DENTIST NERVE

MOHAMMAD AKHEEL OMFS PG

The trigeminal nerve is so called because of its three main divisions i.e. the Ophthalmic, Maxillary & Mandibular nerves.

It is the largest of the cranial nerves.

It is the fifth cranial nerve

It is a mixed nerve.

It is sensory to the greater part of the scalp, the teeth, and the oral and nasal cavities.

Motor supply is to the MOM. Proprioceptive nerve fibres arise from the masticatory and extra-ocular muscles.

MOTOR ROOT

It arises separately from the sensory root in the motor nucleus of pons. At the semilunar ganglion it passes inferolaterally under the ganglion towards for.ovale, through which it leaves the middle cranial fossa along with the man.div. After it exits the skull, it unites with the sensory root and forms a single nerve trunk. It supplies the following muscles:

1. Muscles of mastication

2. Mylohyoid

3. Ant belly of the diagastric

4. Tensor tympani

5. Tensor veli palatini

SENSORY ROOT

The fibres of the sensory root arise from the cells of the trigeminal ganglion. The branches of the unipolar cells of the trigeminal ganglion are divided into central and peripheral branches. The central branches leave the

concave surface to enter the pons. The peripheral branches are grouped to form the ophthalmic and maxillary nerves and sensory part of the mandibular nerve.

 

THE TRIGEMINAL GANGLION

Sensory root fibres of the trigeminal nerve comprise the centralprocess of cells located in the trigeminal ganglion.2 ganglion ,one inervating each side of face.located in meckel’s cavity,on the anterior surface of the petrous portion of temporal bone.measures arprox. 1.0x2.0cm. It lies at depth of 4.5 –5 cm from the lateral aspect of the head near the posterior part of the zygomatic arch. It is cresentic or semilunar in shape. Medially it

is related to I.C.A & cavernous sinus, inferiorly with the motor root and the greater petrosal nerve & the apex of the petrous temporal bone and for.lacerum. Blood supply to the ganglion is through the

ganglionic branches of the ICA & the accesory meningeal artery which enters through the for.ovale.

Various nuclei associated with the fifth nerve are situated within the pons. They are:

1. Motor nucleus

2. Sensory nucleus

3. Mesencephalic nucleus

4. Spinal nucleus

  The 3 Main divisions of the trigeminal nerve are

V1 Opthalmic division.

V2 Maxillary division.

V3 Mandibular division.

OPTHALMIC NERVE

It is the superior division of the V nerve & is the smallest.

Leaves the cranium and enters the orbit through superior orbital fissure.

It is wholly sensory.

It has 3 branches. All 3 of them pass through the sup. orbital fissure into the orbit. They are;

1.Lacrimal nerve

2.Frontal nerve

3.Nasocilliary nerve

1. Lacrimal nerve: It is the smallest. It supplies the lacrimal gland & the conjuntiva. It pireces the orbital septum and ends in the skin of the upper eyelid.

2) Frontal nerve:

It is the largest branch & appears to be the direct continuation of the ophthalmic division. It enters the orbit through the SOF divides into 2 branches.

i. The supra orbital branch: It is larger & more laterally placed. It supplies the skin of the forehead & scalp as far back as the vertex. It also supplies the mucous membrane of the frontal sinus & pericranium

ii. The supra trochlear branch: It is smaller & more medially placed. It curves upward on the forehead , close to the bone. It supplies the skin of the upper eyelid & lower part of the forehead.

3) Nasocilliary nerve: It is intermediate in size & runs more deeply. Its branches are divided as following;

i. Branches in the Orbit

ii. Branches in the Nasal cavity

iii. Branches on the face

(I) Branches in the Orbit:

i. Long root of the cilliary ganglion: It is sensory & passes through the ganglion without synapsing and supplies the eyeball.

ii. Long ciliary nerve: Supplies the Iris & Cornea.

iii. Posterior ethmoidal nerve: It enters the post.ethmoidal canal & supplies to the mucous membrane lining of the Post. Etmoidal & Sphenoidal paranasal air cells.

iv. Anterior ethmoidal nerve: It supplies to the Ant.ethmoidal & frontal paranasal air cells. In the upper part of the nasal cavity, it further divides into:

1) Internal nasal branches: It has medial\septal branches to the septal membrane. It also has lateral branches, which supply the nasal conchae & the ant. nasal wall

2) External nasal branches: supplies the skin on the tip & ala of the nose.

