Nerve supply to the face: trigeminal and facial nerves
Sensation is trigeminal with a cervical contribution; movement is facial. Confusing the two is the fastest route to misreading a complication.
Two separate nerve systems serve the face, and keeping them apart is the difference between correctly interpreting a post-treatment problem and guessing.
Sensation: trigeminal (V)
V1, ophthalmic — forehead, upper eyelid, nasal dorsum, cornea. Exits at the supraorbital and supratrochlear notches.
V2, maxillary — lower eyelid, cheek, lateral nose, upper lip. Exits at the infraorbital foramen, about a centimetre below the inferior orbital rim.
V3, mandibular — lower lip, chin, jaw; motor to the muscles of mastication. Exits at the mental foramen between the premolars.
The three exit points lie roughly on a vertical line in the mid-pupillary plane, which is a useful thing to have memorised. Each transmits a nerve alongside an artery, and each is a place where injected volume can compress the nerve and produce numbness or neuropathic pain.
Sensation: cervical plexus
Not everything below the eyes is trigeminal. The great auricular nerve from the cervical plexus (C2–C3) supplies the skin over the mandibular angle and much of the ear. It runs superficially across sternocleidomastoid with little cover.
Numbness over the mandibular angle after lower-face work therefore has a different explanation from numbness over the chin, and a practitioner assuming pure trigeminal distribution will misattribute it.
Movement: facial nerve (VII)
The facial nerve controls facial expression. It divides into temporal, zygomatic, buccal, mandibular and cervical branches, most of which run deep to the SMAS in the lateral face and become superficial as they approach their target muscles.
The temporal branch is the most vulnerable in aesthetic practice: it crosses the zygomatic arch superficially, and injury there produces brow droop that does not recover the way toxin effect does.
Reading a complication
- Numbness in a defined dermatome → sensory nerve, likely compression at a foramen.
- Weakness appearing over days → botulinum toxin diffusion, temporary.
- Weakness immediately after injection → mechanical or vascular, not toxin, and it needs assessment now.
- Numbness over the jaw angle → cervical plexus, not trigeminal.
Blocks follow the same map: small volumes at the supraorbital, infraorbital and mental foramina anaesthetise large territories comfortably.
