The antegonial notch is a well known feature of the lower jaw. It occurs as a concavity or elevation of the inferior border in front of the jaw or gonial angle. Because of this location it has also been called the pregonial notch. It does not appear in everyone and it is more common in men than women. Its origin has been studied and postulated for decades in relation to what it means for the growth and development of the mandible.
The antegonial notch has been associated with certain types of facial growth patterns. It is prominently seen in numerous types of congenital growth deformities of the lower jaw and, as a result, it has been associated with underdevelopment of the bone. While it may be seen with larger concavities in these conditions it exists in lesser degrees in people with normal mandibular development and occlusions.
Regardless of why the antegonial notch is present, it is commonly seen in many patients who are undergoing custom jaw angle and jawline implants. As these patients all receive 3D CT scans the opportunity to appreciate lower jaw anatomy is unparalleled. In these 3D CT scans it can be seen that the majority of people have an antegonial notch to some degree. It is definitely more prominent in high mandibular plane angle patients and much less so the lower the plane angle becomes.
But what is aesthetically relevant is how does the antegonial notch factor into custom jawline implant designs? As a general rule most jawline implant designs strive to eliminate the antegonial notch and create a smooth linear line from the jaw angles to the chin. This can be done with or without any lowering (vertical lengthening) of the jaw angles.
In the high mandibular plane angle patient where significant lowering of the jaw angles needs to be done the antegonial notch is naturally eliminated as part of the design. But in some of these patients the amount of vertical jaw angle lengthening may need to be less than ideal to eliminate the antegonial notch for fear of the masseter muscle not adequately covering the entire jaw angle implant region.
There are some design scenarios where a patient may prefer to keep some semblance of the antegonial notch to create a non-linear jawline design. This raises the question as to what is the best aesthetic role of the antegonial notch if any? It is my observation that in men that have naturally good jaw angle prominences but have a non-linear jawline shape, it is because they have a prominent antegonial notch.This is because the jawline to go inward in front of the masseter muscle prominence, creating a distinct flare to the jaw angles from the front view.
One ‘advantage’ of having an antegonial notch is it can be eliminated without lowering of the jaw angle…which lessens the risk of postoperative masseteric muscle dehiscence. When the antegonial notch does not exist and the jaw angle is high and rounded lowering the jaw angle, which is usually necessary, raises the risk of inadequate muscle coverage over the angle of the implant.
Dr. Barry Eppley