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Bone defects in the craniomaxillofacial skeleton vary from the small (few millimeters) periodontal defects to the large segmental defects resulting from trauma, surgical excision, or cranioplasty. Such defects typically have complex three-dimensional structural needs, which are difficult to restore. In cranial vault defects, the underlying brain needs permanent protection. Segmental jaw defects require restoration of mechanical integrity, temporomandibular joint function, and intermaxillary dental occlusion. Maintaining acceptable facial esthetics is another unique consideration in the treatment of facial defects, which cannot be underestimated. Bone grafts remain the gold standard for reconstructing segmental bone defects. The earliest report of a bone grafting procedure came in 1682 by Job Janszoo van Meekeren, a surgeon in Amsterdam. In this account, the author reported a case in Russia, where the surgeon restored a cranial defect using a cranial bone graft from a dead dog. In 1881, Sir William MacEwen of Rothesay, Scotland, published the first case report of successful interhuman transfer of bone grafts. He used tibial bone wedges excised from three donors, during surgical correction of skeletal deformity, to reconstruct a humeral defect in a 3-year-old child. Subsequent clinical reports helped establish the efficacy of autogenous bone grafts in defect reconstruction. The term "bone graft" was defined by Muschler (Bauer, 2000) as: "any implanted material that alone or in combination with other materials promotes a bone healing response by providing oteogenic, osteoinductive or osteoconductive properties." An osteogenic material can be defined as one that has inherent capacity to form bone, which implies to contain living cells that are capable of differentiation into bone cells. An osteoinductive material provides biologic signals capable to induce local cells to enter a pathway of differentiation leading to mature osteoblasts. An osteoconductive biomaterial provides a three-dimensional interconnected scaffold where local bone tissue may regenerate new living bone. However, osteoconductive biomaterials are unable to form bone or to induce its formation. Another property that is interesting to find especially in bone substitutes is biodegradability. This is defined as the capacity of degradation of a particle by two mechanisms principally; through a passive chemical degradation or dissolution, and through active cellular activity mediated by osteoclast and/or macrophages. Moreover, the biological properties of bone substitute biomaterials are also influenced by their porosity, surface geometry and surface chemistry. The events leading to bone healing and regeneration are influenced by all the variables mentioned above. These properties are related to the biomaterial itself, however, host factors such as bone quality, vascularity of the graft bed and tobacco addiction may also influence the final outcome of a bone regeneration procedure with a bone substitute.
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