Chin augmentation is a popular cosmetic procedure that can produce dramatic, aesthetically pleasing results in appropriately selected patients. This technically straightforward procedure has a relatively low incidence of complications and can be a useful adjunct in a number of situations. This article will describe patient selection, mandibular anatomy, surgical technique, and possible complications related to mandibular alloplastic implantation
Chin augmentation and mandibular contouring are essential procedures in addressing the ageing or hypoplastic mandible, and ensuring optimal results in both facial rejuvenation and beautification surgery. These procedures have become increasingly popular owing to a better understanding of the anatomy and ageing process of the mandible. Currently, the implants used in mandibular augmentation are well designed, both artistically and anatomically, and able to provide significant cosmetic improvement with a relatively uncomplicated procedure that is completely reversible. Few other procedures in the surgeon’s repertoire yield as much benefit for as little time and effort as mandibular augmentation with the appropriately chosen alloplastic implant.
As with all patients pursuing cosmetic surgery, each patient’s motivation and emotional state should be assessed to ensure they are appropriate for surgery. A complete medical history should then be accounted for with specific attention to clotting disorders, anaesthetic risk factors, osteoporosis, prior trauma, congenital abnormalities, dental/orthognathic history, prior cancers, and radiation treatment. The surgeon should also ask the patient about prior surgical and cosmetic procedures, including injectable fillers. It is very important to evaluate and identify any signs of functional mandibular problems such as malocclusion and temporomandibular joint dysfunction; these issues are not addressed by mandibular augmentation surgery, and should prompt a referral to the appropriate specialist for further evaluation.
The mental nerve, which supplies sensation to the lower lip and chin, travels through the mandible until exiting in a superior direction at the mental foramen. The mental nerve is usually located immediately inferior to the second mandibular premolar on each side, but can be slightly more anterior or posterior in up to 50% of patients1. In the typical young adult mandible, the mental foramen is located approximately halfway between the alveolar ridge and the inferior border of the mandible (Figure 1), and approximately 25 mm lateral to the midline, with a range of 20 to 30 mm2. In children, the mental foramen lies closer to the inferior border of the mandible, and slightly more anterior. During the ageing process, atrophy of the alveolar ridge causes the foramen to lie in a relatively more superior position while the distance to the inferior border of the mandible remains fairly constant. Generally, there is a distance of at least 8–10 mm and on average, 15 mm between the mental foramen and the inferior border of the mandible3.
Although the development of a hypoplastic mentum is largely determined by genetic factors, the development of a prejowl sulcus is primarily the result of ageing. However, occasionally the prejowl sulcus may be present from childhood. Relating to the bony mandible, gradual bony resorption of the inferior mandibular edge between the chin and the remainder of the body of the mandible (the inferior extension of the ‘marionette line’) results in the development of the anterior mandibular groove, as named by the senior author. The combination of this bony resorption and progressive soft tissue atrophy during ageing results in the development of the prejowl sulcus (Figure 2)4,5. With continued ageing, the prejowl sulcus may merge with the commissure–mandibular groove, or ‘marionette’.
Aesthetic and functional analysis
Facial aesthetic analysis, as summarised by Powell and Humphreys6, includes both a frontal and a lateral assessment. On frontal view, the face is divided into thirds, with the lower third extending from the subnasale to the menton. The lower third can be further subdivided into thirds such that the upper third is located from the subnasale to the stomion superiorus and the lower two thirds is located from the stomion inferiorus to the menton. There is loss of the vertical height and anterior projection of the mandible with advancing age, resulting in a loss of ideal proportions. In addition, the soft tissues covering the mandible often display some atrophy as well. On lateral view, Gonzales-Ulloa7 defined ideal chin projection at a line dropped from the nasion perpendicular to the Frankfort horizontal plane. Another method defines ideal chin projection at a line dropped from the vermilion border of the lower lip perpendicular to the Frankfort horizontal plane. While a man’s ideal pogonion position is tangential to this line, a woman’s ideal pogonion position may lie 1–2 mm posterior to it. In the presence of normal, class I occlusion, a hypoplastic mentum is defined as chin projection posterior to this line in a man, or more than 1–2 mm posterior to this line in a woman.
Perhaps most importantly, the examiner should evaluate for any functional disturbance of the mandible, such as malocclusion or temporomandibular joint dysfunction. The overlying soft tissue should also be evaluated and any pathology noted. Patients with a severely hypoplastic mentum and strong mentalis leading to lip incompetence should be considered for osseous advancement.
The main indication for chin augmentation is a mild to moderately hypoplastic mentum. As described above, there are a number of different methods to describe the appropriate relationship of chin position to the rest of the face. The senior author prefers to use a straight line perpendicular to the Frankfort horizontal dropped from the vermillion to estimate appropriate anterior projection.
The presence of a prejowl sulcus is an indication for prejowl augmentation. While deficiency of volume in the prejowl area may be related to bony deficiency or to soft tissue deficiency alone, it is often both. Mild soft tissue deficiency in the prejowl area may at times be corrected with filler injection alone.