Biodegradation behavior of various calcium phosphate materials in bone tissue.

In order to study the biodegradation behavior of calcium phosphate materials, cylinders of standard size were implanted in the tibiae of rabbits. Material parameters were stoichiometry (hydroxyapatite with a Ca/P ratio of 1.67 versus tricalcium phosphate with a Ca/P ratio of 1.50), crystallographic structure (apatite versus beta-whitlockite), microporosity, and macroporosity. The extent of biodegradation was evaluated by radiography, light and fluorescence microscopy, microradiography, and porosity measurements. All calcium phosphate materials were biocompatible in bone tissue. Hydroxyapatite ceramics had a higher osteogenic potential than beta-whitlockite materials. Depending on their porosities, sintered tricalciumphosphate (beta-whitlockite) materials were more or less biodegradable, in contrast to sintered hydroxyapatite materials, which showed no detectable resorption over a period of 9 months of implantation.