Medically reviewed by Dr Sin Yong · Last reviewed · 3 min read
Published 13 October 2026 · Reviewed by Dr Sin Yong
Masseter hypertrophy is enlargement of the masseter, the thick clenching muscle at the angle of the jaw, which, like any skeletal muscle, grows with training. Masseter hypertrophy's training is often involuntary: nocturnal bruxism, daytime clenching under stress and habitual gum-chewing are the classic loads. It is one of three materials that can widen the lower face, alongside bone and fat, and the only one that answers to botulinum toxin.
Key facts
What it is
Enlargement of the masseter, the clenching muscle at the jaw angle, from repeated load
Fingers flat on the jaw angles, clench hard: muscle hardens and bulges under the fingers; bone and fat do not
Treatment
Botulinum toxin to the masseter, dosed to preserve comfortable chewing, with the bruxism history addressed; bone and fat need different approaches
Where it fits
A wide lower face has three possible materials, and only one of them clenches. On the square jaw and masseter bulk page Dr Sin Yong settles the question in five seconds with the clench test and a bruxism history: muscle hardens under the fingertips, bony width is immobile and fat is soft and pinchable. Only masseter hypertrophy responds to botulinum toxin, dosed to preserve comfortable chewing; the treatment is described on jaw slimming with botulinum toxin. Grinding symptoms, morning jaw tightness, tension-type headaches and worn teeth, often coexist with the width, so the consult asks about sleep and the dentist first. A fat layer is treated with the Time Freeze Laser LCLR®, a dropped jawline with the VF Lift – Vertical Facelift; skeletal width is referred for surgical assessment. The injectable is defined under botulinum toxin.
No. A square jaw can come from an enlarged masseter, from the shape of the jawbone or from fat in the lower cheek. The clench test separates them, and only the muscular kind responds to botulinum toxin; injecting toxin into a bony or fatty width is a cost without a consequence.
Often. Treating an overactive masseter frequently relieves grinding, clenching and the associated tension symptoms, but the grinding that built the muscle also wears the teeth, so the dentist conversation belongs in the plan.