 

2) Branches in the nasal cavity:

The branches arising here supply the mucous membrane of the nasal cavity.

3) Terminal branches on the face:

They supply sensory nerves to the skin of the medial parts of the both eyelids, the lacrimal sac. They also supply skin on the bridge of the nose.

MAXILLARY NERVE

This is the second & intermediate division of the trigeminal nerve.

It is wholly sensory.

Course: It begins at the middle of the trigeminal ganglion as a flattened, plexiform band, passes horizontally forwards along the lateral wall of the cavernous sinus. It leaves the skull through the foramen rotundum & becomes more cylindrical & firmer in texture.It crosses the upper part of the pterygopalatine fossa, inclines laterally on the posterior part of the orbital process of the maxilla & enters the orbit through the inferior orbital fissure.It is now termed as the infra orbital nerve. It passes through the infra orbital groove & canal in the floor of the orbit & appears on the face through the infra orbital foramen.

The branches of the maxillary nerve can be divided into the following 4 groups:

1) In the cranium: Meningeal

2) In the pterygopalatine fossa: Ganglionic, Zygomatic, Post.superior alveolar

3) In the infra orbital canal: Middle sup. alveolar,Anterior superior/ Greater alveolar

4) On the face: Palpebral, nasal, superior labial

I. Branch given off on the cranium

1. Meningeal branch: It is given off near the foramen rotundum. It supplies the duramater of the anterior & middle cranial fossae.

II. Branches in the pterygopalatine fossa.

1. The ganglionic branches: They connect the maxillary nerve to the pterygopalatine ganglion.They contain secretomotor fibres to the lacrimal gland. They provide sensory fibres to the orbital periosteum & mucous membrane of the nose, palate & pharynx.

2. The zygomatic nerve: It arises in the pterygopalatine fosssa from the maxillary nerve and travels anteriorly , entering through the inferior orbital fissure where it divides into 2 branches. The Zygomaticofacial nerve perforates the facial surfaces & supplies the skin over the zygomatic bone..

The Zygomaticotemporal nerve perforates the temporal surface of the zygomatic bone , pierces the temporalis fascia, & supplies the skin over the anterior temporal fossa region.

3. Posterior superior alveolar nerve: It begins in the pterygopalatine fossa but divides into 3 branches which emerge through the pterygomaxillary fissure.2 branches enter the posterior wall of the maxilla above the tuberosity & supply the 3 molar teeth(except the mesiobuccal root of first molar). The third branch pierces the buccinator & supplies the adjoining part of the gingiva & cheek along the buccal side of the upper molar teeth.

III. Branches in the Infraorbital canal( Infraorbital nerve)

1. Middle superior alveolar nerve: It arises from the Infra orbital nerve & runs downwards & forwards along the infraorbital groove along the lateral wall of the maxillary sinus. It divides into branches which supply the maxillary premolars & mesiobuccal root of the first molar teeth.

2. Anterior superior alveolar nerve: It also arises in the infraorbital canal near the mid point. It runs in the anterior wall of the maxillary antrum. It runs inferiorly & divides into the branches, which supply the canine & incisors. A nasal branch from this nerve, given off from the superior dental plexus supplies the mucous membrane of the anterior part of the lateral wall & floor of the nasal cavity. It ends in the nasal septum.

IV. Branches given on the face:

1. The palpebral branches: They arise deep to the orbicularis oculi & pierce the muscle, supplying the skin over the lower eyelid& lateral angle of the eye along with the Zygomaticofacial & Facial nerves.

