Anatomy and functional significance
The trigeminal nerve (nervus trigeminus, cranial nerve V) is a mixed nerve. It originates from the trigeminal (gasserian) ganglion and exits the cranial cavity via three major trunks.
- First branch (ophthalmic nerve): exits through the superior orbital fissure.
- Second branch (maxillary nerve): passes through the foramen rotundum and the infraorbital canal.
- Third branch (mandibular nerve): leaves the cranium through the foramen ovale and enters the mandibular canal.
The first two branches provide exclusively sensory innervation to the facial tissues. The third branch contains not only sensory but also motor fibers (for the muscles of mastication), as well as specific gustatory fibers running to the anterior third of the tongue.
Classification and etiology
The condition is typically divided into two broad groups depending on the level of the lesion.
Idiopathic (peripheral) neuralgia is associated with damage to the peripheral branches. Its development is promoted by congenital or acquired narrowing of bone canals, jaw trauma, and dental factors: traumatic tooth extraction, extrusion of sealing material beyond the root apex into the mandibular canal, malocclusion, or galvanism phenomena due to metal prostheses. Psychological trauma plays a major role, particularly in women aged 40–60 years.
Symptomatic (central) neuralgia is caused by damage to the nerve trunk in the central structures. It is based on scarring and morphological changes following neuroinfections (meningitis, encephalitis, arachnoiditis), traumatic brain injuries, vascular disorders, and brain tumors.
Clinical presentation
A classic pain attack is short-lived — lasting from a few seconds to a couple of minutes. The pain is tearing, cutting, or stabbing in nature. It is frequently accompanied by reflex spasm of the facial muscles on the affected side.
The pain syndrome can be triggered by any external stimulus: a light touch to the skin, shaving, a gust of wind. Palpation reveals sharp tenderness at Valleix points (in the region of the infraorbital or mental foramina). The attack is frequently accompanied by pronounced autonomic reactions: skin and conjunctival hyperemia, tissue edema, rhinorrhea, lacrimation, and hypersalivation.
Motor function disorders
Damage to the motor portion of the third branch leads to dysfunction of the masticatory muscles.
The irritation syndrome manifests as trismus — a severe spasm of the masseter and temporal muscles. The jaws are tightly clenched, making eating impossible and impairing speech and respiration. When paresis or paralysis develops, asymmetry occurs: if the process is unilateral, opening the mouth causes the mandible to shift toward the affected side, and muscular atrophy develops over time. In bilateral paralysis, the jaw hangs open.
Specific forms of peripheral neuralgia
Several specific syndromes are distinguished in dental neurology:
- Dental plexalgia (alveolalgia): characterized by constant pain in the gingival area that worsens with weather changes, stress, or hypothermia.
- Postherpetic neuralgia: develops after a viral infection. Unlike the classic form, trigger zones are absent here, but small herpetic vesicles appear on the skin, accompanied by edema and severe itching.
- Ciliary ganglion involvement (Oppenheim's syndrome): attacks of sharp pain last from half an hour to several hours, localized behind the eyeball and accompanied by photophobia.
Briefly: answers to topical questions
Where is the trigeminal (gasserian) ganglion anatomically located?
The trigeminal (gasserian) ganglion (ganglion trigeminale) is located at the base of the skull. It lies above the apex of the petrous part (pyramid) of the temporal bone in a special trigeminal impression (impressio trigeminalis) on its anterior surface. Topographically, the ganglion lies lateral to the posterolateral part of the cavernous sinus and is adjacent to it posteriorly.
Specifically which muscles are innervated by the motor portion of the mandibular nerve?
The motor portion of the mandibular nerve innervates the muscles of mastication. The innervated muscles include:
- Masseter muscle — mentioned in the description of spasms and atrophy.
- Temporalis muscle — undergoes severe contraction (trismus) and atrophy in lesions.
- Pterygoid muscles — receive branches before the nerve enters the mandibular canal.
- Mylohyoid muscle (m. mylohyoideus) — innervated by the motor nerve of the same name.
- Digastric muscle — its anterior belly is innervated by a branch of the mylohyoid nerve.
What branches does the maxillary nerve give off along its course?
Along its course, the maxillary nerve (n. maxillaris) gives off the following branches:
- Zygomatic nerve — branches off directly near the foramen rotundum.
- Pterygopalatine nerves (nn. pterygopalatini) — branch off to the pterygopalatine ganglion (from which the nasopalatine, greater, and lesser palatine nerves arise).
- Posterior superior alveolar nerves (nn. alveolares superiores posteriores) — branch off in the pterygopalatine fossa after entering the infraorbital sulcus.
- Infraorbital nerve (n. infraorbitalis) — is the terminal branch that exits through the infraorbital foramen and forms the branches of the lesser "goose's foot".
Where on the face are all three Valleix points (exit points of the trigeminal nerve branches) projected?
The Valleix points (exit points of the trigeminal nerve branches) are projected on the face along a vertical line passing through the border of the inner and middle thirds of the supraorbital margin:
- First branch (n. ophthalmicus) — projected 0.5 cm above and lateral to the notch on the superior orbital margin (at the level of the supraorbital margin).
- Second branch (n. maxillaris) — projected 0.5–0.8 cm (or 0.5–0.75 cm) inferior to the notch on the inferior orbital margin.
- Third branch (n. mandibularis) — projected at the midpoint of the distance between the alveolar and inferior margins of the mandible (stepping upwards from the mandibular margin by 0.75 cm, at the midpoint of the distance from the intersection of the masseter muscle with the mandibular margin to the midline).
Which drugs are first-line for the medical treatment of trigeminal neuralgia?
Basic drug therapy for trigeminal neuralgia consists of anticonvulsants:
- Carbamazepine (finlepsin)
- Phenytoin
- Stasepin
- Baclofen
Periodic rotation of medications is necessary during treatment.
To remember the function of the third branch, the phrase is used: "The third branch is a hard worker." Out of all three trunks, only it contains motor fibers that make the masticatory muscles work.
Class and exam questions
Why are the conjunctival and corneal reflexes evaluated during the examination?
These reflexes help to verify the integrity of the reflex arc involving the sensory fibers of the V nerve.
Why do patients with neuralgia sometimes insist on extracting healthy teeth?
Intense pain attacks are frequently preceded by prodromal symptoms in the form of paresthesia in the teeth or jaws, causing patients to mistakenly mistake neuralgia for pulpitis or periodontitis.
How to distinguish postherpetic neuralgia from classical neuralgia?
In the postherpetic form, there are no characteristic trigger points, the pain is burning in nature, and small vesicles appear on the skin of half the face.
What else to study on this topic
- Differential diagnosis with alveolitis and acute pulpitis
- Technique for electroodontometry and rheography
- Symptoms of facial nerve palsy (lagophthalmos, Bell's phenomenon)
- Features and clinical presentation of glossopharyngeal neuralgia
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