The mentalis muscle is a paired central muscle of the lower lip, situated at the tip of the chin.[1] It originates from the mentum of the mandible, and inserts into the soft tissue of the chin. It is sometimes referred to as the "pouting muscle" due to it raising the lower lip and causing chin wrinkles.
The mentalis muscle causes a weak upward-inward movement of the soft tissue complex of the chin.[2] This raises the central portion of the lower lip.[2] In the setting of lip incompetence (the upper and lower lips not touching each other at rest), the contraction of the mentalis muscle can bring temporary but strained oral competence.
In conjunction with the orbicularis oris muscle (for the upper lip), the mentalis muscle allows the lips to "pout". Externally, contraction of the mentalis muscle causes wrinkling and dimpling of the skin on the chin, as used in expressions of doubt or displeasure.[4]
Clinical significance
The mentalis muscle can be easily assessed using ultrasound.[5]
The mentalis muscle may be partially paralysed using botulinum toxin to reduce wrinkling of the skin of the chin.[4] This may be done for cosmetic purposes.[4]
Additional images
Outer surface of mandible. Mentalis is indicated by the red circle at left.