Background: Aesthetic evaluation of the lower third of the face is historically based on the concepts of the facial thirds. This is a frontal view concept evaluating the vertical relationship/ratios of the upper, middle and lower facial thirds. This linear measurement can detect a short lower third of the face which is aesthetically treated by vertical chin lengthening.
But when it comes to the side or profile view of the face, the facial thirds concept fails to be useful. This is because in side profile the lower third of the face is at an angle and what works back at the jaw angle does not work for the chin. This change in vertical heights is known as the mandibular plane angle. While it is traditionally an orthodontic and cephalometric measurement, it has value as an aesthetic concept in jawline augmentation. This is because using custom jawline implants, who are connected between the chin and the jaw angles, can effectively change the tilt of the mandibular plane angle by its design.
In the high mandibular plane angle patient, vertical jaw angle lengthening is needed and the chin either stays the same or is vertically shortened. Conversely in the low or near flat mandibular plane angle patient, the chin must be vertically lengthened as the jaw angle can not be vertically shortened
Case Study: This young male presented for jawline augmentation. He had a vertically short lower third of his face by examination that was most pronounced in the chin. He also had a moderate horizontal chin deficiency. His 3D CT scan showed a flatter mandibular plane angle shape of around 20 degrees. A custom jawline implant was designed that provided a horizontal chin increase of 7mm and a vertical lengthening of 4mms. The he jaw angles were only widened with no vertical lengthening. Given his more narrow facial type a non-linear design was done in the frontal view between the chin and the jaw angles. A square chin shape was made at 35mms.
Under general anesthesia and through a small submental skin incision and two intraoral incisions, the custom jawline implant was placed as a single piece. The chin was secured with two screws to keep it horizontally level which allows the jaw angle portion of the implant to be set into position and secured by additional screws. The impact of the square chin design could be appreciated immediately once the chin part of the implant was labeled and secured into place.
Evaluation of the external appearance of the mandibular plane angle has a useful role in how to design custom jawline implants. While it is but one factor in their design, it provides an important guide to the profile appearance on the lower third of the face.
1) The low mandibular plane angle patient needs an aesthetic rotation of the jawline. jawline augmentation that vertically lengthens the chin and widens the jaw angles.
2) Aesthetic rotation of the jawline to increase the mandibular plane angle requires vertical lengthening of the chin and widening of the jaw angles.
3) A preoperatively designed custom jawline implant allows for the most effective change in the mandibular plane angle.
Dr. Barry Eppley