Zirconia
implant abutments have gained popularity over the past few years as a
substitute for the traditionally used titanium alloy abutments. However,
research on the soft-tissue responses of zirconia and improving the zirconia
surface properties towards immediate soft-tissue integration are limited.

This
series of in
vitro studies aimed at evaluating tissue and cellular responses of
commercially available zirconia versus zirconia provided with sol-gel derived
TiO2 coating. Final purpose of the research project was to
optimize zirconia surface properties for fabrication of implant abutments,
which enhances gingival tissue attachment.

Coatings
were prepared from tetraisopropyl orthotitanate solution by dip-coating method.
The effect of coatings and the coating process on the mechanical properties of
zirconia was evaluated by biaxialflexural strength test. Human gingival
epithelial and fibroblast cell responses – adhesion kinetics, adhesion
strength, and proliferation– was studied in cell culture environment. Blood
response, including blood clotting ability, protein adsorption and platelet
adhesion and morphology was evaluated. A novel tissue culture method, developed
earlier by the research group, was used to evaluate porcine gingivaltissue
attachment on the coated and non-coated zirconia implants. Adhesion was
evaluated using routine microscopy coupled with immunohistochemical staining.
Furthermore, the strength of bond between tissue and implants was analyzed
utilizing dynamic mechanical analysis.

The
biaxial flexural strength of zirconia specimens was unaffected by the coating
process. Significant differences were observed in blood coagulation between the
coated and non-coated zirconia surfaces. UV treatment of the TiO2
coated
specimens enhanced blood coagulation. Blood platelets also appeared at a higher
activation state on coated specimens although no differences in protein
adsorption were observed. TiO2 coated zirconia were
significantly more hydrophilic with higher total surface free energy than
non-coated ones. Cell proliferation and adhesion was significantly higher on
coated specimens. Microscopic observation of gingival tissue attachment on
coated implants identified laminin-g-2 at the attachment of epithelium to implant indicating
direct attachment. This observation was absent in noncoated zirconia controls.
Furthermore, gingival tissue attachment to coated zirconia implants demonstrated
higher dynamic modulus of elasticity and higher creep modulus.

Sol-gel
derived TiO2 coatings on zirconia enhance trombogenicity and facilitate
direct gingival tissue attachment on zirconia surface. These findings indicate
that TiO2 coating on zirconia abutments has good potential to improve
implant treatment results.