What is Masseter Muscle Hypertrophy

Dr. Kinda NassriFace

Masseter Muscle Hypertrophy

Masseter Muscle Hypertrophy (MMH) is a condition where one of the muscles responsible for mastication (or chewing) got enlarged prominently. The masseter muscle is the main muscle that pulls the jaw up to close the mouth. The increase in Masseter muscle activity and size can leave the patient with a cosmetic concern and/or medical complaint.

How MMH effects patient life?

People with MMH usually complains of square shape faces or wide faces with no cheek projection. It can be lateral or unilateral that manifests as a facial asymmetry.

Moreover, Medical complains associated with MMH can be:

Bruxism; unintentional habit of grinding of the teeth during sleeping. Leading to disrupted sleeping, facial pain, headache, earache and worn- down teeth.

Trismus, known as Temporomandibular Joint (TMJ) Disorder; spasm of the jaw muscles causing the mouth to remain tightly and temporarily closed.

Many studies have shown that these cosmetic and medical changes can negatively affect patient’ mental and physical health.

What are the reasons behind MMH?

There is no specific cause for MMH. But it can be either or all:

  • Congenital; Masseter muscles are originally big, strong, and protruded
  • Functional; Hyperactivity of the masseter muscles in which bruxism or trismus are present
  • Emotional; due to stress and nervousness

How MMH can be diagnosed?

Through history taking and physical examination, the Doctor will conclude the diagnosis of MMH.

After the facial assessment, you will be told to bite down on your teeth and the Doctor will feel the shape and the size of the muscle to determine the need and the proper treatment for each case.

What kind of treatment can be best offered?

Once MMH is diagnosed, Botox injection into the masseter muscles will be offered as a non-surgical procedure.

Botox (Botulinum Toxin) has many indications, but it is known to be used in aesthetic medicine to treat facial expression wrinkles. It is a protein that temporarily relaxes muscle activity to reduce its function. Over time, with repetitive masseter muscle Botox injections, the goal is to weaken the muscle, so it atrophies (reduced in size). Hence, it helps in alleviating the bruxism/ TMJ severity and giving more harmony to the face. In exceedingly rare and selected incidence, surgery might be an option to mitigate such aggressive cases.

Who is a good candidate for Botox?

Usually, patients with a wider lower down of the face are more frequently coming for Botox treatment. Slimming the face to have a better cheek projection and smoother jaw jawline appearance is a way to feminize the face. However, male patients who consider their jaw to be too wide or too square have the option to remodel the area to be more balanced with the rest of the face.

Meanwhile, patients with severe bruxism or trismus that are using mouth guard/ splint, or are on medications, can dramatically reduce its severity with Botox injection. This treatment will allow them to lessen the need to use other methods of alleviation as well.

However, though the width can be due to MMH, it is also can be related to an excess of fat in that region for which Botox has no effect at all. In such cases of an excessive fat thickness (chubby faces), Doctor will discuss other treatments for face slimming. Treatment can involve surgical partial removal of the fat pad or enhancing the cheekbones with fillers in conjunction with masseter muscle Botox injection or not.

Some patients have big protruded mandibular angles (angle of the jaw) that remarkably play a major role in face width and shape, and for that, they are not considered a suitable candidate for Botox treatment.

Patients with moderate to severe saggy facial tissue are advised not to do this procedure as it can worsen the case.

Always remember, proper consultation and assessment by the specialist is needed to determine the right candidate for the right treatment.

What can Botox do and can’t do?

– Botox can reduce the Masseter muscle volume and contractions while preserving its main function.

– Botox can help to give a more oval face shape by sliming the posterior lower cheek area (Muscle) but not the anterior lower cheek area (fat).

– Botox can’t degrade fat.

– Botox can’t give a facelift.

– Botox can help in remodeling the face but can’t be always enough as a single treatment.

Where will be the injections placed?

After cleaning and marking the muscle border with a pencil. The doctor will palpate the bulk of the muscle while the patient is clenching his teeth. 3- 5 deep intramuscular injections will be preceded with a specific Botox dose depending on each case severity.

The patient will be told not to massage the area and to restrain any form of exercise for 24 hours.

What to expect after Masseter muscles Botox injection?

As the Botox effect will kick on gradually over the next few weeks, the best results will be witnessed only after 6- 8 weeks of the treatment. An initial assessment can be done at 3 weeks interval time to determine the need for extra Botox dosage.

Because the Masseter muscle is a big and strong muscle that is used consistently during the day, the duration of the Botox effect is considered shorter comparing to other muscles typically treated (ex; upper face muscles). Masseter muscles begin to recover their function over the following 3-4 months and to increase in size after 4-6 months of the injection. However, some case reports describe the effect to last 4-10 months long.

Repetitive Botox treatment can weaken and thin the masseter muscles and further Botox dosage and frequency can be lessened with time.



Anehosur, V., Mehra, A., & Kumar, N. (2020). Management of masseter muscle hypertrophy and role of adjunctive surgical procedures. Craniomaxillofacial Trauma & Reconstruction Open, 5, 2472751220913147.

Connelly, S. T., Myung, J., Gupta, R., Tartaglia, G. M., Gizdulich, A., Yang, J., & Silva, R. (2017). Clinical outcomes of Botox injections for chronic temporomandibular disorders: do we understand how Botox works on muscle, pain, and the brain?. International journal of oral and maxillofacial surgery, 46(3), 322-327.

Fedorowicz, Z., van Zuuren, E. J., & Schoones, J. (2013). Botulinum toxin for masseter hypertrophy. Cochrane Database of Systematic Reviews, (9).

Lee, H. J., Kim, S. J., Lee, K. J., Yu, H. S., & Baik, H. S. (2017). Repeated injections of botulinum toxin into the masseter muscle induce bony changes in human adults: A longitudinal study. Korean journal of orthodontics, 47(4), 222.

Nestor, M., Ablon, G., & Pickett, A. (2017). Key parameters for the use of abobotulinumtoxinA in aesthetics: onset and duration. Aesthetic surgery journal, 37(suppl_1), S20-S31.

Sharad, J. (2015). Contouring of lower face with injection of botulinum toxin into the masseter muscle. J Appl Aesthetics.