Why inject botox into the masseter muscle?
Botox has many benefits. One of the common places we inject is into the masseter muscle, the muscle which cups the outer jawline. Doing Botox in this muscle doesn’t affect anything noticeably in your ability to talk or eat. So why do it?
Botox in the masseter is great for TMJ. Do you clench? grind? Have you had broken teeth or are grinding your teeth down? Do you wake up with a sore jaw? Headaches?
Many of us in the Bay Area have stressful busy lives, and we take that out at night on our teeth.
But the other benefit of doing botox in the masseter muscle is it helps narrow the jawline. I can tell when I see a patient if they are a teeth grinder. They ask, “How did you know?” I can see it in the prominence of the muscle. When the masseter muscle is built up, the face has a wide, square or trapezoidal lower facial shape, which they may not like. So for many, they seek the cosmetic benefit of treating what we call “masseter hypertrophy.” In English, that means you have a big beefy jaw muscle, which widens the jawline and face.
Study: Controlled trial to look at efficacy and safety of a single injection
This will be a quick blog, because you are speaking to the choir here. This was a study published in the October 2025 Aesthetic Surgery Journal, “A Controlled Phase 2b Trial to Assess the Efficacy and Safety of a Single Intervention of Onabotulinumtoxin A for Treating Masseter Muscle Prominence.”
Study:
- They graded masseter muscle prominence “MMP” on a 5 grade scale.
- Participants were randomized to placebo, 48 units, or 72 units
- Findings? “Significantly greater proportion got a MMP score of Grade 3 or less when on botox vs. placebo
- Interestingly the rate was 90.6% on 48 units, 91.3% on 72 units, and 21.7% on placebo at day 90.
- Significant reductions in the width of the lower face, peaking at day 90
- Improvement in mandibular facial angle 1C (indicating a more oval face)
Dr. Greenberg’s thoughts on botox into the masseter
I love it. I love it for the TMJ benefits (and have used it myself as I have had issues with TMJ in the past) and I love the facial slimming effects for those with a built up muscle. I have patients who have cracked teeth and have daily morning headaches from clenching and grinding at night. This fixes it.
It was interesting to see the amounts they used. We usually do 24 units for the masseter, and in this study they did 48 and 72. Interestingly there was equivalency between the results at 90 days between 48 and 72 units, so it would seem the lower number is better- cheaper, same efficacy. I wish they would have done 24 units as well. Or tracked it longer to see if the higher dose lasted longer.
I had not heard of the MMP score before. It tells the severity. 1= minimal, 2 = mild, 3= moderate ,4= marked, 5= very marked.
Regardless, I love it. I am a fan.
Medical citation
A Controlled Phase 2b Trial to Assess the Efficacy and Safety of a Single Intervention of OnabotulinumtoxinA for Treating Masseter Muscle Prominence , Aethetic Surgery Journal October 2025
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