Abstract
Patients with poor skeletal foundations, as seen with microgenia, will not only tend to show certain stigmata of aging earlier, such as poor necklines and jowling, but will also obtain less than ideal results from a facelift. In the appropriate patients, correction of microgenia is a critical technique for facial rejuvenation, either as a stand-alone procedure or in conjunction with facelifting.
Keywords
Mentoplasty, Submental incision, Microgenia, Retrogenia
History
Chin augmentation has been performed using autografts, alloplastic materials, and mandibular advancement procedures. Autografts are complicated by the need for a donor site, difficulty with shaping the grafts, and their unpredictable pattern of resorption . In contrast, alloplastic implants have proved to be an easy and reliable means of augmentation. The most common method of augmentation is with alloplastic implants, including Silastic, Gore-Tex, Mersilene mesh, and Medpore implants . Silastic chin implants have the longest history of continuous use of any of the alloplastic implants. They have been safely used since the 1960s with a high degree of satisfaction. Mandibular advancement procedures require specialized equipment and add significant morbidity to the procedure with little advantage.
The most significant evolution in mentoplasty has been in implant design. The earliest Silastic implants were carved individually by the surgeon. In 1966 Safian and Dow Corning introduced the first preformed Silastic implants . These implants were equivalent to what is now referred to as a curvilinear implant or a central implant without a lateral component. Augmentation was isolated to the central mentum and provided only anterior projection. The next important advancement in implant design was the introduction of the anatomic style of implant by Toranto in 1982 . These types of implants have lateral tapering extensions, which wrap around the mandible, providing anterior projection of the mentum, filling of the prejowl sulcus, and an overall recontouring of the mandible. The result is a more natural augmentation of the chin–jawline complex. These implants are available as either anatomical chin implants (Spectrum Designs Medical, Carpinteria, CA, USA) or extended anatomical chin implants (Implantech, Ventura, CA, USA). Realizing the importance of isolated prejowl augmentation in certain patients, Mittleman introduced his prejowl implant, which has a thin central portion and provides bulk only in the lateral arms .
The surgical technique for mentoplasty using alloplastic implants has not significantly changed in recent years. The two common surgical approaches are an external technique through a submental incision and an intraoral technique through a gingivolabial sulcus incision. Both approaches are commonly used today, generally determined by the preference of the individual surgeon.
Personal Philosophy
An optimal facial skeletal structure serves as the foundation for rhytidectomy and other facial rejuvenation procedures. Patients with poor skeletal foundations, as seen with microgenia, will not only tend to show certain stigmata of aging earlier, such as poor necklines and jowling, but will also obtain less than ideal results from a facelift. In the appropriate patients, correction of microgenia is a critical technique for facial rejuvenation, either as a stand-alone procedure or in conjunction with facelifting ( Fig. 22.1 ).
Alloplastic implantation provides a safe, reliable, and relatively simple means for chin augmentation. Ideally the implant should have a very low incidence of infection or rejection, provide predictable long-term results, and be easy to remove if necessary. Silastic, a nonporous material around which a fibrous capsule forms, meets all of these criteria .
Our preferred implants are the extended anatomic (Implantech), or anatomical (Spectrum Medical), implants; for the purpose of this chapter we will be referring to both as “anatomical chin implants.” These implants fill the central mentum and have lateral arms that fill the prejowl sulcus to produce a natural jawline. The lateral arms on these implants also account for the lower incidence of implant shifting relative to the central style implants. The anatomical style implants are available from each manufacturer in four sizes, providing between 5 and 9 mm of anterior projection. As the implant size increases, so does the length and bulk of the implant’s lateral arms.
Central implants do not have a lateral extension to fill the prejowl sulcus. In patients with preexisting jowls, the central implant will accentuate the prejowl sulcus, often making the jowl appear more prominent. This is the opposite effect of the extended anatomical chin implant, which, by filling the prejowl sulcus, will reduce or camouflage the appearance of a jowl. In younger patients without jowls, central implants also have the negative effect of creating a more pointed appearing chin.
When performing mentoplasty we routinely have a 2-mm Silastic extension wafer available . The wafer provides a degree of intraoperative flexibility in terms of implant sizing. On intraoperative assessment, if the patient would benefit from further anterior projection, a wafer can be placed under the central portion of the chin implant, increasing anterior central mentum projection by 2 mm.
We perform all mentoplasties through a submental incision. The submental incision hides well and facilitates accurate implant placement, particularly for anatomical chin implants, which require a lateral subperiosteal pocket along the anterior-inferior mandibular border. The submental approach also allows for suture fixation of the implant to the mandibular periosteum, thereby preventing implant shifting and vertical migration. Implants placed through an intraoral approach are exposed to oral contaminants and have a greater likelihood for infection.
