CHAPTER 35 Autologous contouring the lower face
Surgery on the lower-third of the face may be performed to reconstruct congenital or acquired deficits or to enhance facial aesthetics. These goals can be accomplished by any combination of bony osteotomies or ostectomies, alloplastic augmentation, skin resurfacing or redraping, and/or soft tissue fill. While soft tissue operations of the face are described elsewhere in this text and orthognathic movements of the midface and mandible are beyond the scope of this chapter, we will highlight autologous genioplasty. Obwegeser provided the first detailed description of bony chin surgery in 1957. The osseous genioplasty, however, was not popularized until 1964 when Converse reported the horizontal osteotomy of the mandible to reposition the genial segment. Since then, chin surgery has become a common aesthetic procedure that can complement other procedures such as rhinoplasty, rhytidectomy, or platysmaplasty.
Although improvements in alloplastic materials developed in the 1970s and 1980s have led many surgeons to choose alloplastic chin augmentation, the osseous genioplasty should not be overlooked. The osseous genioplasty remains a versatile operation that can address a wide variety of chin deformities ranging from microgenia to macrogenia to chin asymmetry. Moreover, osseous genioplasty avoids alloplastic materials and the attendant complications that can occur with a long-term foreign body in situ. This chapter will detail the technical aspects of osseous genioplasty.
While the neoclassical artistic paradigm recommends that the lower-third of the face be divided into equal thirds – the upper lip, the lower lip, and the chin – such rules are only of limited utility in surgical planning. One of the principal errors a surgeon can make in assessing the lower-third of the face is to limit evaluation to the chin only – particularly the bony component of the chin. Rather, not only must the aesthetics of the chin be balanced in relation to the facial structure, but it is necessary to take into consideration the stature and sex of the patient as well. When evaluating the chin, a systematic approach to the physical examination is helpful. For example, when honing in on the lower third of the face, a step-by-step evaluation from nose to chin should include the lower midface, nasolabial folds, upper and lower lip relationship, incisor tooth show, labiomandibular fold, lower lip eversion and inclination, height and depth of the labiomental fold, chin pad thickness, static soft tissue ptosis, and dynamic chin pad motion with smile.
Large-format frontal, oblique, basilar, and lateral photographs in repose and animation are essential. Posteroanterior and lateral cephalograms, as well as a panoramic X-ray, can also be helpful. Any evaluation of the lower third of the face should also include the following points:
In a youthful midface, the superior border of the triangular shaped malar fat pad lies along the orbital rim and extends laterally to the zygomas (Fig. 35.1). The lateral border can be identified by drawing a line from the lateral canthus to the lateral commissure. The malar fat pad is located beneath the skin and subcutaneous fat, but it is superficial to the superficial muscular aponeurotic system (SMAS). It is fibrous and fatty, and it is readily distinguishable from the overlying subcutaneous fat. With advancing age, the malar fat pad descends inferiorly and medially. Ptosis of the malar fat pad empties the midface and accentuates tear-trough and nasolabial folds. To a lesser extent, this displacement also results in the formation of labiomandibular folds (marionette lines) and jowls.
Fig. 35.1 In a youthful midface, the superior border of the triangular shaped malar fat pad lies along the orbital rim and extends laterally to the zygomas. With advancing age, the malar fat pad descends inferiorly and medially. Ptosis of the malar fat pad empties the midface and accentuates the tear-trough, nasolabial folds, labiomandibular folds (marionette lines), and jowls.
The cutaneous insertion of the zygomaticus major/minor and levator labii superioris muscles determines the nasolabial fold. In a sense, the nasolabial fold may be considered a fasciocutaneous ligament necessary for lip elevating muscles to initiate a smile. Laxity of this fasciocutaneous ligament causes the malar fat pad to travel inferomedially over the crease to deepen the nasolabial fold.
On profile, the upper lip ideally projects approximately 2 mm beyond the lower lip, which, in turn, ideally projects 2 mm beyond the most anterior aspect of the chin (the soft-tissue pogonion). The lower lip is normally fuller than the upper lip. The fullness of the lower lip determines the inclination of the lower lip, which affects the appearance of the chin.
The position of the labiomental fold contributes to the appearance of the vertical height of the chin. A high labiomental fold will make the chin appear larger, and a low labiomental fold will make the chin appear smaller and more defined. A shallow or indistinct labiomental fold makes the chin appear larger because the demarcation between the lower lip and the chin pad is less well defined. The surgeon can also imagine the labiomental fold in profile as an angle (Fig. 35.2). A shallow fold has an obtuse angle and a deep fold has a more acute angle. Viewing the labiomental fold as an angle can be helpful when planning chin surgery. For example, performing an augmentation genioplasty on a patient with a low, deep labiomental fold will make the fold angle more acute and the fold will appear too deep.
In conjunction with the labiomental fold, the inclination of the lower lip also affects one’s perception of chin size. The lower lip inclination helps to create a demarcation between the lip and the chin pad. Therefore, the more vertical the lower lip, the larger the chin appears.
Dental occlusion also affects the appearance of the lower-third of the face. For example, a deep bite may contribute to lower lip eversion with an oblique inclination as well as an acute angle at the labiomental fold. It is important to assess dental occlusion and inquire about prior orthodontic or orthognathic treatment. The treatment of patients with Angle Class II or Class III malocclusion is beyond the scope of this chapter.
The chin pad is assessed by palpation. Chin pad soft tissue projection should be maximally at the level of the pogonion (Fig. 35.3). Static chin pad position should be noted. A chin pad cleft represents a cleft in the mentalis muscle as well as a deficiency of the chin pad soft tissue.
It is important to assess the size of the bony chin, especially in the case of the large chin. This is accomplished through palpation and dynamic evaluation: when smiling, a large chin due to a large bony component becomes even more pronounced, whereas a large chin due to excess soft tissue will appears better as the soft-tissue becomes effaced. Cephalograms are especially useful in determining the size and shape of the bony component.
The vertical height of the chin extends from the menton to the nadir of the labiomental fold. The appearance of the chin is affected not only by the size of the bony chin, but also by the pad percentage and the height and distinctness of the labiomental fold.
Normally, maximal chin projection is at the level of the pogonion. In some patients, there is a prominent symphyseal ridge or bulky mentalis muscle which causes increased chin projection just below the labiomental fold. In some cases, bony reduction is indicated.
During a normal smile, the zygomaticus and levator labii superius muscles elevate the corners of the mouth moving the chin pad superiorly. Some patients have a horizontal, non-lifting smile. Patients with a horizontal smile have unbalanced lower lip depressor (e.g. depressor labii inferioris or depressor anguli oris) activity which causes dynamic chin pad ptosis with smiling.