Topography and structure
The closed lips close the oral opening, and their free margins border the oral fissure (rima oris), the ends of which are called the angles of the mouth (anguli oris). At the angles of the mouth, the lips join into the lip commissures (commissurae labiorum).
Blood supply and innervation
- Motor innervation of the lips: facial nerve (n. facialis); the muscles of the lips include the buccal branches (rr. buccales) and the marginal mandibular branch (r. marginalis mandibulae).
- Sensory innervation of the angle of the mouth: buccal, infraorbital, and mental nerves (nn. buccalis, infraorbitalis, mentalis).
- Blood supply to the lips: superior and inferior labial arteries (aa. labiales superior et inferior), as well as the mental artery (a. mentalis). Venous drainage is carried out via the companion veins (vv. labialis superior et labiales inferiores).
Clinical examination
The condition of the angles of the mouth is assessed during dental and neurological examinations.
- Dental examination: when examining the oral vestibule, the physician evaluates the color of the vermilion border and the angles of the mouth, as well as the presence of scales and crusts. The examination is performed with clenched jaws and relaxed lips.
- Neurological examination: to assess the function of the lower facial muscles, the patient is asked to bare their teeth. Normally, the angles of the mouth are symmetrical. The patient is also asked to smile, puff out their cheeks, and blow out a match; the lips are protruded forward during this action.
Symptoms of lesions and diseases
- Facial nerve palsy: in peripheral neuron lesions on the affected side, the angle of the mouth is drooping, and when baring the teeth, the mouth deviates toward the healthy side. Speech and whistling are difficult, and liquids spill from the mouth. In central paralysis, drooping of the angle of the mouth and deviation of the mouth toward the healthy side when baring the teeth are also observed; the muscles of the lower face are affected.
- Tetanus: a specific sign is «risus sardonicus» (risus sardonicus). The face freezes, and the angles of the mouth are stretched and drooped.
- Eclampsia: in the first, initial period of the seizure, which lasts up to 30 seconds, the angles of the mouth are pulled downward against the background of fine fibrillary twitching of the facial muscles.
- Turner syndrome: sagging angles of the mouth belong to phenotypic facial features.
Class and exam questions
How is the symmetry of the angles of the mouth checked during a neurological examination?
The patient is asked to bare their teeth. Normally, the angles of the mouth are symmetrical. In facial nerve palsy, the mouth deviates toward the healthy side, and the angle of the mouth on the affected side is drooping.
Which nerves provide sensation in the area of the angles of the mouth?
Sensory innervation of the angle of the mouth is provided by the buccal, infraorbital, and mental nerves (nn. buccalis, infraorbitalis, mentalis).
What specific sign is described in tetanus?
Tetanus causes risus sardonicus (risus sardonicus): the angles of the mouth are stretched and drooped.
What else to study on this topic
- Orbicularis oris muscle
- Facial nerve (n. facialis)
- Oral vestibule (vestibulum oris)
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