GUIDED BONE REGENERATION

Bone regeneration is an exceptional coordination of biology and biomechanics that occurs in distinct temporal events, fine-tuned by a rich vascular cascade. The ultimate target of this highly complex process is the restoration of form and function of the original tissue type, which represents a significant medical challenge depending on the extent of bone insufficiency. In dentistry, such an insufficiency is often the result of tooth loss and is the major obstacle for traditional implant strategies. Several surgical procedures have been developed to contrast the bone loss and to secure the outcome of implant rehabilitation.Among these, Guided Bone Regeneration (GBR) requires the use of a membrane that is inserted between the bone defect and the soft tissue, and that was originally conceived to serve as a physical barrier in the attempt to prevent the migration and proliferation of epithelial and connective tissue cells into the bone compartment, thus allowing to harness the intrinsic regenerative capacity of bone.GBR is a surgical procedure that uses barrier membranes with or without particulate bone grafts or/and bone substitutes. Osseous regeneration by GBR depends on the migration of pluripotential and osteogenic cells (e.g. osteoblasts derived from the periosteum and/or adjacent bone and/or bone marrow) to the bone defect site and exclusion of cells impeding bone formation (e.g. epithelial cells and fibroblasts). To accomplish the regeneration of a bone defect, the rate of osteogenesis extending inward from the adjacent bony margins must exceed the rate of fibrogenesis growing in from the surrounding soft tissue.After GBR procedures, bone regeneration follows a specific sequence of events. Within the first 24 hours after a bone graft, the graft material/barrier created space is filled with the blood clot which releases growth factors (e.g., platelet derived growth factor) and cytokines (e.g., IL-8) to attract neutrophils and macrophages. The clot is absorbed and replaced with granulation tissue which is rich in newly formed blood vessels. Through these blood vessels, nutrients and mesenchymal stem cells capable of osteogenic differentiation can be transported and contribute to osteoid formation. Mineralization of osteoid forms woven bone, which later serves as a template for the apposition of lamellar bone. This transformation of primary sponge work would eventually constitute both compact and reticular bone with mature bone marrow. These events occur 3 to 4 months post-surgery.