Background: The shape of the lower face is affected by the posteriorly paired jaw angle bones. The jaw angles are three-dimensional structures which have length, width and a shape influenced by the posterior projection of the intersection of its posterior and inferior borders. While located in the back part of the lower face the symmetry of the jaw angles is easily seen and scrutinized.
While many people do not have naturally good symmetry between the jaw angles, certain procedures can create asymmetry on their own. The most common surgical procedure performed on the jaw angles is the sagittal split ramus osteotomy. (SSRO) Splitting the thickness of the bone sagittally allows the teeth-containing distal segment to be moved forward or back, putting the split ramal segments back albeit with an altered shape. Between these bone shape changes, how these partially devascularized bone segments heal and that there are two sides, it is not rare that bony jaw angle asymmetry can result.
Since the SSRO can not produce any jaw angle width, secondary aesthetic augmentation using jaw angle implants may be desired. The use of standard jaw angle implants may be effective but further asymmetry is always a high risk. Between two different bony sides and the variables that come with jaw angle implant placement, it can be hard to avoid noticeable asymmetry afterwards.
Case Study: This male had a history of bimaxillary orthognsthic surgery with a sliding genioplasty. Because of his naturally narrow face he had standard widening jaw angle implants placed by another surgeon. While he ended up pleased with the left side, the right side was more narrow and asymmetric. A 3D CT scan showed the differences between the jaw angle bone shape and positioning of the jaw angle implants.
From the 3D CT scan a custom right jaw angle implant was designed to match the width and shape of the augmented left jaw angle/jawline side. It is interesting that just looking at the computer matched right side to the left side how it looks too big or excessive in width and length.
The differences in size and shape of the standard vs custom right jaw angle implants could be best appreciated during the removal and replacement surgery.
This case illustrates the difficulties in jaw angle implant surgery when bony asymmetry exists. Even small amounts of asymmetry can result in enhanced asymmetries when magnified by implant augmentation. It also illustrates how inaccurate the human eye is when trying to place paired implants that have two completely different pockets located in the deep recesses of the mouth. While using a computer implant design process does not guarantee absolute jaw angle symmetry, it gives one the best chance to limit how much asymmetry could occur and get the best outcome possible.
1) Sagittal split osteotomes (SSRO) of the mandibular rami can create bony jaw angle asymmetry.
2) Standard jaw angle implants may help secondarily to improve jaw angle shape but symmetry can be hard to achieve.
3) A custom jaw angle implant design provides the best change for bilateral posterior lower facial augmentation symmetry.
Dr. Barry Eppley