Nano Topography Evaluation of NiTi Alloy Exposed to Artificial Saliva and Different Mouthwashes ^†

Abstract

Evaluation of NiTi alloy corrosion behavior in conditions that exist in the oral cavity still remains a great characterization challenge. Such characterization is commonly simplified by avoiding the use of non-accelerated corrosion tests. Accordingly, difficulties in the characterization of material changes on a nano level are avoided, and results do not sufficiently resemble the real situation. Therefore, the motivation of this work was to perform a non-accelerated corrosion test to characterize the nano-topographic changes, and to evaluate the obtained results by statistical methods. In this study, we examined the behavior of NiTi alloy (50% Ni, 50% Ti) archwires exposed for 21 days to different corrosive mediums: artificial saliva, Eludril^®, Aquafresh^® and Listerine^®. The corrosion was characterized by means of changes in surface topography. This was conducted by contact mode atomic force microscopy on all samples at five locations of 10 µm × 10 µm areas before and after the corrosion tests. Image analysis software was used for the analysis of topographic images and the calculation of surface roughness parameters Sa and S10z. The changes to the roughness parameters were statistically analyzed by ANOVA. Sa and S10z parameters displayed changes with a trend for all treatments. However, the confidence interval for all cases was overlapped. Statistically analyzed data revealed that all samples exposed to mouthwashes displayed significant changes in parameter S10z, while only samples exposed to Aquafresh^® and Eludril^® displayed significant changes in parameter Sa. On the other side, samples exposed to artificial saliva did not display significant changes in any parameter. As such, it is implied that mouthwashes have a significantly higher effect on surface topography. Differences in the confidence interval of the Sa parameter indicate that changes in roughness parameters caused by corrosion do not depend on the initial surface roughness. In this study, statistical analysis methods have been proven as a useful tool in the characterization of nano-topographic changes caused by corrosion in real conditions.