What is a Bone Graft?
A bone graft is a surgical material used to increase bone volume or serve as a tissue scaffold for bone formation, available in block or particulate forms, and classified into four main categories based on origin: autografts (from the patient), allografts (from donors), xenografts (from animals), and alloplasts (synthetic materials). 1, 2
Primary Classification by Origin
Bone grafting materials are categorized based on their source and biological properties:
Autografts (Patient's Own Bone)
- Autografts are considered the "gold standard" for bone grafting because they possess all three critical biological properties: osteogenesis (living bone cells that form new bone), osteoinduction (growth factors that stimulate bone formation), and osteoconduction (scaffold for bone growth). 2, 3, 4
- Autografts contain viable osteoprogenitor cells that directly contribute to new bone formation. 2
- The main disadvantage is donor site morbidity, with 34% of patients reporting harvest site pain. 2
- Common donor sites include the mandibular symphysis, ramus, retromolar area, and iliac crest. 1
Allografts (Donor Bone)
- Allografts lack osteogenic properties (no living cells) but retain some osteoinductive potential, particularly with demineralized bone matrix. 2
- They offer convenience, abundance, and eliminate donor site morbidity. 3
- Allografts are associated with higher non-union rates and significantly increased graft collapse (30%) compared to autograft (5%) in multiple-level procedures. 2
- Healing time for allograft block grafts is 5-6 months before implant placement. 2
Xenografts (Animal-Derived)
- Xenografts are commonly bovine or porcine materials used in clinical practice. 2
- They provide osteoconductive properties but lack osteogenic and osteoinductive capabilities. 1, 5
Alloplasts (Synthetic Materials)
- Alloplasts provide an osteoconductive scaffold for bone growth. 2
- Common examples include calcium phosphate and calcium sulfate synthetics. 3
- Generally not recommended for vascular applications due to infection risks. 2
Physical Forms of Bone Grafts
Block Grafts
- Block grafts are solid pieces of bone used for significant bone volume augmentation, requiring 4-6 months healing for autografts and 5-6 months for allografts, with expected lateral bone gain of 4-6 mm. 1, 2
- Block autografts are typically combined with particulate bone grafts and barrier membranes to reduce resorption risk. 1
Particulate Grafts
- Particulate grafts are morselized (ground) bone used alone or combined with other materials. 1, 2
- They can be harvested from adjacent or secondary surgical sites, with the mandibular retromolar region being the most common donor site. 1
- Particulate autografts typically require 6-8 months healing time before implant placement. 1
Clinical Applications and Purpose
Bone grafts serve three primary purposes in surgical procedures: 1
- Increase bone volume in areas of deficiency for procedures like dental implant placement, spinal fusion, or fracture repair. 1
- Serve as a tissue scaffold that provides a framework for the patient's own bone cells to grow into and eventually replace. 1
- Deliver osteogenic cells (in the case of autografts) that directly participate in new bone formation. 2, 4
Important Clinical Considerations
Factors Affecting Graft Success
- Smoking has a more significant negative impact on fusion success with allograft versus autograft. 2
- The type of graft, site of transplant, quality of transplanted and host bone, host bed preparation, and mechanical properties all influence graft incorporation. 4
- Osteogenesis is ultimately induced by the host and is site-dependent, regardless of the bone graft material used. 1
Adjunctive Materials
- Barrier membranes create physical space for osteogenic cells to regenerate bone while excluding non-osteogenic cells like epithelial cells and connective tissue fibroblasts. 1
- Bioactive modifiers (such as platelet-rich fibrin or growth factors) can enhance healing and proliferation of osteogenic cells or blood supply. 1