How BTX acts on the jaw muscle
The masseter is the chewing muscle at the angle of the jaw. Botulinum toxin blocks the release of acetylcholine where nerve meets muscle. The muscle then contracts less. With reduced use, it loses bulk over the following weeks through disuse atrophy.
This treatment targets muscle only. If your width comes from something else, BTX will not change it. Dr Sin Yong checks the cause before advising you, and he performs the injections himself. The consultation also decides whether treatment is advised at all.
Four causes of a wide lower face
| Cause | Does BTX help? | What may be considered |
|---|---|---|
| Enlarged masseter muscle | Yes, this is what it treats | Masseter BTX |
| Buccal fat | No | Face slimming options |
| Skin laxity | No | Jowl treatment options |
| Bony width | No | A surgeon's opinion |
An enlarged muscle. This is the only cause that BTX treats.
BTX has no effect on it.
BTX does not tighten skin.
BTX does not change bone in any way.
Who is suited to masseter jaw slimming treatment in Singapore
Enlargement is confirmed by the clench test.
A wide lower face with habitual clenching or grinding.
Where muscle, not bone, drives the shape.
You accept change that is gradual and variable.
Who should wait
Please wait if you are pregnant or breastfeeding, or if you have an active infection or skin disease at the injection sites. It is also better to wait if you expect a V shape that depends on the chin or bone.
Who should not have it
For example, myasthenia gravis or Lambert-Eaton syndrome.
Known allergy to the product or its components.
Drugs affecting neuromuscular transmission, such as aminoglycosides, blood thinners, or a bleeding tendency.
Any existing difficulty with either.
Width from fat, laxity or bone.
Pain, clicking, locking or limited opening need assessment first.
What BTX cannot do
Buccal fat and bone width stay as they are.
Loose skin needs a different approach.
BTX does not build the chin.
Shape depends on more than the muscle.
Risks and side effects
Common effects are tenderness, small marks or bruising, chewing that tires more quickly for a period, and possibly headache. Less common effects are an uneven smile from spread to a neighbouring muscle, paradoxical bulging on clenching, and hollowing below the cheekbone. Difficulty swallowing is rare and needs urgent review. Risk is reduced by mapping the muscle, staying clear of smile muscles, dosing to the enlargement and reviewing you afterwards. A 2024 review of 46,250 patients in one clinic group recorded 223 followed-up adverse events, mostly paradoxical bulging, and all resolved. It counted only events seen at a return visit, so it does not capture everything.
What to expect
Dose and product
The dose is matched to muscle bulk, judged by feeling the muscle while you clench. The main formulation used has potency units specific to its own assay. These units cannot be swapped one-for-one with those of other botulinum toxin products. No unit figures are published, and the first dose stays conservative. It is a short in-clinic procedure. Avoid alcohol and strenuous exercise beforehand if advised. See also our page on anti-wrinkle injections.
Sessions and fees
The effect lasts a few months, and no duration is promised. Muscle regains activity as the effect fades. Repeat timing is decided at review, and intervals often lengthen as the muscle responds. Fees are not published. They depend on the area treated, what assessment finds, the product and amount, any combined treatment and staging. A written quote is given at consultation, after examination.