2. The nasal branches: They supply the skin of the nose & tip of the nasal septum & join the External nasal branch of the anterior ethmoidal nerve.

3. The superior labial branches: These are large & numerous. They supply the skin over the anterior part of the cheek & upper lip including the mucous membrane & labial glands. They are joined by the facial nerve & form the infraorbital plexus.

 

Sphenopalatine\Pterygopalatine ganglion

  It is the largest of the peripheral ganglia.

It is associated with the greater petrosal nerve. ( Functionally it is part of the Facial nerve). It acts as a

relay staion b\n the superior salivatory nucleus in the pons and the lacrimal gland & mucous & serous glands of the palate, nose & paranasal sinuses.

It lies in the pterygopalatine fossa, suspended from the maxillary division of the trigeminal nerve by 2 roots just

in front of the opening of the pterygoid canal.Branches arise from the maxillary nerve through its ganglionic branches. They do not establish any sympathetic connections with its cells. The branches are: -

The branches of the Pterygopalatine ganglion are:-

I. Orbital branches:

II.Palatine branches:

1.Anterior/greater palatine

2.Middle palatine

3.Posterior palatine

III.Nasal branches:

1.Posterior superior lateral

2.Nasopalatine/Sphenopalatine

IV.Pharyngeal branch:

1. Orbital branches:

They are made up of afferent fibres & convey sensory impulses from the periosteum of the orbit. Others supply the mucous membrane of the Posterior ethmoidal & sphenoidal air cells.

2. Palatine branches:

They are distributed to the roof of the mouth, soft palate, tonsil & lining membrane of the nasal cavity. It gives of three branches. They are:-

Palatine branches:- continued

i. Greater palatine nerve: it emerges from the foramen medial to the 3 rd molar, continues forward splitting into

number of branches. It is sensory to the mucosa of the hard palate & palatal gingiva.

ii. Middle palatine nerve: This nerve emerges from a small foramen in the medial aspect of the pyramidal part of the palatine bone. Sensory supply is to the mucous membrane of the soft palate. 

iii. Posterior palatine nerve: It emerges from a foramen slightly lateral to the median palatine nerve. It contains

sensory & secretomotor fibres to the mucous membrane of the Tonsillar area.

3. Nasal branches:

i. Posterior superior lateral nerves: they supply they posterior part of the nasal conchae

ii. Nasopalatine(Sphenopalatine) nerve: It passes downwards & forwards between the periosteum &mucous membrane in the region of the vomer, continues downwards & forwards, reachs the floor of the nasal cavity.Descends into the incisal canal to appear in the anterior part of the hard palate & supplies the mucous membrane of the premaxilla.

4.Pharyngeal branches:

This branch supplies sensory & secretory fibers to the mucous membrane of the nasopharynx. It arises from passes through the palatovaginal canal along with the pharyngeal branch of the maxillary artery.

MANDIBULAR NERVE

It is the third & largest division of the trigeminal nerve.It is made up of 2 roots: a large sensory root which proceeds from the lateral part of the trigeminal ganglion & almost immediately emerges out through the foramen ovale & a small motor root which passes below the ganglion, & unites with the sensory root just outside the foramen.

Immediately beyond the junction of the 2 roots, the nerve sends off the meningeal branch & the nerve to the medial pterygoid. Now the main trunk divides into a small

anterior & a large posterior trunk.

As it descends from the foramen, the mandibular nerve lies at a distance of 4 cm from the surface & a little in front of the neck of the mandible.

The braches of the Mandibular nerve:-

I. Branches of the undivided nerve.

i. Meningeal branch/nervus spinosus.

ii. Nerve to the medial pterygoid

II. Branches of the divided nerve:

(A) Anterior division: (B) Posterior division:

1.Buccal nerve 1. Auriculotemporal nerve

2.Massetric nerve 2.Lingual nerve

3.Deep temporal nerve 3.Inferior alveolar nerve

4.Nerve to the lateral pterygoid.

 

BRANCHES OF THE UNDIVIDED NERVE

1.Meningeal nerve:

It enters the skull through the foramen spinosum along with MMA.

