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Page 8 of 12 Favre et al. Plast Aesthet Res 2020;7:71 I http://dx.doi.org/10.20517/2347-9264.2020.149

Figure 7. Injection sites for chin rhytids into the mentalis muscle

of this muscle can cause the lower face to look square, which is often not a desired appearance for female
patients. While the goal of treatment for the facial rhytids described above was to induce muscle paralysis,
the goal for BoNT-A injection of the masseter muscle is to soften the square appearance of the face by
[3]
reducing masseter muscle mass, ultimately creating a more desired aesthetic appearance . Dosage of
BoNT-A for injection is generally around 15 to 20 units of ONA, but the specific dosage depends on the
degree of hypertrophy. The effects of this injection can last six to nine months, but, as with other BoNT-A
injections, patients often follow up multiple weeks after injection to determine the need for more injections.
Factors such as bruxism and clenching habits can increase masseter muscle thickening and require more
[21]
frequent BoNT-A injections . In addition to BoNT-A’s aesthetic effects on the masseter muscle, patients
with temporomandibular joint dysfunction (TMJ) symptoms that have masseter hypertrophy report a relief
[10]
of their TMJ symptoms with BoNT-A injections .
The injector must be careful to avoid injecting the risorius muscle, which can result in the undesired side
effect of an asymmetric smile. It is important to inject inferiorly and laterally along the masseter muscle to
[3]
avoid this negative effect. In addition, overdosage of BoNT-A could result in inability to chew .

Platysmal bands
In addition to the upper, middle, and lower face, the neck is another region of the body where BoNT
treatment as a non-invasive procedure can be beneficial. The platysma muscle is the main muscle of the
neck. Unlike most muscles in the body, the platysma is located just below the epidermis and dermis in
the superficial layer of fascia. This location in relation to the skin is one of the reasons why this muscle is
an important muscle in aging. The platysma is a muscle of facial expression with many roles, including
depression of the mandible, depression of the corners of the mouth in frowning, and tensing of the skin of
the neck. Treatment with BoNT-A can counteract this downward pull in order to soften the appearance of
[10]
the neck and provide jawline definition .

Since the platysma muscle is located in the superficial layer of fascia, it is important to ensure that the
BoNT-A does not spread to the deeper muscles when injected. To prevent this spread, it is recommended
that the patient contract their platysma muscle in order for the physician to grasp the muscle with his/her
fingers and inject the neurotoxin at a superficial level. Injections not performed this way could result in
[22]
serious complications such as dysphagia .