When dental implants have become the treatment of choice for replacing missing teeth, the patient must be sufficient bone to house the implant. However, patients who are in greatest need for an implant for fixation of their dental prostheses are often lacking in bone. This is because of the natural shrinkage of jaw bone after a tooth has been lost. If a removable denture is used as a replacement for several years, the pressure from the denture would have caused even more resorption. As more resorption takes place, the denture becomes unstable and implants become necessary for additional retention of the denture. For this group of patients, additional procedures to augment the bone may be needed prior to implant placement. These pre-implant surgeries are needed not only for functional reasons but for aesthetic purposes as well.
- Bone augmentation
The most commonly used technique is bone grafting. This is basically a “robbing Peter to pay Paul” approach. Bone is taken from another part of the body, eg the hip bone (iliac crest), leg bone (tibia), chin bone, etc, and added to the implant site. Using the patient’s own (autogenous) bone for grafting is the gold standard. However, it involves a donor site surgery which has its own morbidity. As such, there is a demand for an alternative source of bone graft. There are tissue banks that process human and animal bone, sterilize them and pack them into bottles. There are also purely synthetic bone substitutes available. For a limited area of bone grafting, these alternatives do work pretty well. However, for large volumes, I prefer to use autogenous bone for more better results.
Adding bone volume – distraction osteogenesis
When the vertical dimension of the jaw bone is lacking, augmentation is best done by distraction osteogenesis. This is a procedure whereby a section of bone is cut and attached to a device and moved gradually on a daily basis to “stretch” the bone. As the segment is moved away from its base, it will lay down new bone. This bone is then left to undergo mineralization for a couple of months before it is solid enough to have an implant inserted.
2. Enhancing the quality of the graft
Bone graft healing can also be enhanced by mixing it with platelet-rich plasma (PRP) or bone marrow aspirate concentrate (BMAC). PRP is prepared by centrifuging some of the patient’s own blood to separate out the platelet components into a small volume. Platelets contain a high concentration of growth factors which can then be mixed with the bone graft to enhance the healing process. BMAC uses a similar technology but instead of centrifuging blood, bone marrow aspirated from the hip bone is concentrated into a small volume to be grafted into the area for bone is needed.
Techniques of grafting
- Onlay Bone Grafting
There are many ways that the bone graft can be placed onto the recipient sites. One of the most common technique is the onlay bone graft whereby whereby the a block of bone is screwed onto the recipient site. Over a period of several months, the graft will integrate with the recipient site and the implant can be placed.Particulate bone graft
However, block bone tends to resorb more over time due to poor penetration of the bone by new blood vessels. To enhance better revascularization, the bone graft can be grounded into particulate form and adapted onto the recipient site. In this form, a “container” such as a titanium mesh or collagen membrane is needed to cover the graft particles to confine it to the recipient site.
- Inlay Bone Grafting
This technique involves placing bone above the jaw bone, away from the surface of the bone where the implant is to be placed. This method is exclusively available in the upper jaw only where there are empty spaces such as the sinuses and the nasal cavities which can be filled with bone.Sinus floor grafting
In the back of the upper jaw, bone is often deficient after extraction. Augmentation can be done by lifting up the sinus lining and placing the bone graft between the sinus lining and the bony floor of the sinus. This way, vertical height of the bone available for implants can be increased.Nasal floor grafting
In the front of the upper jaw, augmentation of the height of bone available for dental implants can be done in a similar fashion but lifting up the nasal lining and placing the bone graft between the nasal lining and the bony floor of the nose.
- “Sandwich” bone graft
Jaw bone volume can also be augmented by splitting the bone open and placing bone graft in between the two split ends. This method of “sandwiching” bone graft between the bone has the best results but it is contingent on the jaw bone dimensions being big enough to be split in the first place. By sandwiching the bone graft between two ends of the bone, revascularization of the graft is most efficiently done.
There are many techniques and materials available for augmentation of the jaw bone to render it suitable for dental implants. While additional procedures may seem to complicate the treatment, many of these procedures can be done at the same time as the implant surgery.