Parotid Region and Facial Nerve: Clinical Anatomy for Dentistry

Overview

The parotid region occupies the space between the ramus of the mandible, the external ear, and the masseter and sternocleidomastoid muscles. It contains the largest of the salivary glands and is crossed by the facial nerve, making it one of the most surgically hazardous zones of the head and neck. For the dental clinician it is essential in the diagnosis of salivary swellings, the interpretation of facial nerve palsy, and the safe conduct of extraoral procedures.

The Parotid Gland

The parotid is a purely serous gland lying in the retromandibular fossa, wrapped in a tough fibrous capsule derived from the investing layer of deep cervical fascia.

It has a superficial (larger) part overlying the masseter and a deep part extending medially toward the parapharyngeal space.
The gland is conventionally divided into superficial and deep lobes by the plane of the facial nerve, an artificial but surgically crucial landmark.
Accessory parotid tissue commonly lies along the duct on the masseter.

Structures Within the Gland

Three major structures pass through the parotid, arranged from superficial to deep:

Facial nerve (CN VII) — most superficial.
Retromandibular vein — formed by the superficial temporal and maxillary veins.
External carotid artery — deepest; it divides here into the superficial temporal and maxillary arteries.

The Parotid Duct (Stensen's Duct)

Emerges from the anterior border of the gland, runs horizontally across the masseter, then turns sharply to pierce the buccinator muscle.
Opens into the oral vestibule on a papilla opposite the crown of the maxillary second molar — the single most important intraoral landmark for the parotid.
Its surface projection follows the middle third of a line from the tragus to the midpoint of the philtrum.

Facial Nerve Course and Branches

The facial nerve exits the skull at the stylomastoid foramen, gives off branches to the posterior belly of digastric, stylohyoid, and posterior auricular muscles, then enters the parotid and divides at the pes anserinus into five terminal branches (mnemonic Ten Zebras Bit My Comb):

Temporal, Zygomatic, Buccal, Marginal Mandibular, and Cervical.
The marginal mandibular branch is especially vulnerable during submandibular surgery and extraoral incisions along the lower border of the mandible; injury causes drooping of the corner of the mouth.

Innervation of the Gland

Parasympathetic secretomotor fibres reach the parotid by a famously indirect route: glossopharyngeal nerve (CN IX) → tympanic nerve → lesser petrosal nerve → otic ganglion → auriculotemporal nerve (CN V3). The auriculotemporal nerve also carries the gland's sensory fibres, which explains referred pain to the ear in parotid disease.

Clinical Relevance

Mumps (epidemic parotitis) produces painful bilateral parotid swelling; the tightly bound capsule makes any swelling tense and tender.
Pleomorphic adenoma is the commonest parotid tumour, usually in the superficial lobe; superficial parotidectomy demands meticulous facial nerve preservation.
Frey's syndrome (gustatory sweating) follows parotid surgery when regenerating parasympathetic fibres misdirect to sweat glands of the overlying skin.
Auriculotemporal referred pain: parotid or temporomandibular joint pathology may present as earache.
A stone (sialolith) or stricture of Stensen's duct causes mealtime swelling; the duct orifice opposite the second upper molar should be inspected and milked during examination.

Study Points

List the three structures traversing the parotid in their superficial-to-deep order.
Trace the secretomotor pathway to the parotid and relate it to referred otalgia.
Know why the marginal mandibular branch is the branch most at risk in extraoral mandibular procedures.