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Orbicularis oris muscle

The orbicularis oris is a complex, multi-layered muscle encircling the mouth. Often called the “kissing muscle,” it plays a crucial role in facial expression, speech, and mastication by controlling movements of the lips. This muscle forms the bulk of the lips and acts as a sphincter, enabling puckering, closing, and compressing the lips. Its anatomical relationships and significance in both function and imaging make it essential knowledge in clinical practice, dentistry, plastic surgery, and radiology.

Synonyms:

  • Kissing muscle

  • Sphincter muscle of the mouth

  • Orbicular muscle of the mouth

Function:

  • Closes and protrudes the lips (puckering)

  • Compresses the lips against the teeth

  • Aids in articulation of speech

  • Facilitates mastication by keeping food inside the mouth

  • Essential for facial expressions such as kissing, whistling, and blowing

Origin:

  • Maxilla (upper jaw)

  • Mandible (lower jaw)

  • Skin and fascia surrounding the mouth

  • Some fibers originate from neighboring muscles (buccinator, levator labii superioris, depressor anguli oris)

Insertion:

  • Skin and mucous membrane of the lips

  • Blends with fibers from other perioral muscles at the angle of the mouth (modiolus)

Nerve Supply:

  • Facial nerve (Cranial Nerve VII) — specifically, the buccal and marginal mandibular branches

Artery Supply:

  • Superior labial artery (branch of facial artery)

  • Inferior labial artery (branch of facial artery)

Vein Supply:

  • Superior labial vein

  • Inferior labial vein

  • Both drain into the facial vein

MRI Appearance:

  • T1-weighted images: Intermediate signal intensity, similar to other skeletal muscles

  • T2-weighted images: Normal muscle demonstrates relatively low signal intensity, but increased signal may indicate edema or pathology.

  • STIR (Short Tau Inversion Recovery): Muscle shows low signal intensity in healthy tissue; hyperintensity is seen if there is edema, inflammation, or acute injury.

CT Appearance:

  • Appears as a soft tissue density encircling the oral opening

  • Difficult to differentiate from surrounding soft tissues without contrast

MRI images

Orbicularis oris muscle mri axial image 1 -img-00000-00000

CT image

Orbicularis oris muscle CT axial image-img-00000-00000