Background: When one thinks of improving the shape of the lower jaw it is important to consider what exact dimensional changes are needed at its corners to achieve the desired effect. What are the 3D changes that are needed at the chin and jaw angles? Once this is known then the correct surgery can be applied that has the best chance to achieve the overall desired jaw shape change.
This is no better illustrated that in the patient who presents for aesthetic jaw augmentation with a steep mandibular plane angle. By definition a steep mandibular plane angle means that the L shape of the jaw is under rotated by virtue of the lack of ramus development. (the vertical limb of the L) This results in visibly high jaw angles and a chin is horizontally short. In some cases with good development of the body of the mandible (the horizontal limb of the L) the chin projection is inadequate but the chin is vertically long. (not because it really developed with too much height but because the jaw is angled downward) This is also why the face looks vertically long and narrow.
In treating this type of steep mandibular angle jaw shape the key dimensional changes are to bring the chin forward as well as shortening it and lowering the jaw angles and widening them as well. To do so requires a combination of bone movement and implant augmentation.
Case Study: This male has a very steep mandibular plane angle with high narrow jaw angles and a short but long chin. In addition to his steep plane angle he had some jaw asymmetry as well.
In order to derotate his steep mandibular plane angle, the surgical plan consisted of a sliding genioplasty with a horizontal movement of 12mms and an upward movement (shortening) of 4mms. The rest of the jawline was treated by vertical lengthening of the jaw angles with an implant that extended to the repositioned chin bone. In the design it wrapped around the advanced chin bone like a complete around jawline implant…but that is only done so in surgery there is enough jaw implant length to cross adequately onto the chin bone and be able to be secured with screws. It is not necessarily designed to create a true wraparound effect across the chin.
During surgery an intraoral bony osteotomy was performed which advanced his chin 12mms and vertically shortened it by 4mms. The extended jaw implant was cut into two pieces in the midline and placed through posterior vestibular incisions on each side. Their anterior ends passed underneath the mental nerves and onto the chin area where they were secured with a screw on each side.
This combined bony genioplasty-implant approach to the steep mandibular plane angle is the most effective approach to creating the needed 3D changes for a more proportionate lower facial shape. One of the key steps is to be able to pass the implant beneath the mental. nerve where the back end of the osteotomy cuts reside. This does require some stretching of the nerve if it has a low position on the bone…which this patient had. This will result in some numbness of the nerve’s distribution but as long as the nerve is intact it should eventually recover.
Case Highlights:
1) The steep mandibular plane angle lower facial patients has a short but long chin and high and narrow jaw angles.
2) Derotating the steep mandibular angle through chin advancement and shortening with lengthening the jaw angles is the key to a successful jaw augmentation which shortens the long face.
3) A custom jawline implant alone is not adequate due to the need for considerable horizontal advancement and vertical SHORTENING of the chin. Only a sliding genioplasty can make this dimensional change.
Dr. Barry Eppley
World Renowned Plastic Surgeon