Light and electron microscopic studies of bone-titanium interface in the tibiae of young and mature rats

Bone-titanium contact was examined in young and mature rats on various days after insertion of pure titanium into the tibia. Under light microscopy, on the 14th day, lamellar mature bone was initially formed, and was seen to make direct contact with the titanium in both groups. In young rats on the 28th day, bone-titanium contact was greater than that in mature animals. On 1-micron sections, an amorphous zone 0.5-1.0 micron thick was found around the titanium, and a slender cell layer lay parallel to the implant, forming the superficial layer of the amorphous zone. Ultrastructurally, these slender cells were identified as osteoblastlike cells and made direct contact with the implant via a 20-50-nm thin amorphous zone. Below this cell layer, a collagen-containing, poorly mineralized zone was present and bordered by lamellar bone with a lamina limitans-like structure. However, this cell layer was absent in places, and therefore the thick amorphous zone without slender cell layer consisted ultrastructurally of a 20-50-nm thin amorphous zone and a poorly mineralized zone bordered by the lamellar bone. Sometimes this poorly mineralized zone was absent, and in such cases, the lamellar bone contacted the titanium by the thin amorphous zone formed on the lamina limitans-like structure. Thus, although bone was seen to make contact with the titanium implant, ultrastructurally a 20-50-nm thin amorphous zone, a slender cell layer, and/or a poorly mineralized zone were interposed between the bone and titanium.