How to avoid mistakes when injecting masseter muscles with Botox

Dr Tim Pearce recently viewed a TikTok video of an American patient who was unhappy with her results after having her masseter muscles treated with botulinum toxin to relieve TMJ clenching and to contour her jawline.

In this blog, Dr Tim will discuss what may have happened in this case, sharing how aesthetic clinicians can learn to avoid similar outcomes when injecting the masseters with Botox®.

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Patient selection is critical when injecting masseter muscles with botulinum toxin

Dr Tim notes that watching patient videos like this one can be a great learning tool for aesthetic injectors. This case in particular provides multiple pointers that can help make practitioners safer and more effective, especially ensuring that you are treating the right patients with the right treatments and individually assessing suitability during the consultation.

As we listen to her experience, do pay attention to the different elements that she highlights. Firstly, there is an aesthetic judgment that she needed the treatment, which turns out not to be true. This is followed by a mention of a side effect, in this case the botulinum toxin affecting other muscles in the lower face, which is turn affected her smile. And, finally, she talks about a knock-on side effect of the result making her look older, with jowls.

Understanding mastication and the masseter muscles

The masseter muscles are the main muscles of mastication, for chewing. In some people they are hypertrophied, but masseter hypertrophy is not fully understood, explains Dr Tim. He suspects that there are many patients having masseter reduction treatments with botulinum toxin who do not know the underlying cause of the increase in size of their masseters.

Dr Tim interviewed Dr Ruth Brady in 2020 where he enjoyed her expert analysis of the masseter muscles and the use of botulinum toxin treatments. During the discussion, she explains in depth what causes hypertrophy of the masseter, including one theory that it is a malocclusion of the jaw. If the teeth are not closing neatly or tightly together, it can trigger a reflex whilst the person is sleeping that causes clenching. Similarly, biting down or clenching can also be associated with psychosomatic stress.

These present a couple of examples of discussion points that might arise during a consultation with a patient who wants to have their masseter treated. It is vital that aesthetic clinicians make sure to achieve the best result for their patients by treating the underlying cause and not just relaxing the muscle on every patient who has such complaints.

Dr Tim has also noticed that some aesthetic practitioners look only at the aesthetic when considering this treatment. This means that if a patient presents who will achieve a potential benefit from the slimming of that part of their face, the practitioner will inject all the way along the masseter aiming to get the maximum amount of slimming for them. Of course, this muscle is actively doing something in the face, thus relaxation will sometimes result in hypertrophy of the temporalis muscle, higher above, following repeated treatment of the masseter over a long time. Similarly, injecting the masseter quite superiorly means that you are very close to other nerves and other muscles in the face which can cause some very bad side effects.

He favours keeping injections very neatly in the lower third of the masseter muscle; this is slightly different to many textbook methods; however, he believes that it reduces the chance of impacting on the risorius muscle which pulls the corner of the mouth laterally and upwards when smiling; more on that in a moment.

What has gone wrong in this case; has the injector injected the masseters incorrectly?

As discussed, correct patient selection is critical; just because you can reduce the size of a masseter does not mean it is automatically the right thing to do. Not everyone can be made better looking with a slimmer lower face, warns Dr Tim.

In female patients, treatment will make the cheeks more dominant (with a narrower lower face) which is a key part of feminine beauty, but you cannot do that at the expense of a nicely defined jawline. If you reduce the amount of projection from the masseter, and if the masseter is not already projected outward creating an inverted triangle, you make the cheeks out of balance.

In the case of the lady in the video, she already has a nice angle of approximately 12 to 15 degrees, thus, treating her masseter is going to decrease her beauty. This is noted when she describes that after her treatment you could no longer see the definition of the lateral aspect of her jawline. She also noticed a small slump of tissue in a forward’s direction which gave her the start of a jowl, a terrible and ageing aesthetic result.

This is an important learning point to look out for in your aesthetic analysis of patients. In this case, she did not need reduction in the size of the masseter, and her masseters were giving her some support to her jowl. This meant the loss of volume allowed them to slip forwards and she started to see the formation of a jowl.

To prevent this problem, Dr Tim explains that it is important to realise that the bigger the masseter, the bigger the chance that it is supporting the jowl. If you shrink a very large masseter, even on a younger patient, you could start to get a shadow forming. The risk can be reduced by using a lower dose of botulinum toxin and accepting the smaller change in the size of the muscle for the benefit of avoiding significant volume change which would require further correction.

The patient also reported a complication where she felt that the botulinum toxin had spread into a different muscle which affected her smile. The most likely muscle to be affected is the risorius which is attached to the masseter muscle. If you inject the masseter muscle and placement is superior in the midsection, it is quite likely that you will hit the origin of the risorius muscle, reducing its strength and impacting on the creation of a broad smile.

Never underestimate the impact of affecting someone’s smile, it is one of the worst and most upsetting side effects for patients, due to the debilitating social impact.

To inject this area more safely, here are Dr Tim’s top tips.

• It is critical to understand that it is riskier to reduce the size of a masseter in an older patient because the slump forward of the tissue and jowl formation is more likely to occur, but as this case shows, it can also happen in younger patients.
• Be warned not to listen to patients who encourage you to inject higher up the masseter, which is quite common when they are seeking defined cheekbones. Treatment ought to focus on their cheeks rather than focusing entirely on reducing the size of the masseter muscle because potential side effects are increased as you go higher in the face, including proximity to the nerve plexus and the insertion point of risorius.
• When injecting, be very clear where that anterior boundary is location. It can be palpated quite easily as well as visualised; only inject the lower third of the muscle.
• Do not copy illustrations that you find on the Internet for masseter neurotoxin patterns. Most results will show a line drawn on the face, often from the tragus or the base of the earlobe running to the oral commissure. Beneath the line is said to be the safe area for injection; however, if you look closely at the diagrams, the origin of the risorius muscle is included in that area which is responsible for nearly all of the common side effects from treating the masseter. To reduce this risk, and still achieve the same results, Dr Tim instead draws the line to the mental crease which removes the origin of risorius.

It is vital to know your muscle anatomy to avoid side effects from Botox in the lower face. Why not get your hands on this beautiful anatomy poster, designed by Dr Tim Pearce as a useful reminder of all the muscles within the face.

If you have any questions or comments about botulinum toxin treatments to the masseter muscles and the lower face, you can find Dr Tim Pearce on Instagram.

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Dr Tim Pearce MBChB BSc (Hons) MRCGP founded his eLearning concept in 2016 in order to provide readily accessible BOTOX® and dermal filler online courses for fellow Medical Aesthetics practitioners. His objective was to raise standards within the industry – a principle which remains just as relevant today.

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