Three terms may be used to describe individual aspects of bone formation process that can occur around implants. They are Osteoconduction, Osteogenesis and Osteoinduction. In addition a fourth term Osteopromotion refers to the clinical promotion of Osteogenesis beneath barrier membranes (membrane which exclude soft tissue infiltration) for guided bone regeneration.
Osteogenesis
The term osteogenesis describes essentially two distinctly different phenomena by which bone can become juxtaposed to an implant surface.
Osteogenesis
The term osteogenesis describes essentially two distinctly different phenomena by which bone can become juxtaposed to an implant surface.
Distant Osteogenesis: In this an extracellular matrix establishes the implant surface contact. The osteogenic cells line the host bone surface. The blood supply to these cells is between the cells and the implant and bone is laid down on the host bone surface. The implant surface will always be partially obscured from bone by intervening cells and the general connective tissue extracellular matrix. This type of healing has also been described to explain the phenomenon of “Osseointegration” of machined metallic implants. In distance osteogenesis, new bone is formed on the surfaces of old bone in the peri-implant site. The bone surfaces provide a population of osteogenic cells that lay down a new matrix which encroaches on the implant. In this, new bone is not forming on the implant, but the latter does become surrounded by bone and the implant surface will always be partially obscured from bone by intervening cells.
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| Distant Osteogenesis |
Cortical bone can be expected to show distant osteogenesis as vascular disruption of the cortex caused during implant site preparation is known to lead to death of the peri-implant cortical bone and its subsequent slow remodeling by osteoclast invasion from the underlying medullary compartment. Therefore, distance osteogenesis will result in bone approximating the implant surface.
Contact Osteogenesis: In this the osteogenic cells attach to the implant surface and the new (de novo) bone is formed on the implant surface first. The developing bone matrix can directly interlock within the surface morphology. Since, by definition, no bone is present on the surface of the implant upon implantation, the implant surface has to become colonized by bone cells before bone matrix formation can begin. Optimization of contact osteogenesis can be done by implant design to ensure early stability (Primary stability) and a surface conducive to the attachment of the osteoblasts
Contact Osteogenesis: In this the osteogenic cells attach to the implant surface and the new (de novo) bone is formed on the implant surface first. The developing bone matrix can directly interlock within the surface morphology. Since, by definition, no bone is present on the surface of the implant upon implantation, the implant surface has to become colonized by bone cells before bone matrix formation can begin. Optimization of contact osteogenesis can be done by implant design to ensure early stability (Primary stability) and a surface conducive to the attachment of the osteoblasts
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| Contact Osteogenesis |
Contact Osteogenesis is the desired tissue response leading to firm osseointegration..It results in bone apposition to the implant surface.
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 phosphate ions 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. Bone remodeling:Following the initial osteogenesis, widespread cellular activity at the implant bone interface leads to the formation of trabacular structures along the collagen fibers. Depending on the early stages of cell attachment, proliferation and differentiation, the remodeling will eventually result in mature new bone.
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 phosphate ions 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. Bone remodeling:Following the initial osteogenesis, widespread cellular activity at the implant bone interface leads to the formation of trabacular structures along the collagen fibers. Depending on the early stages of cell attachment, proliferation and differentiation, the remodeling will eventually result in mature new bone.
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