It has anterior & posterior divisions that supply the dura of the middle & anterior cranial fossae.

2. Nerve to the medial pterygoid:

It is a slender branch that supplies to the deep surface of the muscle.

It also gives 1-2 filaments to the tensor tympani & the tensor veli palati muscles.

 

BRANCHES OF THE DIVIDED NERVE

I. Anterior division

1.The buccal nerve:

It passes between the 2 heads of the lateral pterygoid & descends beneath or through the temporalis. It emerges

from under cover of the ramus & ant. border of the masseter & unites with the buccal branches of he facial nerve.

It supplies the skin over the ant. part of the buccinator & mucous membrane lining the buccal surface of the gum.

2.The massetric nerve:

~Passes laterally above the lateral pterygoid in front of the TMJ & behind the tendon of

temporalis.

~It passes through the mandibular notch to sink into the masseter muscle.

~It also gives a branch to the TMJ.

3.The deep temporal nerves:

~They are 2 in number.

~They pass above the upper head of the lateral pterygoid, turn above the infra temporal crest & sink into the deep part of the temporalis muscle.

4.The nerve to the lateral pterygoid.

~These are 2 in number; one supplying each muscle head.

II.Posterior Division

1.The Auriculotemporal nerve:

Course of the nerve

} The auriculotemporal nerve arises by a medial & lateral roots, that enclircle the MMA & unite behind it just below the foramen spinosum.

} The united nerve passes backwards, deep to the lateral pterygoid muscle & passes between the

sphenomandibular ligament & the neck of the condyle.

} It then passes laterally behind the TMJ i.r.t. to the upper part of the parotid. It emerges from behind the TMJ, ascends posterior to the superficial temporal vessels & crosses the posterior root of the zygomatic arch.

 

Branches of the Auriculotemporal nerve:

1. Parotid branches-----secretomotor, vasomotor.

2. Articular branches--- to the TMJ.

3. Auricular branches---to the skin of the helix & tragus.

4. Meatal branches----- Meatus of the tymphanic membrane

5. Terminal branches----Scalp over the temporal region

 

Lingual nerve

~It lies between the ramus of the mandible & the muscle in the pterygomandibular space.

~It then passes deep to reach the side of the tongue. Here it lies in the lateral lingual sulcus against the deep surface of the mandible on the medial side of the roots of the third molar tooth where it is covered only by mucous membrane of the gum.

~From here it passes on to the side of the the side of the tongue where it is crosses the styloglossus & runs on the lateral surface of the hyoglossus & deep to the mylohyoid in close relation to the deep part of the submandibular gland &its duct.

~It gives off sensory fibres to the tonsil & the mucous membrane of the posterior part of the oral cavity.

Communication of the facial nerve (Chorda

tymphani) with the lingual nerve.

As the lingual nerve passes medially to the lateral

pterygoid, it is joined from behind by the chorda

tympani. This nerve conveys secretory fibres from the

facial nerve. The parasympathetic secretory fibres control

the submandibular & sublingual salivary glands.

Inferior alveolar nerve.

~It is the largest terminal branch of the posterior division of the mandibular nerve.

~The nerve descends deeep to the lateral pterygoid muscle at the lower border of the muscle, it passes b/n the sphenomandibular ligament & the ramus to enter the mandibular foramen.

~In the canal the nerve runs alongside the inferior alveolar artery as far as the mental foramen where it emerges out& gives off the mental & incisive branches.

~From here the nerve runs in the canal giving of branches to the mandibular teeth as apical fibres & enters the apical foramena of the teeth to supply mainly the pulp as well as the periodontium.

Branches of the nerve :-

1. Mental nerve: it supplies to the skin of the chin & the mucous membrane as well as the skin of the lower lip.

2. Incisive branch: continues anteriorly from the mental nerve in the body of the mandible to form the incisive plexus & supplies the canine & incisors.

