Bioactive ceramic prosthetic coatings.

The concept of bioactive ceramic coatings on macroscopically smooth prostheses tries to reconcile opposing principles: the ceramic with beneficial bone tissue growth effects is used as a coating since it does not have sufficient strength and toughness to be used by itself as a prosthesis material. But strength is still an issue since the coating is the primary means of transferring stresses from prosthesis to surrounding tissues. The interface between the metal core and ceramic surface is then critical, since it essentially depends on the strength characteristics of the ceramic. Conversely, when the ceramic coating is used as a means to enhance bone-tissue formation around and into the prosthesis surface, thereby helping to establish a mechanical form of retention, the adhesion of ceramic coating to metallic substrate is not critical. The optimum characteristics of the ceramic are then those that produce the highest effect on bone-tissue growth rates immediately after surgery. The rate of bioactivity is related to the chemical reactivity of the material causing interfacial dissolution, precipitation, and ion exchange reactions. Furthermore, it also appears to depend on a substratum function affecting mineral precipitation, collagen deposition, and cellular differentiation and proliferation.