Ultrastructural identification of cells involved in the healing of intramembranous and endochondral bones.

This study was designed to identify the cells involved in the healing of autogenous intramembranous (IM) and of endochondral (EC) bone grafts. Thirty-six defects were created in the skull of 18 adult New Zealand White rabbits. Defects were filled with IM graft alone, EC graft alone, demineralized bone matrix (DBM) alone, or combined DBM-IM and DBM-EC bone. Cellular identification was carried out at 7 and 14 days by light and electron microscopy. In IM bone, preosteoblasts, osteoblasts, and osteocytes were observed with no cartilage intermediate stage, while in EC bone, chondroblasts and chondrocytes were observed. DBM implant and DBM-IM were characterized by the presence of a cartilage stage. In conclusion, IM bone healed through an osteogenic ossification route, while EC bone healed through an EC ossification route. In the presence of demineralized EC bone matrix, IM bone adopts an EC ossification route.