The mentalis elevates and protrudes the lower lip, producing the pout expression and chin wrinkling. Mentalis hyperactivity compensates for lip incompetence (inability to close the lips at rest) — the characteristic chin strain seen during attempted lip closure in patients with overjet malocclusion. Botulinum toxin into the mentalis reduces chin wrinkling and the strain pattern.
| Origin | Incisive fossa of the mandible (anterior mandible between the mental foramina) |
|---|---|
| Insertion | Skin of the chin — the only facial muscle inserting entirely into the chin skin |
| Nerve Supply | Marginal mandibular branch of the facial nerve (VII) |
| Blood Supply | Mental artery (branch of the inferior alveolar) |
| Actions | Elevates the lower lip; Protrudes the lower lip (pout); Wrinkles the chin skin (the 'orange peel' chin of mentalis hyperactivity) |
|---|
Mentalis strain (chin dimpling and wrinkling during attempted lip closure) is the surface sign of lip incompetence — the mentalis hyperactivates to force the lower lip upward toward the upper lip. Orthognathic surgery correcting the overjet eliminates the mentalis strain. Isolated mentalis botulinum toxin injection (2-4 units) provides temporary relief of chin wrinkling.
The mentalis is palpable as the chin soft tissue between the mental foramina, becoming firm during lip protrusion and chin wrinkling.
Chin dimpling from mentalis overactivity compensating for lip incompetence managed with orthognathic correction or botulinum toxin injection.
