Semiconductive properties of passivated titanium and titanium based hard coatings on metals for implants--an experimental approach.

Titanium is used in the field of dental implants on account of the fact that they are integrated into body tissue virtually reaction-free. This integration is made possible by the passivated layers which form within the body electrolyte, and which can be described in the terms of a semiconductive solid body. A prerequisite, however, is the prevention of relative movement between the implant and the tissue so that the passivated layer is not destroyed. The low resistance to shearing, and the oxide stoichiometry--which under in vivo conditions cannot be influenced--on repassivation following mechanical destruction strongly suggest that, during fabrication, implants should be provided with wear-resistant coatings having defined solid state properties which are similar to those of electrochemically passivated titanium surfaces. In the clinical test are already employed, a (Ti,Nb)ON- and a (Ti,Zr)O-coating on titanium and TiAl5Fe2.5. One of the most important parameters for the solid body-physical description of semiconductive hard coatings is the energy gap between conduction and valence band of the electronic structure, which are determinative for the physical-chemical behaviour of the implant surface within the body. The contribution describes the experimental procedure and the results of determinations of the energy gap at singularities in the Brillouin zone for titanium, the titanium alloys in clinical use, and some hard coatings in clinical test. The experimental method of choice for surfaces in contact with aqueous electrolytes is the electroreflectance spectroscopy.