Anatomy
The chin is composed of the overlying skin, subcutaneous fat, muscles, and the mandible. The muscle components of the chin are the mentalis, depressor labii inferioris, and depressor anguli oris muscles, all of which are innervated by the marginal mandibular branch of the facial nerve. The mentalis muscle arises from the incisive fossa on the mandible and inserts inferiorly into the dermis of the chin. The mentalis muscle elevates the chin pad. The depressor labii inferioris and depressor anguli oris muscles arise from the oblique line of the mandible and insert into the lip. Together they act to depress the lower lip and corners of the mouth, respectively.
The portions of the mandible relevant to mentoplasty are the symphysis, parasymphysis, and the body of the mandible. The mental nerve exits the mental foramen, and provides sensation to the chin and lower lip. The mental foramen is generally found inferior to the second premolar . The mental foramen is approximately 2.5 cm lateral to the midline, and is located 1 cm above the inferior border of the mandible. The foramen can also been found at a point midway between the alveolar ridge superiorly and the inferior edge of the mandible.
The anatomy of the chin-jawline complex changes with age. Soft tissue and bone atrophy in the central mentum can lead to, or exaggerate, the appearance of a receding chin. Development or exaggeration of a prejowl sulcus is also caused by atrophy of soft tissue and bone. Age-related atrophy of the anterior mandibular groove, located inferior to the mental foramen, contributes to the prejowl sulcus . Jowl formation, which exaggerates the depth of the prejowl sulcus, results from ptosis of skin, muscle, and subcutaneous fat.
Preoperative Assessment
Deficiencies of the chin are important to assess for both the older patient seeking facial rejuvenation and the younger patient desiring an improved facial appearance. A receding chin produces an imbalance of the lower third of the face and can be corrected with a chin implant. Increasing chin projection will also improve the patient’s appearance on front view, where a weak lower third can give a rounded, less angular facial appearance.
The most common abnormality of the chin is microgenia (retrogenia), which refers to an underprojection of the chin with normal occlusion. Patients with a receding chin have a short hyoid-to-mentum distance, often associated with an obtuse cervicomental angle. Chin augmentation increases the distance from hyoid to mentum, providing the appearance of a more acute cervicomental angle ( Fig. 22.2 ). In younger patients with submental fullness and good skin tone, the addition of submental liposuction can significantly enhance the result of chin implantation ( Fig. 22.3 ).
The simplest and most practical means to determine appropriate chin projection on profile is by dropping a line down from the lower vermilion, perpendicular to the Frankfurt horizontal. Ideally, the pogonion (the anterior most projection of the chin) should approach this line. Patients whose projection falls behind this line should be considered for augmentation mentoplasty. Patients should also be evaluated while smiling, as smiling may increase projection to a degree that may influence the choice of implant. The ideal anterior projection is gender specific. In women, several millimeters of underprojection is acceptable, whereas men can tolerate slight overprojection, providing a stronger chin. Malocclusions should be noted and, if present, referred for orthognathic evaluation.
Development of a prejowl sulcus is a characteristic sign of aging. In a patient with minimal jowl, filling the prejowl sulcus with an implant may give a jawline comparable to that achieved with a facelift. In patients with a greater degree of jowling, isolated prejowl sulcus augmentation will be inadequate; in these patients a facelift is needed to get the optimal jawline rejuvenation. Before rhytidectomy for correction of the jowl, it is important to evaluate the depth of the prejowl sulcus to determine if it will be completely effaced by a facelift. In the setting of more advanced prejowl sulcus volume loss, a rhytidectomy alone may fail to produce the desired jawline. These patients should be considered for prejowl sulcus augmentation with or without central mentum projection, depending on their chin projection on profile.
Analysis of a patient with a receding and aged chin may reveal volume deficiencies outside of the areas adequately addressed with an implant. Chin implant placement, and therefore its area of augmentation, is limited superiorly by the mental nerve. Individuals with thin faces and more significant microgenia commonly have a deep labiomental sulcus. If ignored at the time of surgery, isolated placement of an alloplastic chin implant may exaggerate the depth of the labiomental sulcus. Proper identification and treatment of this deficiency will optimize both the aesthetic result and the patient’s satisfaction. Autologous fat transfer can be performed concurrently with mentoplasty to help soften the sulcus. Alternatively, injectable fillers can be used postoperatively to address this deficit ( Fig. 22.4 ).
