Semi-conducting properties of titanium dioxide surfaces on titanium implants.

The properties of the TiO2 layer on titanium implant surfaces are decisive for good contact with the surrounding tissue. The oxide properties can be deliberately changed by for example chemical etching, ion incorporation or anodisation. In the present study impedance spectroscopy was used to study the semi-conducting properties of the naturally formed oxide for different pre-treatment of the surface. A turned surface was used as a reference and both physical (blasting) and chemical (hydrofluoric acid etching) treatments were investigated. Blasting of a titanium sample introduces defects in the metal surface and the study clearly shows that also the oxide layer contains defects leading to a higher number of charge carriers (increased conductivity) compared with the oxide on the turned surface. The hydrofluoric acid etching of the blasted surface results in an oxide film with even higher conductivity. Indication of the defect oxide structure for fluoride treated samples was also seen when analysing the TiO+/Ti+ ratio from ToF-SIMS data. The lowest value of this ratio was obtained for the HF etched sample, indicating a less stoichiometric oxide compared to the other surfaces. This is a result of incorporation of fluoride ions in the oxide, as proven by adsorption studies on a TiO2 suspension. The results were treated in the context of surface complexation and two surface complexes were identified. Our results are discussed in relation to pull-out data on rabbit. The pull-out forces depend primarily on surface roughness but the contribution from the hydrofluoric acid etching might be explained by fluoride ion incorporation and the resulting increase in oxide conductivity.