3. Mylohyoid nerve: it is given of before the nerve enters the canal & contains both sensory & motor fibres.It pierces the sphenomandibular ligament, descends in a groove in the medial side of the ramus & passes beneath the mylohyoid line supplying the mylohyoid muscle as well as the anterior belly of the digastric.

 

Submandibular ganglion:

It is a small ovoid body that is suspended from the lingual nerve above the submandibulat salivary gland. The preganglionic parasympathetic fibres reach the ganglion arising from the superior salivatory nucleus, reaching through the facial, chorda tympani & the lingual nerve. Post ganglionic fibres are conveyed through the submandibular, sublingual & anterior lingual salivary glands.

The sensory nerves reach the ganglion through the lingual nerve.

Sympathetic fibres are derived from the plexus around the facial artery & contain post ganglionic fibres arising in the superior cervical ganglion. They provide

secretomotor fibres to the submandibular & sublingual glands.

Otic ganglion

It is a flattened ovoid body located on the medial side of the undivided nerve. It is situated below the foramen ovale & the MMA. It has 2 main roots:-

1.Parasympathetic preganglionic (secretory) fibres: they arise from the inferior salivatory nucleus.The

efferent fibres pass by way of the glossopharyngeal nerve through the jugular canal.Below the canal it passes through the tympanic branch of the glossopharyngeal nerve( Jacobson’s nerve), passing through the tympanic plexus & the lesser petrosal branch to reach the Ganglion. (the lesser superficial petrosal nerve is the parasympathetic root of the otic ganglion) The postganglionic fibres pass through the auriculotemporal

nerve.

 

2.Sympathetic root: It is made up of the postganglionic fibres that have originated in the superior cervical sympathetic ganglion & the plexus of the MMA. The fibres pass through the ganglion uninterrupted. These fibres reach the parotid thru the auriculotemporal nerve.

Afferent of sensory nerves come from the parotid through the auriculotenporal nerve.

GENRAL CONSIDERATIONS OF TRIGEMINAL NERVE.

Damage to the trigeminal nerve as a complication of surgery

Cancer surgeries: the tendency of squamous cell carcinoma to affect the cutaneous branches places these nerves at risk for injury during surgery. Similarly the tendency of salivary gland tumors (ACC) to spread along perinueral spaces.

The ophthalmic branches( frontal, SO, ST, lacrimal & nasal) can be injured during eye brow surgeries. All patients in whom coronal incision was made complained of forehead numbness & paresthesias.

Paresthesias of the upper lip, gums & teeth are a common complication of transantral procedures.

Risk of damage to the lingual nerve is to be anticipated during procedures like removal of impacted third

molars, submandibular gland surgeries etc..

Trigeminal nueralgia:

It is a paroxysmal, intermittant,excruciating pain confined to one of the branches of the trigeminal nerve.

Characterised by unilateral affliction, not crossing the midline, presence of trigger zones, cessation of pain during sleep.

The etiology is not definitely known. Suggested causes are viral lesions of the ganglion, demyelination of the nerves, narrowing of the foramina & Idiopathic.

Diagnosis: Based on C/f s & diagnostic test block on the trigger zones.

Treatment modalities include..

1. Carbamazepine(Tegretol) 100 mg od, bd or tid, depending on the severity or frequency of pain.

2. Injection of 60 to 90% alcohol in the nerve trunk or ganglion.

3. Peripheral nuerectomy or cryotherapy of the peripheral trigger zone.

4. Peripheral radiofrequency thermolysis & radiofrequency thermogangliolysis.

5. Microvascular nerve root decompression procedure. It is a nuerosurgical procedure wherein the internal vascular loops of the superior cerebellar artery is made to compess on the trigeminal nerve root.

Mental nerve nueralgia.

Due to resorption of the lower alveolar ridge, the borders of the denture flange may compress on the mental nerve, causing pain. Radiologically, the foramen can be seen at the level of the surface of the ridge. Shifting the foramen down is the treatment of choice.

Similar pain is felt due to narrowing of the foramen. Decompession of the nerve by carefully enlargening the foramen is the treatment of choice.