Horizontal and oblique lines form across the bridge and side of the nose due to contraction of the transverse nasalis muscle and often become more prominent after BoNT-A treatment of the glabella.17,27 Rhytides are oriented perpendicular to the muscle fibers of the underlying nasalis muscle.29 Wrinkle severity, muscle mass, degree and duration of effect, and adjacent muscle function are the primary considerations in adjusting the BoNT-A dose. To prevent excessive paralysis of the deeper and more inferior levator labii superioris and levator labii alaeque nasi, important elevators of the upper lip, injection sites should be high on the nose and superficial. Excessive chemodenervation of these muscles may lead to upper lip ptosis.29
Smoking, aging, and habitual facial expressions can result in changes to the appearance of the lips, particularly the formation of vertical perioral rhytids. The muscles in the region most commonly addressed with BoNT-As are the orbicularis oris, depressor anguli oris (DAO), and mentalis.29 The patient’s pattern of recruitment of the orbicularis oris (the “pout” pattern) can guide the location of injections.26 In general, injections should be symmetrical and superficial.26 Overdosing can result in perioral muscle weakness, lip elevation, or lip depression, and slight differences in injection depth or placement on either side of the midline can lead to facial asymmetry.38 Considerations for dose adjustment include muscle mass, wrinkle severity, desired degree and duration of effect, and function of adjacent muscles.27 The number of injection sites varies. Outcomes are often enhanced when BoNT-A is combined with soft tissue fillers and/or resurfacing.26
The DAO muscle depresses the angle of the mouth and pulls down on the oral commissures, creating rhytides from the corners of the mouth to the jaw that can be particularly troubling as patients age. Weakening the DAO with BoNT-A minimizes downward pull on the dermal insertions of the muscle and can raise the oral commissures.26 Observed muscle action is of primary importance for locating injection points, but superficial landmarks can play a secondary role. Muscle weakness and an asymmetric smile resulting from BoNT-A diffusion into the depressor labii inferioris are possible adverse events in this area. Careful, symmetric placement of injections away from the oral commissures, along with proper dosing, reduces the risk of adverse effects.27 The lower third of the DAO should be targeted to avoid injecting the depressor labii inferioris.39 Dosing is adjusted based on muscle mass and adjacent muscle function, as well as wrinkle severity to a lesser extent.27
The appearance of a dimpled chin due to mentalis muscle contraction can be reduced with the use of BoNT-A, although toxin is best used conservatively in this area.26 Injection points should be located mostly by observed muscle action but also based on superficial landmarks. Muscle mass, adjacent muscle function, desired degree and duration of effect, and wrinkle severity are important factors when adjusting the usual dose.27
There were differing opinions about injection depth in this area, as well as the number of injection points. Several panelists keep injections superficial in the chin because the mentalis muscle is intercalated with the skin, and that is one way to avoid complications, since it keeps BoNT-A out of the lip depressor areas. Others do 4 injections, with the 2 lower injections deep and the 2 upper injections superficial, noting it gives excellent results while avoiding lip dysfunction. One panelist believes that with paired injections, the needle might actually be at different levels, resulting in some lip dysfunction and asymmetry. This panelist typically uses a single, deep, central bolus retrograde injection, almost down to the bone, and continues to inject as the needle is withdrawn, so it is deep and superficial. This affects the body of the medial portion of the paired mentalis as well as getting near the dermal insertions to improve skin texture in this area.
The group agreed that treating the mentalis can be difficult due to the amount of recruitment in the area. When using a BoNT-A with a tight field of effect, there is good paralysis in the injection area, but the lateral part of the mentalis may start bulging. It was suggested that increasing the dilution to get a little bit more diffusion or increasing the number of injection points would be beneficial in that situation.
Hypertrophy of the masseter muscle can create a square-jawed profile that can be considered unattractive, especially in women and in certain cultures.27,29 Unlike most other aesthetic uses of BoNT-A, which diminish wrinkles or correct asymmetry, treatment of the masseter is intended to reduce muscle mass by atrophy, slimming the jawline.27,29 Observed muscle action and muscle palpation are the most important factors for locating injection points, with minor roles for superficial landmarks and anatomic diagrams. Treatment of this area is challenging even for experienced aesthetic physicians.27 Care should be taken to avoid excessive paralysis, as it can weaken mastication.29 The panel agreed that they see more masseter hypertrophy in young women under age 35 than in older patients. Recognizing and treating these young women with tremendous masseter