The mentalis is the primary muscle of chin expression, producing the characteristic cobblestone or dimpled chin appearance of uncertainty, pouting, or effort. It elevates the lower lip and protrudes it slightly, the gesture associated with drinking from a cup, expressing doubt, or forcefully closing the lower lip against the upper. The chin prominences visible in normal movement are produced by the mentalis pushing against the subcutaneous chin fat.
| Origin | Incisive fossa of the mandible below the roots of the central incisors |
|---|---|
| Insertion | Skin of the chin |
| Nerve Supply | Marginal mandibular branch of the facial nerve (CN VII) |
| Blood Supply | Mental branch of the inferior alveolar artery |
| Actions |
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By elevating and everting the lower lip it assists in drinking and oral continence, and its chin-wrinkling action creates the social signals of displeasure or uncertainty that are important in human non-verbal communication.
Mentalis muscle overactivity producing persistent chin wrinkling at rest is a common aesthetic concern treated effectively with botulinum toxin injection. Orthognathic surgery and genioplasty procedures detach and must meticulously reattach the mentalis to prevent ptosis of the soft tissue chin (witch's chin deformity), the most common soft tissue complication of mandibular surgery. Mental nerve damage during apical surgery on lower incisors can produce chin numbness mimicking mentalis dysfunction.
The mentalis is palpable as the paired muscle bellies on either side of the chin midline beneath the lower lip, becoming firm during chin protrusion or the attempt to elevate the lower lip against resistance.
Soft tissue chin ptosis from mentalis muscle detachment during orthognathic or chin surgery, producing a drooping soft chin that requires surgical muscle reattachment and subperiosteal suspension to correct.
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