Why do I need a bone graft for dental implants?

Being a specialist clinic, we get quite a number of patients who come to us for second opinions. Patients often seek second opinion when they don't quite agree with the diagnosis and/or treatment plan presented to them. Seeking a second opinion is good as it can either offer more options or affirm the initial opinion. With advances in technology, situations which were previously deemed unsuitable for dental implants are now possible. Bone grafting has enabled many patients who do not have sufficient bone to enjoy the benefits of having fixed teeth instead of dentures.

However, needing a bone graft means having an additional procedure and along with that, more time and potential complications. Hence, one of the common reasons for second opinions is to seek a graft-less approach.

The part of our jaw bone that holds the teeth is called the alveolar bone. Once teeth are extracted, the alveolar bone shrinks as it no longer has a function. The amount of bone loss increases with multiple extractions. And if you replace the missing teeth with a removable denture, the bone shrinks even faster. In the case of the upper jaw, the problem is compounded even more by the expansion of the maxillary sinus which is situated just above. As such, it is very common, especially in Asians, for the bone to shrink to a level where there is not enough bone to support a dental implant. This is where bone grafting comes in.

Bone can be grafted onto the shrunken jaw bone so that it can support an implant. There are many types of bone graft material and many methods of bone grafting.

Bone grafting material

Your own bone: The best bone graft material is your own bone. Bone can be harvested from other parts of your body and added on to the jaw bone. The common donor sites are the chin bone, hip bone, and leg (tibia) bone. The hip bone is very suited to be donor site because it is large and much bone can be harvested without causing a deformity in the hip. However, a general anesthetic is needed for this procedure which has to be done in an operating theatre either in a hospital or ambulatory surgery centre. This is usually done as a day surgery procedure, meaning, no overnight stay in the hospital. When there is minimal shrinkage of the jaw bone and the amount of graft material needed is less, smaller bones such as the chin or leg bone can be used as donor site. These sites can be accessed without the use of general anesthetic. However, in the case of the chin bone, there are nerves adjacent to it and there is a risk of numbness over the chin area. For the leg bone, only the "soft" part of the bone can be harvested. So, if you need a block of bone, some other site will be needed.

"Commercial" bone: For those who do not want to have a donor site surgery, a limited amount of bone grafting can be done by using commercially available bone. "Commercial" bone grafting material are harvested from human or animal donors. The bones are processed and sterilized and packed into sterile bottles for sale. Unlike your own bone, which is both conductive and inductive, ie can stimulate bone cell formation and allow it to grow in, "commercial" bone is only conductive; they do not have the ability to stimulate bone formation but merely facilitate the passage of bone through the graft. For relative small defects, there is no significant difference between the results of using your own bone compared with "commercial" bone. However, if the amount of graft needed is significant, using your own bone will give a better result. 

Many patients are concern about rejection of the graft. Techinically speaking, there is no rejection in the way that a kidney or liver transplant gets rejected. This is because these "commercial" bone are processed in such a way that only the mineral component is left and all the organic portions are removed. The graft can fail but it is not "rejection" per se but is due to lack of blood supply to the graft, wound breakdown, etc.

For those who are unwilling or unable to undergo the additional surgery to harvest their own bone but need a signficant amount of bone, recombinant human bone morphogenetic protein can be used. This is a protein that when applied to the receipient site, has the ability to stimulate bone formation like your own bone. It is, however, not a bone graft per se but rather a stimulant to bring about new bone formation. 

Grafting Methods

The bone graft material can be placed directly onto the jaw bone where augmentation is needed. However, such onlay grafts undergo a lot of resorption because it is difficult to get a good blood supply to the graft. Without a good blood supply, there is no supply of nutrients, oxygen and bone cells to "grow" bone. As such, onlay grafts can only be used in areas where the amount of grafting is minimal. 

A more predictable way of augmenting the deficient bone is by means of an inlay graft. This is done by separating the deficient bone into two and packing the bone graft material in between. This way, the blood supply to the graft is better preserved and the success of the graft is enhanced.

When the back part of the upper jaw lacks sufficient bone to anchor implants, it is often due to a process known as pneumatization of the maxillary sinus. To overcome this, a sinus lift procedure is done, This is done by lifting up the sinus membrane from the underlying bone and placing the bone graft material in between, This procedure has a very high success rate because the graft is enclosed within a area that is rich in blood supply and bone forming cells. 

Alternatives to bone grafting

Recent advances in implant component design has enabled some of the cases that need grafting to be done graftlessly. This is done by placing the implants in an angulated position to engage whatever bone is available and then use the newly developed components to correct the angulation of the implant when making the prosthesis. These usually applicable for patients who have lost all their teeth and would have needed a huge bone graft before they can have implants. This option is attractive in that it circumvents the need for bone grafting but it is not suitable for everyone. There must still be sufficient bone in strategic areas for this to be done. 

Bone grafting is a very common adjunctive procedure in dental implant treatment today. There are many options of bone grafting material and methods. What is needed is a proper diagnosis of the condition and the utilization of the appropriate material and method.