The material science of calcium phosphate ceramics.

Tricalcium, tetracalcium phosphate and hydroxyapatite ceramics exhibit distinct differences in their chemical and structural composition. Only hydroxyapatite ceramic is identical with the original bone mineral. Different preparation methods lead to compact hydroxyapatite ceramic or to porous material with interconnecting macropores as structural equivalents of the spatial structure of cancellous bone. Concerning the behaviour in a biological environment, high crystallinity and large material density result in resistance to dissolution and long lasting stability. Amorphous ultrastructure and porous formation enhance interface activity and bone ingrowth, but also biological degradation of the ceramic implant material.