Introduction

Bone grafts are used to facilitate bone formation within a given space by occupying that space and allowing the subsequent bone growth to take place.

These are bioresorbable and have no antigen-antibody reaction.

The mechanism that supports the bone graft materials are:

• Osteogenesis
• Osteoinduction
• Osteoconduction

Osteogenesis:

Here, the living osteoblasts are a part of bone graft material. With sufficient blood supply and cell viability, the osteoblasts in the bone graft material will form a new centre for ossification within the bone graft.

Osteoinduction:

Here, the bone graft material will stimulate the osteoprogenitor cells (undifferentiated mesenchymal stem cells) that are present within the defect or through blood supply, to differentiate into osteoblasts. These osteoblasts cause new bone formation.

This induction of bone formation occurs through various cell mediators usually bone morphogenic proteins (BMP's).

Osteoconduction:

Here, the bone graft material acts as a scaffold in which the osteoblasts from the defect undergo bone growth. They neither inhibit nor induce bone formation.

They simply allow the normal formation of bone by osteoblasts into the grafted defect along the surface of the graft material.

Ideal requirement of bone graft

• Osteoinductive property
• Non-toxic
• Resistant to infection
• No root resorption or ankylosis
• Non-antigenic and biologic compatibility
• Easily adaptable and available
• Predictability
• Strong and resilient
• Require minimal surgical intervention
• Rapid vascularization
• Should stimulate new attachment and be able to trigger osteogenesis.

Types of bone graft materials

1.   Autograft - derived from the same patient

2.   Allograft - derived from the same species

3.   Xenograft - derived from a different species

4.   Alloplast - synthetically produced materials

Autograft:

Extra oral: iliac crest, tibia, fibula, ribs

Intraoral: chin exotosis, ramus, and tuberosity.

On comparing cortical and cancellous autograft, cancellous autograft has the most osteogenic potential.

Cortical autografts can be used for implant stabilization.

Advantages: It is osteoconductive, osteoinductive and osteogenic.

Disadvantages: It requires another surgical site for harvesting.

Allograft:

Allograft bone is taken from cadavers that have donated their bone.

It requires sterilization and deactivation of proteins normally found in healthy bone.

• FDBA (freeze - dried bone allograft): it is osteoconductive.
• DFDBA (decalcified, freeze - dried bone allograft): it is osteoinductive because it retains some of the original BMPs within the donor tissue matrix.

Xenograft:

• Bovine derived
• Porcine derived
• Equine derived

Alloplast:

• Hydroxyapatite
• Beta tricalcium phosphate (Synthograft™, Cerasorb®)
• Bioactive glass (Perioglas® and Biogran®)
• Synthetic glass
• Calcium sulphate (calcium sulphate impregnated with tobramycin - Osteoset®)
• Porous Titanium Granules (Tigran™ PTG)

These materials combine with growth factors, ions such as strontium or mixed with bone marrow aspirate to increase biological activity.

The presence of elements such as strontium can result in higher bone mineral density (BMD) and enhanced osteoblast proliferation.

Alloplasts can be mixed with autografts or allografts in the management of large structural defects.

Some alloplasts are mixed together for superior results.

Example: Fortoss® Vital (beta TCP and calcium sulphate)

Classification of bone graft substitutes

• Allograft based
• Growth Factor based
• Cell based
• Ceramic based
• Polymer based

Growth factors based grafts:

They consist of either human growth factors or morphogens.

The groeth factors used are TGF-beta, insulin like growth factors I and II, PDGF, FGF, and BMPs.

Cell-based bone grafts:

Stem cells are cultured in the presence of dexamethasone, ascorbic acid, and β-glycerophosphate to direct the undifferentiated cell towards osteoblast lineage.

Ceramic-based bone grafts:

Calcium sulphate: it is biocompatible, bioactive, and resorbable after 30-60 days

Bioactive glass: it is biologically active silicate-based glass, high elastic modulus, and brittle

Calcium phosphate: includes Bio-Oss (hydroxyapatite as particulate) OsteoGraft (hydroxyapatite as blocks and particulate)

Polymer-based bone grafts:

It can be natural or synthetic polymers; degradable and non-degradable polymer.

Ex. Healos, Cortoss

Reference:

Newman and Carranza's Periodontology

Article - Bone Grafts in Periodontics - Balaji, V. R.; Manikandan, D.; Ramsundar, A.