Surface Modification Of The Dental Zirconia Implants

Zirconia ceramics have attracted considerable attention from the scientific and medical communities since that introduced in 1960s due to their excellent biocompatibility, good mechanical properties and aesthetic qualities. However, some characteristics of zirconia ceramics limited its development. First of all, one of the main problems concerning zirconia ceramicsis their sensitivity to low temperature degradation (LTD), and ageing often occurs by a slow surface phase transformation from the tetragonal zirconia to the stable monoclinic phase in the presence of water or water vapor. LTD results in not only undesirable transformation, but also surface roughening, microcracks, grain pull-out, and loss of strength. Surface roughening and microcracks may degrade wear resistance and induce delayed fracturing.On the other hand, zirconia ceramics are considered to be bioinert, and do not naturally form a bond with bones. After implantation, intervening fibrous tissue develops around the implant, which can lead to premature failure of the implant. Currently, many studies are investigating methods for modifying the surface properties of zirconia with the aim to achieve zirconia ceramics with long useful life and high biological activity, which make zirconia ceramics enough to use in biological materials.In this work, titanium dioxide (TiO2) coating, Si-doped octacalcium phosphate coating and bioglass coating were prepared to prevent the low temperature degradation and improve the bioactivity of zirconia ceramic implants.Titanium dioxide (TiO2) coating was prepared by sol-gel method on the zirconia substrate for preventing the LTD behavior. he acceleration ageing test shows that the ratio of the monoclinic phase transition decreased from 10% for the originalzirconia substrate to 4% for the TiO2-coated substrate. And then, Si-doped octacalcium phosphatecoating was prepared by biomimetic mineralization and bioglass coating were prepared by blade coating. The surface microstructure and morphology of the coatings were examined using a scanning electron microscope with an energy-dispersive microanalysis system. The microstructures of coatings were analyzed by X-ray diffraction spectroscopy and Fourier transforms infra-red spectroscopy. As to the Si-doped octacalcium phosphate coating prepared by biomimetic method, the main phase composition of the coating was octacalcium phosphate. The morphology of the coating was lamellar-like, and the surface was uniform and continuous with no cracks being observed. It is suggested that Si was added into the coating both through substituting for PO43- and doping as NaSiO3. And to the bioglass coating, the 45S5 bioglass coating made with PVA as filmogen agent heat-treated at 800? has the best film-substrate adhesion. The bioglass coatings are all polyporous, which is conducive to the improvement of bonding strength between bones and implants. Meanwhile, three different kinds of bioglass coating showed good biological activity after the biological tests.