The Role of Osteoclasts in Demineralized Bone Powder Implants During the Angiogenetic Phase of Ossicle Formation

Demineralized bone powder (DBP), even implanted in ectopic sites, induces the formation of bone [1]. A cytokine referred to as bone morphogenetic protein, contained in bone matrix, triggers the bone formation, which is termed bone induction or osteoneogenesis. The implant is first invaded by undifferentiated or mesemchymal cells and is enclosed in a fibroblastic capsule (days 1–7 after implantation). The mesenchymal cells then differentiate into chondrocytes, which secrete cartilage matrix. Calcification of the matrix occurs (days 8–12). As in the formation of long bone, the cartilage is then invaded by blood vessels, a phase during which bone marrow cells begin to appear as well as osteoblasts in their most active form, which secrete osteoid (days 13–17). By day 20 the cartilage has completely disappeared. The result is the formation by day 30 of a cancellous ossicle encompassing bone marrow, in which, nevertheless, DBP particles are not resorbed.