M. Richard et al., ULTRASTRUCTURAL AND ELECTRON-DIFFRACTION OF THE BONE-CERAMIC INTERFACIAL ZONE IN CORAL AND BIPHASIC CAP IMPLANTS, Calcified tissue international, 62(5), 1998, pp. 437-442
We investigated the influence of natural coral implants used as a bone
substitute on the quality of bone ingrowth in rabbits 2, 3, and 6 wee
ks after implantation. Explants were characterized by transmission ele
ctron microscopy and electron diffraction. Bone ingrowth has been prev
iously demonstrated by light microscopy, however, few have been perfor
med in electron microscopy to compare mineralized tissue ingrowth in c
oral implants which occurs at the expense of calcium carbonate to that
of calcium phosphate (CaP) implants. The interface between coral arag
onite and mineralized tissue or bone was abrupt, with no invasion of t
he aragonite structure by newly formed crystals, as occurs in micropor
es when biphasic CaP (BCP) ceramics were used. The restoring process a
ppears to be different from that induced by BCP implants. Precipitatio
n of needle-like apatite crystals on the CaCO3 implant surface was not
observed. Instead, apatitic smooth-shaped crystals formed in aggregat
es. The coral dissolution process does not release phosphate and so pr
ecipitation of apatite does not occur in the micropores of the coral i
mplant, thereby limiting the formation of an apatite layer and hence b
one bonding to the outer surface of the implant. In addition, on the o
uter surface of the implant, close to bone and a phosphorus source, th
e CaP crystals that do form are in aggregates presumably due to the ca
rbonate and mismatch between the aragonite and the apatite. This seems
to result in a delayed bone attachment or weaker bone bonding than Ca
P implants which encourage an epitaxial biological crystal deposition.