An autogenous onlay graft procedure always requires a donor site, from which the graft bone is taken. In the oral cavity this is mostly the back of the the lower jaw, right about where the third molars or wisdom teeth are, or the chin. The chin has always been preferred due to its exceptional bone quality, however, the harvesting process is a little more involved as compared to the back of the jaw.
It is often a good idea to have the final surgical template for the implants also ready for the grafting procedure. To the left we can see what the discrepancy actually really is and how "thick" of a graft piece we need to harvest, in order to satisfy our width requirements for later implant placement. Here, the clinical ridge dimensions match those of the axial CT scan shown above.
Once we know our graft thickness, we can go ahead and expose the donor site area. Today I would actually take the extra step and make the initial incision around the incisor teeth, rather than at the mucosal level. It is important to reflect far enough inferiorly, so that the "safety space" to the apices of the teeth is not violated. With a mucosal incision we are forced to re-suture the mentalis muscle properly on closure, so that the soft tissues don't "sag" around the chin after the procedure.
The pre-measured graft blocks are outlined (we use piezoelectric handpieces for this nowadays), and the fixation screws are already inserted into the graft pieces. This has the added advantage, that the graft will usually break loose at the depth at which the fixation screws are inserted. This of course, along with the measured depth outline will assure a block of bone graft with a fairly even thickness.
The graft pieces are then trimmed as necessary and attached to the deficient ridge. The template is tried in again in order to assure that sufficient width has been obtained. It is usually recommended to "overbuild" the volume by approximately 10%, due to some inevitable resorption during the integration process. Once fixated, both, the donor and recipient sites are closed up and the graft is left in place for 4 - 6 months.
Six months later, we can see on the left image that we have come very close to the desired ridge width. Some shrinkage has obviously taken place, but not to the point where it puts our implant placement in jeopardy. The internal, concave areas of the template is our guide for the external convex surfaces of the implants, in order to eventually "line up" the buccal surfaces of the natural teeth and implant teeth properly, given that that is what the occlusal scheme can support, of course.
When the site is re-accessed, one can see the dramatic difference in alveolar ridge with we know have, as is shown on the image to the left. The interface between the donor and recipient bone is barely visible and the graft is perfectly stable. All of the fixation screws are removed and the osteotomies are prepared for the five planned implants.
We were able to place five dental implants of proper diameter into the grafted area. These implants would then remain submerged for another six months under the gum tissues to fully integrate, until we were finally able to uncover them and build the final prosthesis for the patient.
This patient is now running about 12 years post-op and the implants are in excellent condition.
