๐ ็ธฝ็ฎ้ ๏ฝ ๐ ่ฑๆๅๆ๏ผๆฌ็ฏ๏ผ ๏ฝ ๐ ๅฎๆด็ฟป่ญฏ ๏ฝ โญ ็ฒพ่ฏ็ญ่จ
Masseters
Masseters
Masseteric hypertrophy conveys the impression of heaviness and squaring of the lower face. Genetic predisposition and mastication habits contribute to the development of this feature that is often considered aesthetically displeasing, especially in women as it can masculinize the face. A significant body of evidence supports the use of BTX in the reduction of unwanted masseteric hypertrophy. All commercially available type A botulinum toxins have been utilized successfully for this purpose.70,82,83 Anatomic considerations should be taken into account when selecting the appropriate injection points for neuromodulator contouring of the masseters.84 Misplaced injections can result in disturbance of the risorius muscle and resultant facial asymmetry. Injection of neuromodulators deep and directly into the belly of the masseter muscle may diminish the risk of unwanted diffusion. The following technique can be used to optimize safety and efficacy of treatment in this area. First, palpate the point of maximal muscle hypertrophy upon clenching along the mandibular border and mark this as the primary injection point. Next, administer two adjunctive injections approximately 1 cm superolateral and 1 cm superomedial, in the shape of an inverted triangle, keeping the superomedial injection point 1 cm posterior to the medial border of the masseter. By remaining inferior and lateral along the muscle, the risk of adversely affecting the zygomaticus major and risorius muscles is decreased. A total of 20 to 30 units of ONA may be injected into each muscle initially, depending on the degree of hypertrophy. Utilization of multiple injection points as opposed to single injection minimizes the risk of imbalanced muscle atrophy (Fig. 57-11). A follow-up visit is scheduled 4 weeks after injection for additional slimming of the muscle if necessary to achieve the desired facial contour (Fig. 57-12).
Downturned oral commissures The depressor anguli oris (DAO) originates at the outer surface of the mandible posterior to the oblique line and inserts into the modiolus at the angle of the mouth. It is innervated by the mandibular branch of the facial nerve and serves primarily to depress the oral commissure. A hyperactive DAO contributes to the accentuation of the melomental fold (marionette line) and creates an impression of disapproval and sadness. It can also lend an appearance of an aged lower face. Chemodenervation of the DAO via application of ONA can improve this appearance and create the impression of a more youthful and vibrant outlook. However, placement and dosage of medication must be carefully considered. The modiolus is an insertion point for several key muscles of facial expression, including the zygomaticus major, risorius, levator anguli oris, orbicularis oris, DAO, and depressor labii inferioris (DLI). As such, misplacement of neuromodulator in this area has the potential to negatively alter expressivity, phonation, and facial symmetry. Recent anatomical studies have shed light on the appropriate location for safe injection of neuromodulator targeting the DAO.84 Prior to injection, to avoid treatment of the DLI when injecting along its insertion on the mandible, patients are asked to pull down the corners of their mouths to aid in the location of the DAO. Following this landmark identification, 4 units of ONA are injected into the DAO on each side along the mandibular border staying 1 cm lateral to the oral commissure.85 In this fashion, the fan-shaped belly of the DAO is most accurately targeted while minimizing the possibility of medication diffusion affecting adjacent musculature.
Chin wrinkling The mentalis muscle is the primary evertor of the lower lip and also serves to elevate the skin of the chin. Its fibers intermingle with the orbicularis oris and DLI.86 A hyperdynamic mentalis muscle can create unwanted wrinkling and creasing with a peau dโorange appearance. Appreciation of this effect is best noticed when the patient is performing facial expressions. Correction of this phenomenon can be achieved with the injection of either 4 units of ONA directly into the insertion point of both bellies of the mentalis muscle centrally on the mandible or 2 units of ONA into each belly of the muscle, staying close to the midline to avoid spread to the DLI (Fig. 57-8). It is also important to place injections deep to avoid the more superficial DLI.
Neck and chest Excessive platysmal banding is an increasingly common problem with aging. The vertical banding is a result of platysmal muscle hypertrophy. Treatment of this area should be performed in a series of injection points delivered superficially. Injections begin at the jawline and proceed inferiorly along the band with approximately 2 cm spacing. Each injection point should deliver 5 to 10 units of ONA and the maximum dose per side should not exceed 50 units (Fig. 57-13).78,87
Dรฉcolletรฉ wrinkles have also been shown to respond to BTX therapy. In this setting, a V-shaped pattern of injection points following the distribution of โnecklace linesโ
should be utilized. Each injection is delivered at a depth of 4 mm with 5 to 10 units of ONA per injection site. The total dosage typically ranges between 75 and 120 units.78,87
Interestingly, flushing of the chest may also respond and improve with this treatment.88
Figure 57-8. Orbicularis oris and mentalis injection.
Figure 57-11. Imbalanced atrophy of the masseter muscle. This patient was treated with a single injection point into the masseter muscle and developed excessive atrophy at that point while simultaneously developing relatively abnormal hyperactivity in untreated areas. Left panel: At rest. Middle panel: Clenching the jaw. Right panel: Clenching the jaw at 45-degree angle photograph.
Figure 57-12. Before and after masseter muscle reduction. Note the slimming of the lower face contour, a subtle but pleasing aesthetic effect.
Figure 57-13. Platysmal band injection. Once again, treatment should be tailored to match each individualโs unique anatomical variations.