EARLY TISSUE-RESPONSE TO TITANIUM IMPLANTS INSERTED IN RABBIT CORTICAL BONE .2. ULTRASTRUCTURAL-OBSERVATIONS

The tissue response to screw-shaped implants of commercially pure tita nium was studied 3-180 days after insertion in the rabbit tibia by mea ns of transmission electron microscopy. Red blood cells and scattered macrophages predominated at the implant surface after 3 days. At day 7 and later intervals, multinuclear giant cells were the cell type foun d at the implant surface protruding into the bone marrow and in areas with no bone-titanium contact. Osteoblasts or mesenchymal cells were r arely seen at the implant surface at any time period. Two modes of min eralization could be distinguished in the interface. Firstly, the typi cal mineralization of osteoid seams produced by osteoblasts. Secondly, an accumulation of scattered hydroxyapatite crystals in the unmineral ized collagen matrix in the interface. Mineralized tissue was observed close to the implants surface from day 14. However, the innermost 2-2 0 mum were poorly mineralized although scattered hydroxyapatite crysta ls were present. The collagen fibrils did not reach the implant surfac e but were separated from it by an amorphous layer, being 0.3-0.5 mum thick which did not decrease in width with time. An electron-dense lam ina limitans-like line containing mineral was observed between the amo rphous layer and the bone tissue.