48 Theories and techniques of oral implantology

   P-   'eratint;

   7sce   layer ,steum

Proliferating osteogenic cells

Fibrous layer of periosteum

A

B

Fig. 2-28. A, The microscopic appearance of a fracture in a long bone. Here is a longitudinal section cut through a rabbit's fractured rib. Forty-eight hours after the injury, the blood clot has formed between the two bone fragments. Dead bone, which can be distinguished by the empty lacunae, extends back a considerable distance from the fracture site. B, After 5 days, the cells of the thickened osteogenic layer of the periosteum have formed both cartilage and bone. They have lifted the fibrous layers of the periosteum away from the bone, and the typical picture of a cuff around the fracture site is seen. There is a sharp line of demarcation between the cartilage and the clot. C, After 7 days, osteogenic cells from the two collars have met, but not yet invaded the clot and begun to organize it. New bone is advancing both from the periosteum and from the marrow. The external callus has formed a tight cuff around the fracture. D, Two weeks later, cartilage is replacing bone. Portions of the clot are still to undergo organization and disintegration. (From Ham, A.: Repair and transplantation of bone. In Bourne, G. H., editor: Biochemistry and physiology of bone, New York, 1956, Academic Press, Inc.)