Key facts
- Self-check
- Fingers flat over the jaw angle, bite firmly: a hard mound that softens on relaxing suggests muscle
- See a dentist first
- Tooth wear or sensitivity, pain in the jaw, face or ear, clicking, locking or limited opening
- What botulinum toxin does
- Reduces masseter activity, so the muscle gradually loses the bulk that use created
- What it does not change
- The bony angle of the jaw, facial fat, loose skin, or the clenching habit
- Assessment
- Palpation clenched and relaxed, bone angle, profile, chin, smile and bite, skin support
- Doses
- Not given here; potency units are specific to each product and are set after examination
- Fee
- Quoted in writing after assessment; see how fees are quoted
How can you tell if clenching is behind a wide lower face?
You can get a first answer in a minute with a mirror and your fingers. Place the fingers flat over the angle of the jaw and bite down firmly. If a hard, defined mound rises under the fingers and softens when you relax, you are feeling a working masseter, and it may be part of the width you see. If little changes between clenching and relaxing, the width is more likely bone or soft tissue, and a muscle treatment would be aimed at the wrong structure.
Then look and ask. Look at the lower face from the front and from the side, and compare with photographs from some years ago, because the change is gradual and easy to miss. Ask whether the jaw feels tight or tired on waking, whether you clench with your teeth together during concentration or at the screen, whether one side feels stronger because you chew on it, and whether anyone has heard you grind at night. Many people clench without noticing, so a negative answer is not proof.
The self-check cannot tell you how much of the width is muscle, and it cannot tell you whether the clenching is a problem for the teeth or the jaw joint. That needs an examination, and for the teeth and joint it needs a dentist. The shorter post on jaw clenching and face shape explains why a wider jaw is often a stronger muscle.
When should you see a dentist first, before anything cosmetic?
See a dentist first if you grind or clench and have tooth damage or sensitive teeth, pain in the jaw, face or ear, or a partner who hears grinding in your sleep. The NHS gives the same list for seeing a dentist. A dentist can examine the wear on the teeth, advise on a night guard where it is indicated, and look at the bite, none of which an injection can do.
Jaw pain, clicking, locking or limited opening suggest a problem with the jaw joint itself, and these are assessed before anything cosmetic is planned. Active dental problems also go to a dentist first. The cause of the habit, which is often stress, disturbed sleep or other factors, is its own medical question; botulinum toxin lowers the force a muscle can generate but does not remove the reason for clenching, and it does not replace dental care.
A doctor who treats the masseter should ask about all of this. At this practice a history of clenching or grinding is part of the assessment rather than an afterthought, because it helps explain why the muscle has enlarged and shapes what is realistic.
“A wider jaw is often a stronger muscle, not a heavier face.”
Dr Sin YongOn masseter hypertrophy and face shape
How is masseter treatment assessed, and what does the examination look for?
The assessment separates four possible causes of lower-face width, because only one of them responds to botulinum toxin. Masseter hypertrophy is muscle. Buccal fat sits higher and further forward in the cheek and is fat, not muscle. Skin laxity blurs the jawline without widening the face. The bony angle of the mandible is skeletal, and no injectable changes bone. Dr Sin Yong palpates the muscle clenched and relaxed, assesses the angle of the jaw, looks at the profile and the chin, and considers how well the skin and soft tissue support the lower face.
The history covers clenching and grinding, previous dental and jaw problems, medicines, and general health. Botulinum toxin is not used with disorders of the junction between nerve and muscle such as myasthenia gravis, or with a known allergy to a component; it is deferred in pregnancy, while breastfeeding and where there is infection at the injection site, and some medicines and conditions call for caution. A lean face with soft tissue that is already less supported may be better left alone, and sometimes the assessment ends with advice to leave the jaw exactly as it is. A defined jaw is a feature, not a diagnosis.
No doses are given on this page. Potency units are specific to each product's own assay and cannot be converted between products, so a figure quoted by another clinic using a different formulation is not comparable. Dosing and placement are decided on examination. The table sets out what masseter treatment changes and what it leaves alone.
