OSTEOGENIN-ENHANCED BONE-SPECIFIC DIFFERENTIATION IN HYDROXYAPATITE ORBITAL IMPLANTS

Hydroxyapatite orbital implants undergo early ingrowth of fibrovascula r tissue after enucleation. This animal study determined whether contr ol and osteogenin-impregnated hydroxyapatite orbital implants vary in their osteogenic response at 6 and 52 weeks. Rabbits underwent enuclea tion with implantation of control or osteogenin-impregnated hydroxyapa tite spheres. Light microscopy determined fibrovascular ingrowth, and histomorphometry quantitated the amount of bone produced. Osteogenin i mplants vascularized at a faster rate and contained bony foci by 6 wee ks that became confluent at 1 year. Spontaneous osteogenesis was not s een in control animals at 6 weeks. After 1 year they contained bone, a lthough less than in the osteogenin implants. Mixed cell inflammation was observed at the hydroxyapatite-tissue interface in both groups. No inflammation was noted at the interface of hydroxyapatite and bone. T hese are the first controlled observations that bone-specific differen tiation occurs in the pores of spherical hydroxyapatite implants withi n the soft tissues of the socket. This vascularized process can be enh anced with osteogenin to occur earlier and more uniformly in the impla nts at one year.