Influence of fluorine-containing mouthwashes on NiTi Alloy corrosion

Abstract

Evaluation of NiTi alloy corrosion behaviour in fluorine-containing media still remains a great characterization challenge. Such characterization is commonly simplified by using aggressive media with a high concentration of fluorine. Accordingly, the difficulties in the characterization of material changes on a nano-level are avoided. However, these results do not sufficiently resemble the real situation. Therefore, the motivation of this work was to perform a non-accelerated corrosion test, characterize the nano topographic changes, and to evaluate the obtained results by statistical methods. In this study, we examined the behaviour of NiTi alloy archwires exposed for 21 days to artificial saliva and fluorine-containing mouthwash Aquafresh My Big teeth®. Atomic force microscope (AFM) Veeco CP-II, and scanning electron microscope (SEM) Hitachi TM3030, were employed for characterization of changes in surface topography, on the areas of 80x80 and 10x10 μm. Before and after the corrosion tests specimens were evaluated at 5 locations of 80x80 μm. Topographic images were analysed by image analysis software (Spip 6.2.0) and surface roughness parameters (Sa and S10z) were calculated. The changes in chemical composition were evaluated by energy-dispersive X-ray spectroscopy (EDS). Paired T-test and one-way ANOVA statistical analysis were employed for the evaluation of the changes observed in surface roughness parameters and chemical composition. Changes in surface topography observed in AFM and SEM images (80x80 μm) are negligible for both specimens. Analysis of AFM topographic images (10x10 μm) revealed that only specimen exposed to Aquafresh My Big teeth® exhibited nano changes in surface topography. For artificial saliva negligible changes were observed, while Aquafresh My Big teeth® exhibited notable changes in Sa and S10z parameters. Statistical analysis of data revealed that changes in roughness parameters are significant only for specimens exposed to Aquafresh My Big teeth® ®. This indicates that the presence of fluorine in mouthwash increases the NiTi corrosion. Statistical analysis methods and AFM have been proven as a valuable tool in the characterization of nano topographic changes caused by corrosion in real conditions.