APATITE FORMATION ON 3 KINDS OF BIOACTIVE MATERIAL AT AN EARLY-STAGE IN-VIVO - A COMPARATIVE-STUDY BY TRANSMISSION ELECTRON-MICROSCOPY

Apatite formation on the surface of three kinds of bioactive material at an early stage after implantation in bone was studied using transmi ssion electron microscopy (TEM). The materials were apatite- and wolla stonite-containing glass-ceramic (A-W GC) as a surface-active glass-ce ramic, dense sintered hydroxyapatite (HA) as a surface-active ceramic, and dense sintered beta-tricalcium phosphate (beta-TCP) as a resorbab le ceramic. Particles of these materials, ranging from 100-300 mum in diameter, were implanted into rat tibiae, and specimens were prepared at 3, 7, 10, and 14 days after implantation. For A-W GC, dissolution o f the glassy and probably wollastonite phase was observed in the surfa ce region on and after the third day, and a collagen-free thin apatite layer on the surface of the material was evident on and after the sev enth day. This apatite layer was observed before the mineralization of the surrounding bone matrix and was sometimes evident even where the material bordered on the bone marrow. On and after the tenth day, the surrounding bone matrix calcified and A-W GC-bone bonding through an a patite layer was completed. For HA, a mineralized collagen-free layer was observed on the surface of the ceramic on and after the tenth day. This layer was always present near calcifying bone and it was difficu lt to distinguish from immature bone. For beta-TCP, such a surface min eralized layer was rarely evident, even just before bone-ceramic conta ct, and finally the bone bonded to beta-TCP directly. Cell-mediated de gradation of beta-TCP was frequently observed. In conclusion, surface apatite formation differed among these materials, reflecting their bio activity and suggesting differences in their bone-bonding mechanisms. (C) 1993 John Wiley & Sons, Inc.