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 graft s. Thirty-six defects were created in the skulls of 18 adult New Zeala nd White rabbits. Defects were filled with IM graft alone, EC graft al one, 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, w hile in EC bone, chondroblasts and chondrocytes were observed. DBM imp lant and DBM-IM were characterized by the presence of a cartilage stag e. In conclusion, IM bone healed through an osteogenic ossification ro ute, while EC bone healed through an EC ossification route. In the pre sence of demineralized EC bone matrix, IM bone adopts an EC ossificati on route.