Autogenous Bone Versus Other Sources (Xenograft, Allograft, Alloplast)

The ideal bone graft should possess 3 qualities: osteoconductivity, osteoinductivity, and existing osteogenic cells. The presence of an osteoconductive matrix allows for vascular ingrowth and migration of osteoprogenitor cells into the graft site. This matrix can be composed of biologic or nonbiologic material and often is resorbed during the bone maturation process. Osteoinductivity speaks to the ability of graft components to stimulate native tissues to produce and/or recruit osteogenic cells. The presence of existing osteogenic cells in the grafted tissue allows for earlier de novo bone formation in the grafted tissue than if those cells were not present.

There are several possible sources for obtaining graft material for bone reconstruction. Allogeneic bone is donated cadaveric human bone. Potential donors are prescreened for communicable diseases and all bone that is ultimately donated is heat sterilized and freeze dried to remove all biologic components. This process, although it minimizes the potential for disease transmission and graft rejection, also eliminates the bone’s osteoinductive capacity and osteogenic cells. The graft retains its utility by functioning as an osteogenic scaffold. Xenograft material obtained from another species behaves similarly because all biologic material is eliminated during processing. A xenograft may be indicated over allogeneic bone in certain circumstances owing to its greater longevity. Alloplastic materials such as calcium sulfate, calcium phosphate and hydroxyapatite (S + A coral) are nonbiologic and have no intrinsic osteoinductive properties or osteogenic potential; however, they are biocompatible and function as an osteoconductive scaffold. Recombinant human bone morphogenic protein (BMP) 2 is a bioengineered version of a potent osteoinductive cytokine generally produced during normal bone healing. After reconstitution, the protein is delivered via a sponge to the proposed graft site. Although recombinant human BMP 2 is powerfully osteoinductive, the delivery medium has no bulk and therefore has no osteoconductive properties.

Autogenous bone is the gold standard material for bone grafting. Autogenous bone is the only graft material that contains intrinsic osteogenic potential through the always present osteoprogenitor cells. Naturally present BMP is the source of osteoinduction in living bone grafts. Of course, regardless of whether the graft used is cortical or cancellous, the solid nature of the graft provides an osteoconductive medium through which vascular ingrowth can occur and over which new bone growth can take place. The cellular and molecular elements that accompany autogenous bone graft serve multiple purposes. The first advantage is that the osteoconductive scaffolding recruits osteoprogenitor cells. This osteoconduction makes the autogenous graft more reliable and predictable. The second advantage of the autogenous bone graft is owing to its osteoinductive qualities derived from the molecular growth factors embedded in the autogenous graft. These factors include fibroblasts growth factors, transforming growth factor beta 1, vascular endothelial growth factor, and the BMP. These factors play an important role in new bone formation. This article discusses some of the most common autogenous sites for bone graft harvest and provides a guide for general practitioners. Each option carries its own limitations, such as volume constraints, donor site morbidity, and patient comfort.

To review, alloplasts, xenografts, and autografts all have osteoconductive properties; recombinant human BMP has osteoinductive properties. However, only autogenous bone grafts possess osteogenic potential and osteconductive and osteoinductive properties.

Autogenous Bone Versus Other Sources (Xenograft, Allograft, Alloplast)

The ideal bone graft should possess 3 qualities: osteoconductivity, osteoinductivity, and existing osteogenic cells. The presence of an osteoconductive matrix allows for vascular ingrowth and migration of osteoprogenitor cells into the graft site. This matrix can be composed of biologic or nonbiologic material and often is resorbed during the bone maturation process. Osteoinductivity speaks to the ability of graft components to stimulate native tissues to produce and/or recruit osteogenic cells. The presence of existing osteogenic cells in the grafted tissue allows for earlier de novo bone formation in the grafted tissue than if those cells were not present.

There are several possible sources for obtaining graft material for bone reconstruction. Allogeneic bone is donated cadaveric human bone. Potential donors are prescreened for communicable diseases and all bone that is ultimately donated is heat sterilized and freeze dried to remove all biologic components. This process, although it minimizes the potential for disease transmission and graft rejection, also eliminates the bone’s osteoinductive capacity and osteogenic cells. The graft retains its utility by functioning as an osteogenic scaffold. Xenograft material obtained from another species behaves similarly because all biologic material is eliminated during processing. A xenograft may be indicated over allogeneic bone in certain circumstances owing to its greater longevity. Alloplastic materials such as calcium sulfate, calcium phosphate and hydroxyapatite (S + A coral) are nonbiologic and have no intrinsic osteoinductive properties or osteogenic potential; however, they are biocompatible and function as an osteoconductive scaffold. Recombinant human bone morphogenic protein (BMP) 2 is a bioengineered version of a potent osteoinductive cytokine generally produced during normal bone healing. After reconstitution, the protein is delivered via a sponge to the proposed graft site. Although recombinant human BMP 2 is powerfully osteoinductive, the delivery medium has no bulk and therefore has no osteoconductive properties.

