Jaw muscle and teeth grinding

The masseter is the strongest of the chewing muscles. It sits at the angle of the jaw and closes the lower jaw. In night-time grinding or clenching — bruxism — it works for hours against a resistance the body never intended. Like any muscle under load, it grows in volume.

Two complaints, one cause.

One reason to treat is functional: a stiff jaw in the morning, tenderness in front of the ear, tension headaches in the temples, wear on the teeth, sometimes clicking in the joint. Dentists usually start with a splint, which protects the teeth — but it does not reduce the muscle activity itself.

The other reason is shape: a hypertrophied masseter widens the jaw angle and makes the lower face look more angular and square. The two often occur together, and both trace back to the same overactivity.

How the treatment works.

The medication used reduces the muscle's contractile force for a limited period. It is injected into the lower, superficial portion of the masseter, at a defined distance from the neighbouring muscles of facial expression. Clenching force decreases; the ability to chew normal food is retained, because other muscles contribute to it.

Relief sets in after roughly one to two weeks. A visible reduction in muscle volume — if that is even the goal — appears considerably later, usually after six to eight weeks, because it depends on reduced load. In this area the effect often lasts longer than in the face, frequently four to six months.

Side effects — named honestly.

In the first one to two weeks chewing firm food can feel tiring. Small bruises are possible. With too high a dose, or an injection placed too far forward, the smile can look temporarily asymmetric because neighbouring muscles are affected. With repeated treatment over long periods a lasting reduction in muscle volume is possible, which is not always desirable. A residual risk cannot be excluded entirely.

When treatment is not the right answer.

Bruxism usually has other components: stress, disturbed sleep, a misaligned bite, in some cases a sleep-related breathing disorder. Treating the muscle does not replace investigating those. Where jaw joint symptoms are pronounced, the dental or orthodontic assessment belongs at the start, not at the end. If the jaw angle is already narrow and the face slim, we advise against treating for shape.