What is the masseter, and how does it grow?
The masseter is the main chewing muscle that pulls the lower jaw towards the upper jaw. It extends from in front of the ear to the corner of the jaw. Genetics, gender, eating habits (hard food, chewing gum), and stress-related teeth clenching habits affect masseter volume. An overdeveloped masseter gives a "square jaw" appearance; this is a characteristic in some men and a cause for complaint in some women.
The growth of the masseter is gradual and spans many years. Generally, volume increase accelerates in the 20s and peaks in the 30s. Unilateral contraction (always chewing on the same side) can cause asymmetry — one side may be more developed. This asymmetry can be corrected with masseter botox.
The treatment has two separate indications
The first is aesthetic: an aesthetic treatment that slims the facial line, softens the jaw angle, and balances the lower face. It is frequently preferred, especially in female patients aiming for a heart/oval face. The second is medical: it reduces muscle hyperactivity in patients with nocturnal teeth clenching (bruxism) and daytime teeth clenching. These patients have symptoms such as tooth decay, temporomandibular joint pain (TMJ), and morning headaches, and masseter botox reduces these symptoms by 70-90%.
The two indications usually combine in the same patient. A patient who comes for aesthetic reasons often has a history of teeth clenching or jaw pain; a patient who comes for medical reasons also experiences facial slimming. This dual effect makes masseter treatment one of the applications that creates the most "sense of value" for patients.
Aesthetic goal
- Oval/heart face line
- Jaw angle softens
- Lower face slims
- Effect visible in 3 months
- Results last 6-8 months
Medical goal
- Teeth clenching/grinding decreases
- Morning jaw pain subsides
- TMJ clicking/pain alleviates
- Tooth wear slows down
- Headache frequency decreases
Dose and technique
A dose of 20-40 units (Botox/Xeomin equivalent) is applied for each side. The dose is higher in men. The injection is spread over three points: into the body of the masseter on each side; the needle is placed deep, close to the bone level. Superficial injection can cause an effect in the wrong place — such as a "frozen smile" or a dimple.
The effect is gradual: slight softening in 2-3 weeks, visible slimming in 6-8 weeks, full results in the 3rd month. The results last 6-8 months; in some patients, it extends up to 9 months because the muscle size has significantly decreased, and it takes time for it to return to its former volume. Therefore, masseter botox is usually repeated 1-2 times a year.
Clinical note:In bruxism patients, masseter botox only treats the symptom, not the cause. Root causes such as stress, anxiety, sleep disorders, and malocclusion (improper bite) should not be neglected. In the clinic, I manage these patients in parallel with a dentist and, if necessary, a neurologist.
Side effects and things to consider
Most common side effect: temporary chewing weakness. In the first 2-3 weeks, hard/tough foods (steak, nut shells, thick chewing gum) may be difficult to chew. This is temporary and normal. Rare side effect: smile asymmetry — if the needle goes too high into the zygomaticus area instead of the masseter, one side of the smile may drop. In this case, muscle recovery is awaited, and it normalizes within 2-3 months.
In long-term repeated treatments, the masseter may permanently shrink. This is usually the desired outcome, but it is possible for the patient to feel "my face has become too thin." Therefore, after 2-3 treatments, the decision of "continue or pause?" is made together with the patient. If completely stopped, the muscle partially returns to its former volume over time but may not be "exactly as before."