CHAPTER 36 Alloplastic chin augmentation

History

Chin malformations can be due to any combination of soft tissue/bony excess, deficiency, or asymmetry. Consequently, treatment of a small chin with an implant is not always correct because all small chins are not the same. Moreover, not all implants are the same. Decisions regarding the surgical approach, implant size, type, and fixation depend on the following: (1) the thickness of the chin pad; (2) the chin pad percentage as a function of the height of labiomental fold; (3) the vertical height of the chin; (4) static ptosis; (5) dynamic pad ptosis with smile; (6) the inclination from the lower lip white roll to the labiomental fold; (7) the shape of the chin; and (8) the chin pad takeoff below the fold. Fortunately, the majority of patients who seek consultation for the treatment of a chin deformity suffer from a mild sagittal deficiency. This two-dimensional chin deficiency naturally lends itself to alloplastic augmentation at the lower border of the symphysis. However, unless the surgeon takes all of the above factors into consideration, a simple alloplastic chin augmentation may not deliver expected results. For example, surgeons continue to identify the sagittally deficient chin, but overlook the inclination of the lower lip and the height of the labiomental fold; this oversight leads to unanticipated outcomes. In sum, when making a treatment plan, your assessment must be right on or the “simple” alloplastic chin augmentation will deliver simply awful results.

The earliest chin implants, described by Gustave Aufricht in 1934, were made of autologous bony-cartilaginous tissue removed from the patient’s nasal dorsum. However, in the latter half of the 20th century, alloplastic chin augmentation became the operation of choice for enhancing a sagittally deficient chin. Alloplastic chin augmentation is deceptively simple because it can be performed on an outpatient basis with minimal equipment. The alloplastic material may at times be an alternative to an osteotomy. In general, alloplastic chin augmentation causes less pain, swelling, and bruising than an osteotomy. Furthermore, like a sliding genioplasty, alloplastic augmentation can fill lateral mandibular deficiencies and even improve the submental skin/soft tissue contour. There are a variety of alloplastic implant materials from which to choose: silicone elastomer, polyethylene, hydroxyapatite, etc. While chin implants primarily improve the sagittal projection of the pogonion, they also can augment the width of the chin immediately lateral to the symphysis. Alloplastic augmentation cannot change the vertical height of the chin, but augmentation often gives the illusion of a vertically longer chin. This chapter is devoted to an overview of alloplastic augmentation of the sagittally deficient chin.

Physical evaluation

The aesthetics of the chin must be evaluated in relation to the appearance and proportion of the face. Emphasis is placed on proper facial balance rather than anthropometric numerical standards. Whether dealing with a complex multidimensional soft and hard tissue chin deformity or a sagittal chin deficiency, we use a systematic assessment from the nose to the chin in order to reliably evaluate the nose, midface, lips, maxillomandibular dental relationship, chin pad thickness, labiomental fold depth and height, static chin pad position, and dynamic chin pad motion with smile. The patient’s aesthetic goals, as well as any previous surgical or orthodontic interventions are noted. The patient’s face is observed and photographed in repose and smiling from the frontal and profile views. Mandibular and/or mentum deficiency, excess, or asymmetry is documented. Below are some of the highlights of the nose-to-chin assessment:

Lower lip analysis

The inclination of the lower lip white roll to labiomental fold affects perception of chin size after augmentation or reduction (Fig. 36.1). If the inclination of the lower lip is vertical and the demarcation between the lip and chin is poor, the patient will appear to have an excessively large chin after augmentation. This is particularly true if a full height implant is incorrectly used. The lower lip analysis is intermingled with the labiomental fold analysis because the lip inclination helps define the labiomental fold. If a patient has a deep overbite and the lip is everted, then the lower lip will have an oblique inclination. The obliquity of the lower lip will contribute to a deeper labiomental fold with a more acute angle. The surgeon should note this because an alloplastic implant that is too tall will deepen the fold and make the labiomental fold angle even more acute. If it is helpful, the lower lip inclination can be classified as follows: Type I is nearly vertical, type II is slightly posterior, type III is significantly posterior, and type IV is most oblique.

Fig. 36.1 The inclination of the lower lip white roll to labiomental fold affects perception of chin size after augmentation or reduction. The classification of lip-to-labiomental fold inclination: type I is nearly vertical, type II is slightly posterior, type III is significantly posterior, and type IV is most oblique.

If two chins project exactly the same amount, the chin with the higher and/or shallower labiomental fold will always appear larger from the front (Fig. 36.2). Since the chin is primarily seen as the pad, the labiomental fold defines the apparent vertical height of the chin. Thus, augmenting a patient with a high, shallow labiomental fold tends to increase the appearance of the vertical height of the chin as well as its overall size. To overcome this problem, the surgeon should reduce the vertical height of the implant (see below) to limit augmentation to the lower pogonion. If the chin is long with a high fold, the patient may need both a vertical chin reduction and a sagittal augmentation. In contrast, a patient with a low, distinct labiomental fold will tolerate chin augmentation much better because the implant accentuates only the chin pad.

Fig. 36.2 Line drawings demonstrating that the position of the labiomental fold determines the chin pad percentage of the lower facial height. A, The relationship of the lip height to chin pad height is determined by the labiomental fold. B, High indistinct labiomental fold gives the illusion of a large chin. C, Low distinct labiomental fold gives the illusion of a smaller chin.

Static and dynamic chin pad analysis

The normal chin pad thickness is 8–11 mm. The chin pad thickness can be easily estimated by paramedian palpation. Soft tissue chin projection should be greatest at the lower part of the pogonion. The soft tissue chin pad position and static chin pad ptosis are noted. Chin pad clefting or fasciculations are documented. Since the chin pad is dynamic, soft tissues are also assessed during smiling.

The observer will note that when a chin pad is thick, a smile usually improves the patient’s appearance because the thick pad becomes effaced (Fig. 36.3). In contrast, as a thin chin pad is effaced upon smiling, the chin appears even more prominent (Fig. 36.4). During a normal smile, elevation of the corners of the mouth brings the chin pad superiorly. Some patients have a horizontal non-lifting smile such that the lower lip depressors are unopposed. Unopposed activation of the lower lip depressors produces dynamic chin pad ptosis with smiling as the chin pad drops (Fig. 36.5).