One of the important and/or desired aesthetic features of the male face is a strong lower jawline. The three corners of the jawline, the chin and paired jaw angles, are the major components of it. Much has been written about the desired anatomic features of the chin but much less so about that of the jaw angles.
The desired external features of the jaw angle have been described but how to achieve them from implant designs has not really been investigated much at all. While standard styles of jaw angle implants have been around for over twenty five years, their designs comes from basic shapes using regular skeletal jaw models.
When undertaking custom jawline implants one has the opportunity to not only make an implant with a specific fit to the patient’s bone but it can also have any number of shapes. The key question is what should those jaw angle shapes be? What is the specific shape of a good looking jaw angle? It is common to perceive that a defined jaw angle shape is on that is square and sharply angular…but is this so?
I have had the opportunity to do many custom facial implants which require 3D CT scans. Looking at these scans one can observe many features of the bony anatomy of the facial bones that is not visible in plain x-rays or even in any anatomy texts. In looking at male patients that have well defined jaw angles externally (they were getting custom implants for other parts of the face), the bony features of a well defined jaw angles become more clear. My observations are as follows.
First no well defined jaw angle has a square bony shape. Every corner of the jaw angle, which represents the intersection of the posterior and inferior borders is round. While the intersection of these two border lines can be in the range of 100 to 110 degrees the actual corner is round. The level of the jaw angle to the chin, even in the ‘squarest’ of jaw angles, is still well above that of the chin. (in the 15 to 25 degree range)
These two bony shapes of a good jaw angle are fairly well known. But what is not appreciated is the shape of the bone above the angle. Most of the ramus has a bony recess into which the bulk of the masseter muscle resides. In essence the bony rim of the jaw angle is raised but the bulk of the bony jaw angle above it is a concavity. This bony concavity allows the greatest thickness of the muscle to sit within it. At the peripheral insertions of the masseter muscle (rim level) the muscle is the thinnest. Unlike what is depicted in may jaw models the angle region is not a smooth even surface. This indicates that the more the jaw angle bone is developed the larger the masseter muscle is that needs to move (pull) on it.
Another rarely mentioned feature of the bony jaw angle is the prominent knobs of bone seen along the inferior border.These raised bony knobs serve as musculoligamentous attachments which can occur as a solitary knob but often appears in two or three raised bony prominences. These are not really important for aesthetic designs but have relevance for implant placement. The larger in size and number of these knobs that are present indicates the adherent nature of the musculoligamentous attachments and are markers for the subperiosteal dissection. They can also be used engagement points for the implant and can aid in implant placement.
Interestingly on the internal surface of the bony jaw angle these muscle ligamentous attachments points are located more on the posterior border rather than the inferior border. This is consistent with the location of the insertion of the medial pterygoid muscle.
One bone shape feature of the well defined jaw angle is the near or complete absence of an antegonial notch. The antegonial notch is the concavity of the undersurface of the inferior border just anterior to the angle. It is present due to the influence of the elevator and depressor muscles on the bone. Its presence, particularly when it is pronounced, is often indicative of a lower jaw that is less well developed with a more vertical growth pattern. (as opposed to horizontal growth)
The well defined jaw angle (the term square should he eliminated as descriptive for this area) has a round angle shape with intersecting posterior and inferior border lines of 100 to 110 degrees. The bony rim around the inferoposterior border is raised with which a concave recess occupying most of the internal bone surface. An antegonial notch is not present. Such if not all of these bony features should be considered in custom jaw angle and jawline implant designs.
Dr. Barry Eppley
Indianapolis, Indiana