Allogenic Bone Grafts: Types, Biology, and Clinical Applications
Bone grafting is a foundational component of modern oral and maxillofacial surgery, implant dentistry, and reconstructive procedures. Among the available grafting options, allogenic bone grafts—derived from human donors—are widely used due to their availability, safety profile, and predictable biologic behavior. Understanding how different types of allogenic bone grafts incorporate, remodel, and support new bone formation is essential for proper material selection and long-term clinical success.
What Is an Allogenic Bone Graft?
An allogenic bone graft is harvested from a human donor and processed to remove cellular components while preserving the mineral and protein matrix. These grafts do not contain living cells at the time of implantation but serve as a scaffold and biologic stimulus for host bone regeneration. Their incorporation depends on the graft’s structure, processing method, and biologic activity.
Cortical Allogenic Bone Grafts
Cortical allografts are dense and structurally rigid, providing mechanical stability in grafted sites. These grafts are incorporated primarily through a process known as creeping substitution, in which host bone gradually replaces the graft material over time.
Bone formation in cortical allografts occurs predominantly through intramembranous ossification. Because of their density, cortical grafts remodel more slowly than cancellous grafts, making them useful in situations where space maintenance and structural support are required. However, their slower remodeling means delayed replacement with vital host bone.
Cancellous Allogenic Bone Grafts
Cancellous allografts are more porous and biologically active than cortical grafts. Their incorporation occurs through a two-phase process. First, host mesenchymal stem cells migrate into the graft and differentiate into osteoblasts. Second, osteoclasts resorb portions of the graft, exposing embedded bone morphogenetic proteins (BMPs), which further stimulate osteoblast activity and new bone formation.
Because cancellous grafts contain more exposed surface area and allow greater cellular infiltration, they are considered more osteogenic and osteoinductive than cortical allografts. This enhanced biologic activity results in faster remodeling and more robust new bone formation, making cancellous allografts ideal for many implant and ridge augmentation procedures.
Demineralized Freeze-Dried Bone Allograft (DFDBA)
Demineralized freeze-dried bone allograft undergoes processing that removes the mineral component while preserving organic matrix proteins, including BMPs. As a result, DFDBA remodels more rapidly and demonstrates greater new bone formation compared to mineralized grafts.
DFDBA is considered osteoinductive, meaning it actively promotes bone growth by recruiting host mesenchymal stem cells and stimulating their differentiation into osteoblasts. Preservation of BMPs is the key factor underlying its osteoinductive properties. DFDBA is commonly used when accelerated bone regeneration is desired.
Mineralized Freeze-Dried Bone Allograft (FDBA)
Mineralized freeze-dried bone allograft retains its mineral content and therefore remodels more slowly than DFDBA. Its primary function is osteoconduction, providing a scaffold that allows blood vessels and bone-forming cells to migrate into the grafted area.
FDBA is often selected when space maintenance is critical, such as in ridge preservation or sinus augmentation procedures, where maintaining volume over time is essential.
Fresh Frozen Allograft
Fresh frozen allograft is processed to preserve its mineral structure but does not contain viable donor cells. It functions primarily as an osteoconductive material, providing a lattice framework that supports vascular and cellular invasion from the host bone.
Xenografts
Xenografts are derived from non-human species, most commonly bovine sources. These materials are only osteoconductive. They serve as a scaffold for bone ingrowth but do not actively stimulate bone formation through growth factors or cellular recruitment. Xenografts are frequently used when long-term volume stability is desired, often in combination with other graft materials.
Key Biologic Principles of Bone Grafting
Understanding bone graft behavior requires familiarity with three fundamental biologic mechanisms:
Osteogenesis refers to the formation of new bone by living cells contained within the graft. This process only occurs with autografts, as allogenic and xenogenic grafts do not contain viable donor cells.
Osteoinduction involves the recruitment of host mesenchymal stem cells and their differentiation into osteoblasts through growth factors such as BMPs. Demineralized allografts are the primary graft type with osteoinductive capability.
Osteoconduction describes the ability of a graft material to act as a scaffold that facilitates vascular invasion and bone cell migration. All bone grafts—autografts, allografts, and xenografts—exhibit osteoconductive properties to varying degrees.
Clinical Significance in Oral Surgery and Implant Dentistry
Selecting the appropriate bone graft material depends on the clinical scenario, including defect size, need for volume maintenance, healing time, and implant timing. Allogenic bone grafts offer a versatile balance between biologic activity and structural support without the morbidity associated with autogenous bone harvesting.
A thorough understanding of graft biology allows clinicians to tailor graft selection for predictable outcomes in ridge augmentation, sinus lifts, socket preservation, and reconstructive surgery.
Conclusion
Allogenic bone grafts remain a cornerstone of contemporary bone regeneration. Differences between cortical and cancellous grafts, mineralized and demineralized processing, and their respective osteoconductive and osteoinductive properties directly influence clinical outcomes. By understanding how each graft type incorporates and remodels, clinicians can optimize bone regeneration and long-term success in surgical and implant-based procedures.
