Background: The shape of the jawline consists of various anatomic zones that has numerous dimensions. While the most common aesthetic concerns are a chin that does not have enough horizontal projection or jaw angles that are not wide enough, there are many other types of aesthetic deformities of the jawline.
One such undesired jawline shape is that of the ‘high angle jaw deformity’. This is a jawline shape that has high vertically short jaw angles at the back end and a vertically long chin on the front end. The resultant slope of the jawline creates a high mandibular plane angle. The mandibular plane angle is traditionally described by cephalometrics as the angle formed by the intersection of the Frankfort horizontal line with a line drawn through the mandibular plane. (Frankfurt Mandibular Plane Angle or FMPA) The normal range for the mandibular plane angle is around 22 degrees +/- 5 degrees.
Short of doing an x-ray analysis, the alternative way is to measure the interaction of the mandibular plane line with that of horizontal line drawn for the lowest chin point back. This will roughly create a similar angle number as that of the FMPA.
The high angle jaw deformity creates a hyperdivergent face where the chin can look and actually be long, the back of the jaw looks deficient/missing and the face can seem long and narrow. Creating an improved lower facial shape requires elongating the jaw angles and shortening the chin.
Case Study: This young female was bothered by the shape of her jaw, feeling that her chin was long and her jaw angles too high. This gave her a steep mandibular plane angle and a long thin face.
The concept for her aesthetic jaw surgery was to elongate the jaw angles with implants and vertically reduce the chin bone.
Under general anesthesia an intraoral approach was used to perform a wedge reduction bony genioplasty. A 5mm wedge of bone was removed and the downfractured chin segment put back together with small plates and screws. Through intraoral posterior vestibular incisions custom jaw angle implants were placed that lowered the jaw angles by 10mms (5mm width) and had long anterior wings that came forward to the back of the bony genioplasty cut.
Short of orthognathic surgery correction of a high angle jaw deformity requires alteration of the front and back ends of the bony jaw. While bone removal can vertically shorten the chin, custom designed implants are needed to drop the jaw angles down.
Highlights:
1) A high jaw angle can be associated with a vertically long chin.
2) Reshaping the high mandibular plane angle jaw consists of vertically lengthening the jaw angles and vertically shortening the chin.
3) Custom jaw angle implants are needed to create the smoothest jawline that joins with the reduced chin.
Dr. Barry Eppley
Indianapolis, Indiana