Bringing the entire lower jaw forward to correct a malocclusion has been by the sagittal split ramps osteotomy (SSRO) for over fifty years. While a commonly performed procedure that is often taken for granted due to its universal use, it is one of the most clever facial osteotomies every designed. In an effort to move the lower jaw forward but not leave a open gap from a full-thickness transverse bone cut behind the teeth in the mandibular ramus, the split-thickness bone split method was developed.
As the name implies, the SSRO separates the ramus of the mandible in a longitudinal fashion. This creates a proximal (outer) segment that contains the condyle and a distal (inner) segment which has all the teeth and chin attached. As the inner distal segment slides out to get the lower teeth in better alignment with the upper teeth, good bone contact is maintained between the proximal and distal bone segments which are the secured with a plate and screws.
While a tremendously successful orthognathic surgery procedure the SSRO is not without its potential complications. Such complications are well known and include inferior alveolar nerve injury and the risk of incomplete or non-healing of the two segments. But beyond these medical complications, the SSRO also has an aesthetic complication as well which is that of loss of the jaw angle prominence. Due to proximal segment rotation during positioning or bone resorption due to partial avascular necrosis, some SSRO patients will develop partial or complete loss of their jaw angle prominence. This may also occur as the jaw movement forward and the resultant increased chin prominence creates a pseudo jaw angle deficiency by comparison.
Restoration or reconstruction of lost jaw angles is done best by the use of custom jaw angle implants made from a 3D CT scan. This is particularly needed as the the jaw angles after an SSRO are often asymmetrical and even more so if they were before surgery. The amount of bone shape change at the angles is never symmetric. Given that some portion of the implant will be off the bone, which is what creates the new jaw angle shape, a good fit to the bone is important.
One advantage of a prior SSRO procedure in designing custom jaw angle implants is that the indwelling hardware can be used an intraoperative reference. The implant can be designed right up against the plate or screw heads. This provides a visual reference in surgery for proper positioning of the imply through the limited visibility that exists at an incision way back inside the mouth.
Dr. Barry Eppley
Indianapolis, Indiana