Tribocorrosion behaviour of titanium in artificial saliva solutions

Abstract

Dental implants are used to replace teeth lost due to decay, trauma or periodontal disease. In last years, the demand for such implants has increased exponentially due mostly to the ageing of the population and/or increased reliability of implant therapy. To choose a material for a particular rehabilitation treatment different characteristics must be considered such as mechanical strength, elastic properties, machinability, chemical resistance, etc. There is, however, one aspect that is always of prime importance; namely how the tissue at the implant site responds to the chemical disturbance imposed by the presence of a foreign material. In this work, commercially pure titanium (grade 2) was selected mainly due to its excellent corrosion behaviour and biocompatibility, that make this material one of the most used in dentistry. The tribocorrosion behaviour of the material in conditions simulating mastication, when in contact with artificial saliva solutions was investigated. Corundum was used as counterface material. The tests were performed, at MTM- KULeuven (Belgium), in a fretting machine specially adapted for tribocorrosion experiments. A normal load of 2 N was applied to the specimens and a displacement amplitude of 200µm at a frequency of 1 Hz. The number of cycles was varied between 5.000 and 10.000. In order to simulate different environmental conditions, simple artificial saliva (0.7%KCl + 1,2%NaCl; pH =6), artificial saliva with corrosion catalyst (citric acid), and artificial saliva with anodic, cathodic and organic corrosion inhibitors (sodium nitrite, calcium carbonate or benzotriazole, respectively), was used. The tribocorrosion degradation mechanisms were investigated by Electrochemical Noise technique (TEN), which combines Electrochemical Emission Spectroscopy with fretting tests [1]. After being tested, the surface of the samples was investigated by SEM and EDX. Roughness measurements and wear volume measurements were also performed. The depassivation/repassivation phenomena occurring during the tests were clearly detected, and are discussed. Considering the influence of the corrosion inhibitors, it was possible to observe that the degree of protection varies with the nature of the inhibitor.