Philosophy and Particulars of Autogenous Bone Grafting

SUMMARY Autogenous bone graft harvesting is a means to an end. The end product is, it is hoped, a restoration of jaw continuity that supports function via supporting prostheses and/or osseointegrated fixtures as well as standing up to functional loading over time. Today, particulate and cancellous marrow bone grafts are by far the most useful grafts because they transfer the greatest number of osteocompetent cells and can be shaped into the correct arch. Because they develop both a periosteum and an endosteum, they adapt, remodel, and even respond to growth as does normal bone. They are, therefore, more predictable and best support prosthetic rehabilitation. Alloplast reconstruction by itself is of only intermittent usefulness. Without a bone graft, it cannot support a prosthesis, and most become loose after several years. With a bone graft, alloplast trays and plates threaten perforation through skin or mucosa and may interfere with denture flanges or the placement of osseointegrated fixtures. Free microvascular transfers are attractive because they can transfer a complete boneperiosteum unit and soft tissue in a single stage. However, such free transfers of fibula, rib, and radius are no bigger than 11 mm in height and are straight tubular bones. They do not restore alveolar height, buccal width, or arch form well and, as such, do not retain osseointegrated fixtures in a useful pattern or under loading. Free transfers from the ilium are somewhat larger and serve reasonably well in the hemimandibular regions. Heowever, lack of arch form and bulkiness of soft tissue limit their use in the symphyseal area. On the horizon looms the potential of using bone morphogenetic protein (BMP-3, also called osteogenin; BMP-2; and BMP-7) to gain greater bone development from autogenous particulate bone transfers or perhaps eliminating them altogether. The science of bone regeneration clearly established osteogenin and several other bone induction proteins as capable of stimulated bone formation from undifferentiated mesenchyme. The challenges to bring this science to clinical surgery are several. First, osteogenin exists in small quantities in natural bone; about 20 jzg is obtained from 10 kg of bone. There-fore, synthesis by biochemical technologies or bacterial genetic engineering is required to produce useful amounts. Second, osteogenin placed in the usual scarred, irradiated, and otherwise compromised tissue recipient sites often does not contain sufficient mesenchymal cells that can respond. Third, there remains a concern about blocking antibodies or local inhibiting factors that reduce the bone-stimulating capabilities of osteogenin. Fourth, osteogenin does not work alone in vivo. It is part of a coordinated skeletal regenerative sequence that includes many other factors such as transforming growth factor-/3, macrophage-derived angiogenesis factor, platelet derived growth factor, and osteoclast activating factor. The timing, release, and interaction with these other factors have not yet been determined. Last, concern exists about systemic absorption of administered osteogenin and, therefore, bone stimulation in unwanted sites such as joints, lung, and myocardium. Because bone induction is a promise that may be several years away from common clinical usefulness, the reconstructive oral and maxillofacial surgeon of today has little choice but to be knowledgeable and experienced in the art and science of bone grafting and the approach to graft harvesting.