a potentiodynamic technique. The roughness of materials was also evaluated using an optical profilometre. The obtained results were subject to statistical analysis at the significance level of p = 0.05.

Results
The analysis of numerical data obtained from potentiodynamic studies shows that the average corrosion current intensity (Icor) was higher for RMO materials, compared to Morita materials, namely 0.0033 μA/cm2 and 0.0029 μA/cm2, respectively. The values described were not statistically significantly different (p = 0.036).

Conclusions
1) Orthodontic archwires evaluated in the study were subject to corrosion, regardless of the material manufacturer and elemental composition. 2) Significant differences observed in the surface roughness of both orthodontic archwires evaluated in the study may indirectly indicate their different potentials to generate frictional forces under clinical conditions.