FORMATION OF A CALCIUM PHOSPHATE-RICH LAYER ON ABSORBABLE CALCIUM-CARBONATE BONE-GRAFT SUBSTITUTES

The use of natural coral as a bone graft substitute is common in Europ e, However, the bone-coral bonding mechanism remains elusive. A rat su bcutaneous model was used to demonstrate changes at the surface of res orbable calcium carbonate in the form of natural coral. Histological r esults indicated in vivo formation of a calcium phosphate (CaP)-rich l ayer on the surface of the coral confirmed by backscattered electron i maging and X-ray microanalysis. There appears to be a combination solu tion-mediated dissolution/cell-mediated degradation of the natural cor al with subsequent surface conversion or precipitation. The end result is a CaP-rich layer on the coral. Though this layer has been observed previously, it was originally thought to be a histological artifact. This result is similar, however, to what is seen with Bioglass and gla ss ceramics and may also explain the good bonding of bone to hydroxyap atite. The fact that this layer is also present on natural coral after implantation in soft tissue sites may explain the intimate bone appos ition observed when natural coral is placed in bony sites.