Low-temperature degradation in zirconia with a porous surface.

Today there is growing interest in zirconia in the dental field, but its use is still recent. Dental zirconia is mainly found in the form of yttria-stabilized zirconia crowns, bridges and abutments, and several companies are developing zirconia implants as an alternative to the standard biomedical grade titanium. In order to favor bone in-growth and osseointegration of zirconia implants, several strategies are now being explored to process rough and/or porous surfaces. The aim of this paper was to evaluate the resistance to environmental degradation of yttria-stabilized zirconia coated with a porous layer. We show that specific conditions of processing to generate the porous layer at the surface can lead to an accelerated tetragonal-monoclinic transformation of the porous layer in the presence of water. The impact of the transformation was evaluated in terms of structural integrity. Bending strength was not affected but the cohesion of the porous coating and its adhesion with the dense part deteriorated. We show that other processing conditions insure much better stability. Low-temperature degradation resistance of such porous surfaces should therefore be carefully followed and controlled in order to avoid critical problems in the future.