Jaw clenching, grinding and TMJ discomfort
An overworked masseter muscle produces morning jaw soreness, tension headaches and a squarer lower face. Relaxing it addresses the cause rather than the symptom.
The masseter runs from the cheekbone to the angle of the jaw and is the strongest muscle in the body by weight. Clenching and grinding, or bruxism, is largely involuntary and largely nocturnal, which is why most people discover it through consequences rather than through the act itself: waking with a tight jaw, headaches concentrated at the temples, aching teeth, or a dentist noting flattened enamel. Sustained overuse also enlarges the muscle, exactly as any muscle enlarges under load, progressively squaring and widening the lower face. Conventional management is usually a night guard, which protects the teeth from the force but does not reduce the force itself, so the muscle keeps working and the headaches often continue. Injecting botulinum toxin into the masseter reduces its contractile strength directly. The jaw still functions normally for chewing and speech, because the treatment reduces the excess rather than the function, but sustained clenching force drops and the pain and wear drop with it.
How we treat it
Treatment is a small number of injections into each masseter, placed by palpation with the patient clenching so the muscle’s bulk and borders are identified precisely. Dose matters considerably. Too little and the clenching force is not meaningfully reduced; too much, or badly placed, and chewing can feel weak or the smile can be affected if the toxin reaches neighbouring muscles. This is a treatment where anatomical knowledge is the whole of the outcome. Relief of aching and headache usually begins within one to two weeks. Visible slimming takes considerably longer, because the muscle has to atrophy from reduced use, which is a matter of months and is most apparent after a second or third treatment. Most patients repeat at three to six months initially, and many find the interval lengthens as the clenching habit itself settles. Where the picture suggests a joint problem rather than a muscular one, or where dental wear is advanced, referral to a dentist or oral surgeon is the right first step.
Medically reviewed by Dr. Sherwin Hariri, MD, Medical Director & Chief Longevity Physician. Last reviewed August 2026.
This page is for information only and is not medical advice. Suitability for any treatment is determined at consultation.
Common questions
Will masseter Botox stop me chewing normally?
No. The dose is calculated to reduce excessive clenching force while leaving normal function intact. Some patients notice mild fatigue when chewing something very tough during the first couple of weeks, which settles. Difficulty with ordinary eating is a sign the dose or placement was wrong, not an expected outcome.
How long before the jaw pain improves?
Most people notice reduced morning soreness and fewer tension headaches within one to two weeks, with full effect by around four weeks. Facial slimming lags well behind symptom relief, because it depends on the muscle gradually reducing in bulk, and typically becomes visible between two and four months.
Is this the same as a night guard?
They do different things. A guard is a physical barrier protecting the teeth from grinding force, but it does not reduce that force, so muscular pain and headaches often persist. Treating the muscle reduces the force at source. The two are frequently used together, particularly where there is dental wear to protect.
Will my face look thinner?
Usually, if the masseter is genuinely enlarged. The change is gradual and tends to read as a softer, more tapered lower face rather than an obvious alteration. If the muscle is not hypertrophied, slimming should not be expected, and in that case the treatment is being done for the clenching rather than the contour.
Other concerns
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