What masseter treatment changes and what it leaves alone| Feature | Effect of botulinum toxin in the masseter | What else may apply |
|---|
| Muscle bulk at the jaw angle | Reduces gradually as the muscle works less | Response varies with bulk and anatomy; repeat decided at review |
| Bony angle of the jaw | No change; no injectable alters bone | Referral to a plastic or maxillofacial surgery specialist for skeletal width |
| Buccal fat and soft fullness | No change; fat is not muscle | Other approaches assessed after examination |
| Loose skin and soft jawline | May look less supported if muscle bulk falls | Lifting approaches considered where laxity is the cause |
| Clenching and grinding habit | Force falls while active; the habit remains | Dental review, night guard where indicated, stress contributors |
| Chewing and smile | Firm food may feel weaker; rarely the smile looks uneven | Reviewed if either is noticed |
What changes after masseter treatment, and what does not?
What changes is the activity and, gradually, the bulk of the masseter. Botulinum toxin blocks acetylcholine release at the junction between nerve and muscle, the muscle contracts less, and a muscle that works less loses the bulk that work built. The change is muscular and gradual rather than immediate, and response varies with muscle bulk, the degree of hypertrophy and individual anatomy. Some people notice less jaw tension or morning tightness as the force of clenching falls, while the habit itself continues.
What does not change is as important. A square bony angle remains square. Buccal fat is unaffected, so a round lower face in a lean person is not a masseter problem. Skin that has begun to sag may look less supported when muscle bulk falls, which is assessed before treatment. A V shape depends on the jaw angle, the length and projection of the chin and how cleanly the jawline runs between them, and masseter treatment addresses only the first. Where the chin is short or set back, chin projection or other approaches may change the taper more than any muscle treatment, and the jaw botulinum toxin page and the square jaw page compare the options.
Who should wait, and who is referred on?
Treatment waits for a dental or joint assessment if there is jaw pain, clicking, locking, limited opening or active dental disease, and during pregnancy and breastfeeding. It is also reconsidered where the width is not muscle: when the clench test shows no mound, the plan turns to fat, laxity or bone instead.
Width that is skeletal is not changed by any injectable, and where a bony angle is the concern, the discussion may involve referral to a plastic or maxillofacial surgery specialist for surgical options, with their trade-offs explained. Buccal fat that is removed surgically does not return, which is a reason for caution rather than enthusiasm. Where the true answer is that the face is balanced as it is, you will be told so.
What are the risks, and when should you call?
After treatment there may be small injection marks or a bruise. Some people notice that chewing firm or chewy food feels weaker for a period. Less commonly, the product affects a neighbouring muscle and the smile looks uneven, or a part of the masseter that was not treated bulges on clenching. Both are reasons for a review. Where skin laxity is already present, reducing muscle bulk can make the soft tissue look less supported. Effects are temporary as the muscle regains activity, and the decision about whether and when to repeat is made at review rather than in advance.
Call the clinic on +65 8023 7170 during clinic hours if your smile looks uneven, if one part of the muscle bulges, or if anything feels wrong. Difficulty swallowing, speaking or breathing after botulinum toxin is rare and is an emergency: go to A&E or call 995. The complication care page sets out when to seek urgent help.
What determines the fee for masseter treatment?
Singapore's rules prevent clinics from advertising prices, so no figures are given here. The fee follows the plan. What the examination finds the width to be made of is the first factor, because muscle, fat, laxity and bone call for different work. The size and strength of the muscle, if muscle it is, matters next, along with whether treatment is a single approach or staged alongside other contour work, and how the plan is reviewed over time.
A modest masseter in a slim face and a heavily built muscle in a strong grinder are different undertakings. Fees are written and itemised after consultation, and the how fees are quoted page explains what a quote contains. Dental care for the teeth, such as a night guard, is separate and is arranged with a dentist.
