Stages of Contact Osteogenesis
Osteoconduction: This is the first and the most important healing phase and relies on the recruitment and migration of osteogenic cells to the implant surface, through the residue of peri-implant blood clot. Fibrin attaches to the surface of the implant. Osteogenic cells bind to the fibrin. The firm adhesion of this fibrin network to the surface is necessary to prevent disruption of the fibrils from the surface during contraction of the blood clot, thus maintaining continuous contact guidance for the osteoblast migrating to the surface. The 3- D surface morphology determines the degree of cell attachment, quantity and time.
De novo bone formation:This is the second healing phase which results in a mineralized interfacial matrix equivalent to that seen in the cement line in the natural bone tissue.
It is the common factor linking normal tunneling remodeling and contact osteogenesis in which bone is formed for the first time at the appropriate site by the differentiating osteogenic cells. These are cells which have migratory capacity but will still become osteoblast. Clearly an essential prerequisite of de novo bone formation is that bone cells must first get to either the old bone or implant surface respectively, before extracellular matrix synthesis is initiated. At first the osteoblasts adhere to the surface. Surrounded in a collagen matrix made of organic phosphate, they release phosphateions until the solubility of calcium phosphate has exceeded and crystallized to hydroxyapatite. Surface morphology as well as the existence of calcium and phosphate ions on the implant surface determines the speed of bone formation.