Dental bone grafting is most often used to fill jaw bone defects created by tooth extractions or to replace bone that has resorbed after historic extractions in order to be able to place dental implants.
Advances in recent years have made many such grafting processes possible, but is it all good news? To examine that issue you first need to understand a little about bone and the principles behind bone grafting.
The anatomy of jawbone
Bone typically has a strong, compact outer surface and contains cancellous or spongy bone within. In the case of the jaws, the mandible is a separate bone and so has a thick outer plate of compact bone. Whereas the upper jaw (being part of the skull) has only a thin outer bony plate and contains more cancellous bone – although the quantity of this bone can be compromised by the presence of other adjacent structures such as the sinuses and nose.
Typically the upper jaw has a good blood supply which is derived from multiple sources whereas the mandible has one main artery serving each side of the lower jaw which can become compromised and so has a poorer blood supply.
Bone is a dynamic tissue which is constantly being remodelled by cells known as osteoclasts which resorb bone and cells known as osteoblasts which deposit bone as shown in this short animation.
In general bone is thought to be able to remodel completely over time, but it requires some sort of scaffold in order to be able to do so unless the defect is very small.
Types of bone graft
There are several categories of bone graft which may be:
Autologous This is bone harvested from the patient’s own body.
Allograft This term is used for tissue from the same species, and is usually obtained from a cadaver or from a bone bank.
Xenograft A xenograft is tissue taken from another species, most often a pig or cow.
Synthetic These are substances made of hydroxyapatite or other naturally occurring and/or biocompatible substances that have similar mechanical properties to bone.
All these grafts are believed to act as an initial scaffold and to be resorbed and replaced as the natural bone heals over a period of a few months. They literally act to enable the osteoblast cells to be able to span any defect depositing new bone.
To see the ways in which such grafts are used, watch this short Dental Bone Grafting video.
The principles of bone grafting
The principles involved in successful bone grafts include:
Osteoconduction this refers to guiding the growth of new bone.
Osteoinduction is the inducing of undifferentiated cells to become active osteoblasts.
Osteogenesis refers to the grafting of supposedly living bone.
Autologous bone grafting in dentistry
In dentistry autologous bone grafts may involve taking bone from another site in the mouth, the chin, the coronoid process of the mandible, the hip (iliac crest), or the skull plates for major reconstructive or implant surgery. The advantage is that the bone is less likely to be rejected or to be the source of any infection because it originated from the owner.
It can be used as a block to build a deficient area or as particulates to fill a defect. Sometimes block bone grafts are screwed into place and these screws left in situ permanently or later recovered. When using particulated bone, the dentist may also use membranes.
These membranes are fine meshes that allow fluids to circulate and the graft to establish while containing it and preventing the gum tissue (which grows much faster than bone) from filling the defect. The membrane is usually removed at a later date when it has served its purpose of enabling bone to establish underneath.
Autologous grafts are osteoinductive and osteogenic, as well as osteoconductive. However, a second surgical site is involved and, as anyone who has had an iliac crest graft will tell you, it is the donor site that is most painful and takes the longest time to heal.
Infections of bone can be particularly persistent and difficult to resolve and some dentists express concern about electively creating an additional bony wound at a donor site for such procedures. In the case of a graft derived from the cancellous bone of the iliac crest then this may be osteoinductive and osteogenic, without providing the solid structure for new bone formation (osteoconduction).
However, in spite of the advantages such grafts appear to offer, recent research by Dr Hal Huggins DDS MS which he presented at the October 2012 meeting of the International Academy of Biological Dentistry and Medicine (IABDM) has cast doubt upon the wisdom of using even autologous bone grafts. According to his research, within a few seconds of severing the blood supply to such bone it becomes necrotic.
Bone allografts in dentistry
An allograft is material derived from another individual and is frequently harvested from cadavers or from people undergoing surgery such as hip replacements who donate the head of the femur to a bone bank. These grafts are usually freeze dried and may also be demineralised.
