Electrochemical behaviour of pure titanium in alternative linear regime of sliding in contact with artificial saliva solutions

Dental implants are used to replace teeth lost due to decay, trauma or periodontal disease. During mastication, dental implants are simultaneously subjected to corrosion by the oral environment and to the sliding-wear process by bite forces. Tribo-electrochemical techniques can be used to investigate in situ the combined corrosion-wear degradation of materials in sliding contacts immersed in electrically conductive solutions. Thus, the main goal of the present work was to study the corrosion behaviour of commercially pure titanium in different artificial saliva solutions during a reciprocating sliding test. This project represents an effort towards the understanding of the deterioration process occurring in dental implants during mastication. The material selected was pure titanium grade 2, which is used in practice to produce dental implants due to its excellent corrosion behaviour and biocompatibility. To simulate the oral environment, different kinds of saliva including pure artificial saliva with a simple composition (NaCl + KCl), as well as, artificial saliva with addition of different additives (citric acid, anodic, cathodic and organic inhibitors) were used. The pH of the solutions was varied between 5 and 7. The surface roughness and topography of the titanium samples were evaluated prior to testing. A reciprocating sliding test was performed to simulate the process of mastication, and to investigate the behaviour of the material under such circumstances. Long duration tests were performed (11160 cycles), with an amplitude of 6mm, an applied load of 10N, and a frequency of 1Hz. As shown in figure 1, during the experiments the open circuit potential (OCP) of the samples was continuously monitored. Also, electrochemical impedance spectroscopy (EIS) measurements were performed after a stabilization period, before starting the wear test, and again after repassivation. Electrochemical results (OCP and EIS) were useful for following the evolution of the characteristics of the passive film through the tests. Although, presenting a lower tendency for corrosion, a higher weight loss was measured in samples tested in artificial saliva solutions with addition of citric acid. Additionally, cathodic and organic inhibitors solutions revealed a higher tendency for corrosion, forming an oxide passive film with lower protection characteristics. 0.05.0x1031.0x1041.5x1042.0x1042.5x104-1.1-1.0-0.9-0.8-0.7-0.6-0.5-0.4-0.3-0.2-0.10.0E ( V.vs.SCE)Time (s)As As Citric acidAs with anodic inhibitorAs with cathodic inhibitorAs with organic inhibitorEnd of slidingBeginning of slidingFigure 1: Evolution of the open circuit potential with time for titanium grade 2 against corundum in saliva artificial solution (As) and As with citric acid, anodic, cathodic and organic inhibitor