Autogenous bone is the gold standard material for bone grafting. Autogenous bone is the only graft material that contains intrinsic osteogenic potential through the always present osteoprogenitor cells. Naturally present BMP is the source of osteoinduction in living bone grafts. Of course, regardless of whether the graft used is cortical or cancellous, the solid nature of the graft provides an osteoconductive medium through which vascular ingrowth can occur and over which new bone growth can take place. The cellular and molecular elements that accompany autogenous bone graft serve multiple purposes. The first advantage is that the osteoconductive scaffolding recruits osteoprogenitor cells. This osteoconduction makes the autogenous graft more reliable and predictable. The second advantage of the autogenous bone graft is owing to its osteoinductive qualities derived from the molecular growth factors embedded in the autogenous graft. These factors include fibroblasts growth factors, transforming growth factor beta 1, vascular endothelial growth factor, and the BMP. These factors play an important role in new bone formation. This article discusses some of the most common autogenous sites for bone graft harvest and provides a guide for general practitioners. Each option carries its own limitations, such as volume constraints, donor site morbidity, and patient comfort.

To review, alloplasts, xenografts, and autografts all have osteoconductive properties; recombinant human BMP has osteoinductive properties. However, only autogenous bone grafts possess osteogenic potential and osteconductive and osteoinductive properties.

Onlay

Cortical blocks of bone are the most common form of onlay graft. Cortical blocks offer the benefit of the onlay autogenous bone grafting, a simple and well-used method that is successful and predictable if basic concepts are used and followed properly. Onlay grafts can be segmental or arched. These grafts can be used to restore both height and width of an atrophic and deficient area. These grafts are routinely used in maxilla and mandible in preparation of the site for implant placement. Indications for using the onlay cortical graft is as follows :

• 1.

  Inadequate residual alveolar ridge height and width to provide support for a functional prosthesis

• 2.

  Contour defects that compromise implant support, function, and esthetics

• 3.

  Segmental alveolar bone loss.

Graft healing

The most crucial operator-dependent steps in the survival of the graft are achieving graft stability and obtaining primary closure over the graft. It is not recommended to place the implant in the graft alone, because this is associated with a high failure rate. Therefore, a staged procedure is recommended to achieve better implant positioning after graft consolidation.

Management of graft tissue, preparation, and placement

The mucoperiosteal flap is designed in a way to adequately expose the underlying, deficient recipient site and maintain a base for vascular support and a tension-free primary closure. Usually, a midcrestal incision is preferred because it maximizes the vascularity to the margins of the flap and will minimize the ischemia. Labial vertical releases are made as needed for access. After exposing the entire alveolar process, gross bony irregularities should be made smooth to allow for maximum adaptation to the underlying alveolus. It is important that the size and contour of the graft be limited to what is needed to support the implants. Oversized or undersized grafts complicate soft tissue closure and interfere with planned prosthetic reconstruction. Upon completion of the grafting procedure, all voids and defects should be filled with particulate cancellous bone and marrow to provide good contour and to eliminate the dead space between the graft and recipient site. A primary, tension-free closure must be achieved to prevent wound breakdown and graft exposure, which will cause graft failure.

Risks, common complications, and management

• 1.

  Graft exposure owing to poor primary closure

• 2.

  Graft mobility

• 3.

  Donor site morbidity

• 4.

  Oversized or undersized graft

• 5.

  Infection

• 6.

  Poor osseous contact between graft and the recipient site

Cancellous Bone: Indications and Donor Sites

Cancellous bones have a wide scope of use because they can be placed within variety of alloplastic and allogenic materials, as well as reconstructive plates without any special instrumentation, long hospitalization, or high costs. Survival of harvested cancellous cellular bone allows the surgeon to transplant viable osteocompetent cells in to a well-vascularized tissue bed, ultimately resulting in a well-consolidated bone graft. Cancellous bone grafts respond favorably and predictably to transplantation as long as the recipient tissue bed is able to provide the metabolic needs of the implanted graft placed. Cancellous bone can be used in variety of procedures, such as socket preservation and sinus floor elevation grafting.

Socket Preservation

Cancellous bone can be used to preserve extraction sockets after an extraction in preparation for future implant placement. Extraction socket can be preserved and grafted by packing a mixture of alloplastic, allogenic, and/or xenograft bone. Gel foam or collaplug can be placed over the extraction socket to secure the graft material. One figure-of-8 suture can be placed with a 3.0 silk suture to secure the graft material. The extraction socket can be revisited in 3 to 4 months for placement of an endousseous implant.

Sinus Floor Elevation Graft

Cancellous bone can routinely be used for sinus floor augmentation. Mixture of autogenous cancellous, allogenic, and/or alloplastic bone could be used for sinus augmentation. After grafting, and average of 4 to 6 months is needed for proper graft maturation before implant placement.

• a.

  Onlay . Cancellous bone can be used to fill in the osseous gaps in onlay grafting.

• b.

  Ridge split . Cancellous bone can be used to fill in the osseous gaps in a split ridge.

Graft healing

In the late 19th and early 20th centuries, 2 conflicting theories of cancellous cellular bone healing existed. One was the osteoblastic theory, which originated with Ollier in 1867 and Axhausen in 1909. This theory was based on the belief that bone marrow and the periosteum survived implantation and produced bone. The induction theory originally by Phemister’s creeping substitution theory in 1914, which was expanded by Urist in 1953, held that transplanted bone did not survive the trauma of harvest. This theory proposed that the entire graft underwent an aseptic necrosis and was replaced by bone produced the connective tissue stem cells of the host–recipient bed or host–bone ends. Bone necrosis was linked with new bone formation. It is now known that the osteoblastic and induction theories of cancellous bone are not mutually exclusive. Current concept of cancellous cellular bone graft healing involves a 2-phased theory.