SCANNING ELECTRON AND LIGHT-MICROSCOPIC OBSERVATIONS ON THE HEALING-PROCESS AFTER SINTERED BONE IMPLANTATION IN RATS

The healing process after implantation of sintered bone in the rat par ietal bone was compared with that of synthetic hydroxyapatite using bo th scanning electron and light microscopy. The results showed that the differences between the sintered natural bone and the synthetic hydro xyapatite implantations were in the states of bone union and the biore sorbability of the implanted materials, even though both materials con sist of the same hydroxyapatite. In the sintered bone implantation, th e newly formed bone invaded into the material at 1 to 2 weeks after im plantation. The sintered bone surface on the dura mater side was compl etely covered by the new bone at 5 weeks. It is noteworthy that bone r esorbing areas characterized by Howship's lacunae were observed on the sintered bone surface at 2 weeks and the material was replaced by new bone. Light microscopy, which revealed the invasion and the developme nt of the new bone into the sintered bone, supported the scanning elec tron microscopic observations. In the synthetic hydroxyapatite, the ne w bone adhered closely to the material just like the sintered bone imp lantation. The new bone did not invade into the synthetic hydroxyapati te. There was no evidence of the resorption of the hydroxyapatite. Thi s shows that the natural and the biological structures of the sintered bone offer an advantageous environment to fluid circulation and ingro wth after implantation.