Freeze dried bone can be cleaned using a variety of methods including the use of gamma radiation, ultrasound, centrifuging, biological detergents, alcohol and hydrogen peroxide. Donors are screened by asking for their name, address, and whether they are HIV positive or have hepatitis C viruses. However, screening is minimal and the US Centers for Disease Control (CDC) have declared that ‘aseptically processed tissue should not be considered sterile’.
Ozone has also been used to treat human bone graft and although it may reduce pathogens it may also leave the most virulent species to survive according to Dr Huggins. In addition, he had found that many of the toxic metals used in dentistry can make such microbes much more dangerous. The copper found in dental amalgam fillings and some other alloys, for example, has been shown to promote the pathogenicity of bacteria at tiny concentrations.
According to his DNA analysis of supposedly sterile human cadaver and bovine bone used for grafting, samples tested have revealed as many as 56 different pathogens.
I have twice refused recommended blood transfusions in recent years because of concerns about receiving donor tissue. In my opinion, we simply don’t understand all the ramifications of using such tissue (prions, foreign DNA, possible infection, etc) at this time and I was keen to avoid it unless my life had depended upon it. In addition, when grafting materials derived from animal sources there is the potential for transfer of animal borne diseases and the introduction of foreign proteins and DNA to the human body.
Synthetic bone grafts
Synthetic bone grafting materials manufactured from ceramics such as calcium phosphates (e.g. hydroxyapatite and tricalcium phosphate), Bioglass and calcium sulphate and are all biologically active to different degrees. Such materials can then be treated with growth factors, ions such as strontium or mixed with bone marrow aspirate to increase biological activity.
And, although such grafts can be guaranteed free of the possible risk of infection posed by allografts, they are also using substances that are foreign to the body.
There is a concern among some dentists that although bone may appear to form at the site of such grafts, that this may effectively be the body trying to ‘wall off’ the grafted tissue. And whilst this form of bone may fulfil the role of supporting an implant, this bony scar tissue may be far from ideal in other regards.
As ever, it is important to make an informed choice because it is you who will have to live with the consequences.
Thoughts about promoting bony healing
As always, an ounce of prevention is worth a pound of cure. So it is worth knowing how to optimise healing at extraction sites in order to avoid the later necessity for a bone graft if possible.
The way nature intended healing to occur is that a blood clot forms and progenitor cells migrate into the clot transforming into osteoblasts. For this reason it is particularly important to ensure there is a blood clot present after any extractions and follow instructions about after care.
On the dentist’s part, it is considered advisable when having particularly a lower tooth extracted to use an adrenaline-free (epinephrine-free) local anaesthetic which will allow bleeding of the socket to occur. Removal of the periodontal membrane using irrigation and a round bur in a slow handpiece also allows for the site to heal properly with bone.
After an extraction, Dr Hal Huggins advises travelling no more than 3 miles maximum because experience has shown that travelling longer distances tends to break down the fragile structure of the blood clot affecting bony healing.
Some suspect that the abrasive agents used in toothpaste can settle within the healing socket potentially causing long term problems. So use either salt and/or hydrogen peroxide or one of the essential oil blends (or no toothpaste at all) to clean your teeth while the wound is healing.
Dietary advice for promoting bony healing includes eating sufficient high quality protein for repair and ensuring it is being digested properly by taking digestive enzymes if necessary. Supplementing digestive enzymes for a period of time may also help to promote meridian flows particularly in relation to the posterior teeth (which are all on meridians associated with digestion).
According to Dr Weston Price, eating foods rich in fat soluble vitamins and particularly what he referred to as Activator X which is now believed to be vitamin K2 was of particular importance to bony healing. You can obtain such vitamins by eating plenty of high vitamin butter from grass fed cows which is available from specialist suppliers. Failing that, eat the yellowest butter you can find and you can also supplement the required fat soluble vitamins in the form of Green Pasture’s Royal Butter Oil/Fermented Cod Liver Oil Blend.
Finally, new regenerative methods using platelet-rich plasma and other specially treated fractions of the patient’s blood are now starting to be used by some dentists and surgeons to promote proper bony healing at extraction sites.