What is bone graft in dentistry?

Bone graft is a material that used to replace missing bone or bone defect in the face and mouth region, particularly in jaw area for support of  implant during implant placement. Bone graft can also be use support the cheek or the chin area for aesthetic reasons.
Usage of bone graft in dentistry:

• Orthognathic (Corrective jaw surgery) Surgery
• Alveolar Bone Grafting (ABG) procedure in cleft patient
• Periodontal surgery (eg. Guided Bone Regeneration)
• In implant dentistry, bone grafts are widely used  in:
  • Sinus augmentation
  • To preserve the socket after dental extraction of implant placement later
  • To repair defect after dental extraction
  • To cover exposed implant fixture during implant placement

Bone augmentation is a term that describes a variety of procedures used to “build” bone so that dental implants can be placed.

When do we use bone graft in implant surgery?

Bone graft is used when there is not enough of bone at the site where implant is intended to be placed. Usually, when the width or the height of the jaw bone is not enough to support the placement of implant.
Bone graft can be obtain from outside or from patient’s own bone (autologous bone). Autologous bone is the best bone to substitute missing bone due to its high survival rate  and its capability of attract new bone formation.

Bone graft sources

Autograft (Autogenous Bone)

In implant dentistry, the usual site in the mouth that used to get bone graft (Donor site) usually depends on surgeon preference, the quality and quantity required:

• External oblique ridge (bone behind the lower last molar)
• Chin area
• Tuberosity (bone behind the upper last molar)

Advantages of autograft:

• Less rejection because graft originated from the patient’s own body
• The graft doesn’t carry any disease
• Using autograft bone as grafting material produce the highest successful outcome and predictability because the graft is a vital (living) bone which has the property of  osteoinductive and osteogenic, as well as osteoconductive to regenerate new bone.

Disadvantages:

• Additional surgical site is required (2 site surgery)
• Post-operative pain and complications

Allografts

Allograft bone, like autogenous bone, is derived from humans; the difference is that allograft is harvested from an individual other than the one receiving the graft. Allograft bone can be taken from cadavers that have donated their bone so that it can be used for living people who are in need of it.

There are three types of bone allograft available:

1. Fresh or fresh-frozen bone
2. Freeze-dried bone allograft (FDBA)
3. Demineralized freeze-dried bone allograft (DFDBA)

Allograft bone used in dentistry uses bone from cadaver that undergo process of removal of unwanted material such as fats, cells, antigens, and inactivates pathogens, while preserving the valuable minerals and collagen matrix. This material is than freeze-dried before package.
Advantages of allograft:

• Less antigenic rejection because allogaft bone originated from the same species
• No need additional surgical site is required (2 site surgery)
• The success of grafting using allograft will be lesser than autograft as the material used is basically a dead tissues
• However, this material still carry property of  osteoinductive and osteoconductive to regenerate new bone

Disadvantages:

• Allograft bone might carry certain unknown diseases that resist the cleaning process during preparation of the graft
• The graft usually resorb faster than xenograft material
• Additional cost to the surgery

Xenografts

Xenograft bone substitute has its origin from a species other than human, such as bovine bone (or recently porcine bone) which can be freeze dried or demineralized and deproteinized. This material still has the property of  osteoinductive and  osteoconductive to regenerate new bone.

Advantages of xenograft:

• No need additional surgical site is required (2 site surgery)
• This material still carry bone regeneration property of  osteoinductive and osteoconductive.
• However,  success of grafting using xenograft will be lesser than autograft as the material used is basically a dead tissues
• Xenograft material last longer in the mouth therefore, it with maintain the bone thickness for years

Disadvantages:

• Just like allograft, xenograft material might carry certain unknown diseases that resist the cleaning process during preparation of the graft
• Additional cost to the surgery

Alloplastic grafts

Alloplastic grafts may be made from hydroxylapatite, a naturally occurring mineral that is also the main mineral component of bone. They may be made from bioactive glass. Hydroxylapatite is a Synthetic Bone Graft, which is the most used now among other synthetic due to its osteoconduction, hardness and acceptability by bone.

Some synthetic bone graft are made of calcium carbonate, which start to decrease in usage because it is completely resorbable in short time which make the bone easy to break again.
Tricalcium phosphate which now used in combination with hydroxylapatite thus give both effect osteoconduction and resorbability.
Polymers such as some microporous grades of PMMA and various other acrylates (such as polyhydroxylethylmethacrylate aka PHEMA), coated with calcium hydroxide for adhesion, are also used as alloplastic grafts for their inhibition of infection and their mechanical resilience and biocompatibility. Calcifying marine algae such as Corallina officinalis have a fluorohydroxyapatitic composition whose structure is similar to human bone and offers gradual resorption, thus it is treated and standardized as “FHA (Fluoro-hydroxy-apatitic) biomaterial” alloplastic bone grafts.

Biological mechanism

Bone grafting is possible because bone tissue, unlike most other tissues, has the ability to regenerate completely if provided the space into which to grow. As native bone grows, it will generally replace the graft material completely, resulting in a fully integrated region of new bone. The biologic mechanisms that provide a rationale for bone grafting are osteoconduction, osteoinduction and osteogenesis.^[1]

Osteoconduction

Osteoconduction occurs when the bone graft material serves as a scaffold for new bone growth that is perpetuated by the native bone. Osteoblasts from the margin of the defect that is being grafted utilize the bone graft material as a framework upon which to spread and generate new bone. In the very least, a bone graft material should be osteoconductive.

Osteoinduction

Osteoinduction involves the stimulation of osteoprogenitor cells to differentiate into osteoblasts that then begin new bone formation. The most widely studied type of osteoinductive cell mediators are bone morphogenetic proteins (BMPs). A bone graft material that is osteoconductive and osteoinductive will not only serve as a scaffold for currently existing osteoblasts but will also trigger the formation of new osteoblasts, theoretically promoting faster integration of the graft.

Osteopromotion

Osteopromotion involves the enhancement of osteoinduction without the possession of osteoinductive properties. For example, enamel matrix derivative has been shown to enhance the osteoinductive effect of demineralized freeze dried bone allograft (DFDBA), but will not stimulate de novo bone growth alone.

Osteogenesis

Osteogenesis occurs when vital osteoblasts originating from the bone graft material contribute to new bone growth along with bone growth generated via the other two mechanisms.

More Info

• Problems with missing teeth
• Dental Implant – Introduction
• Dental Implant – In-Depth
• Bone Graft
• Dental Implant: A case of  Implant placement at the lower front jaw
• Dental Implant: A case of an Implant at the upper front jaw – immediate placement
• Dental Implant: A case of an implant placement over missing canine
• Computer Guided dental Implant Surgery
• Fear of Dental Treatment? How to overcome it..?

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