facial nerve

FACIAL NERVE

Anatomy Nuclei Course Branches and distribution Ganglia Blood supply

Functional ComponentsFunctions of the Facial NerveClinical Examination of the Facial NervePathology of the Facial Nerve Importance of facial nerve in operative dentistryEndodontic implications of facial nerveConclusion

CONTENTS

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NerveSympatheticParasympatheticNeuronNucleiMotor/Efferent (Brachial, visceral)Sensory/Afferent (General, special)Upper motor neuronLower Motor neuronParesis Plegia

Key terms:

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ANATOMY

• 7th Cranial

nerve

• Mixed nerve

• Nerve of the

hyoid arch

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NUCLEI

• Four nuclei -

Motor nucleus (branchiomotor)

Superior salivatory nucleus (parasympathetic)

Lacrimatory nucleus (parasympathetic)

Nucleus of tractus solitarius (gustatory)

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Nerve innervation by the Motor Nucleus in the upper and lower part of the face

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Origin

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Relationship of the cranial nerves in the internal acoustic meatus

VIII

VII (m)

Labrynthine vessels

Dura

Arachnoid

Nervus intermedius

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INTRACRANIAL COURSE

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DISTRIBUTION OF FACIAL NERVE WITHIN THE TEMPORAL BONE

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Stylomastoid Foramen

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EXTRACRANIAL COURSE

Within the facial canal

At its exit from the stylomastoid foramen

Terminal branches within the parotid gland

Communicating branches with adjacent cranial and spinal nerves

Branches and Distribution

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BRANCHES AND DISTRIBUTIONWithin the facial canal

1. Greater Petrosal Nerve

2. Nerve to the stapedius muscle

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3. Chorda Tympani Nerve

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COURSE OF CHORDA TYMPANI NERVE

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Tongue

Sublingual

gland

Submandibular Gland

Submandibular Ganglion

Lingual nerve

carrying general

sensation

Chorda tympani

taste fibre

Chorda tympani Secretomotor

fibre (preganglionic)

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At its exit from the stylomastoid foramen1. Posterior auricular 2. Digastric 3. Stylohyoid

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Terminal branches within the parotid gland

CervicalMandibular

Buccal

Zygomatic

Temporal

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Anatomic Variations

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   In the internal acoustic meatus - With the acoustic nerve at the

geniculate ganglion

With the sphenopalatine ganglion by the greater superficial petrosal nerve.

With the otic ganglion by a branch which joins the lesser superficial petrosal nerve.

In the facial canal - With the auricular branch of the vagus.

At its exit from the stylomastoid foramen - With the glossopharyngeal.

On the face - With the trigeminal.

In the neck - With the cutaneous cervical.   

Branches of Communication

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Ganglia Of The Facial Nerve

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The facial nerve derives both an intrinsic and an extrinsic blood supply.

Intrinsic – middle cerebral artery

Extrinsic - the stylomastoid

artery the middle

meningeal artery the anterior

cerebellar artery

Blood supply of the Facial Nerve

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Functional Components1. Branchial

Motor

2. Visceral Motor

3. Special Sensory

4. General Sensory

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Clinical Examination of the Facial NerveMotor Examination

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Testing Taste

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Corneal Reflex

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Sucking Reflex

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EFFERENT FUNCTION

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AFFERENT FUNCTION

04/08/2023 34Review Article The receptors and cells for mammalian taste Nature 444, 288-294 (16 November 2006)

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Physiology of Nerve injury

Sunderland's classification – five degrees Neuropraxia – 1st degree Axonotmesis – 2nd degree Endoneurotmesis – 3rd degree Perineurotmesis – 4th degree Neurotmesis – 5th degree

Pathology

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Facial paralysis is a dysfunction of the facial nerve that results in inability to control facial muscles on the affected side.

Facial Palsy

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Congenital/Acquired

Brain or parotid gland tumours

Trauma

Stroke

Lyme disease

Latent virus reactivation of zoster and Epstein Barr

Idiopathic – Bell’s Palsy

Causes

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I - Normal facial movements; No synkinesis

II - Slight Mild deformity, mild synkinesis, good forehead function, slight asymmetry

III - Moderate Obvious facial weakness, forehead motion present, good eye closure, asymmetry, Bell's phenomenon present

IV - Moderately Obvious weakness, increasing synkinesis; no forehead motion

V - Severe Very obvious facial paralysis, some tone present, cannot close eye

VI - Total Complete facial paralysis, absent tone

Grade Of Facial Paralysis House - Brackmann score

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Paralysis involving all divisions of the facial nerve is peripheral and that sparing the forehead is central.

Central versus Peripheral Paralysis

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Central Seven

It usually results from damage to upper motor neurons of the facial nerve.

Most commonly occurs due to stroke.

Central Facial Palsy

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Named after Scottish anatomist Charles Bell

Idiopathic, unilateral, self-limiting facial palsy

Infranuclear/lower motor type

Persistent latent viral infection activation, exposure to cold

Facial drooping on the affected side

Bell’s Palsy

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As a result of inflammation of the facial nerve, pressure is produced on the nerve where it exits the skull within its bony canal, blocking the transmission of neural signals or damaging the nerve.

Pathology

SymptomsClassic presentation – weakness on one side

of faceAwareness – drooling after brushing teeth or

drinking, asymmetry

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Signs

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BELL’S PHENOMENON

INFRANUCLEAR (LMN):a. Lesion at or below stylomastoid foramen – loss of facial expression on the same side as the lesionb. Lesion in the facial canal (lower level)– a + loss of taste sensation in anterior 2/3 rds of tongue and salivationc. Lesion in the facial canal (higher level) – a + b + loss of hearingd. Lesion at genu/proximal to genuculate ganglion – a + b + c + loss of lacrimation

Level of the lesion and the corresponding symptoms

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NUCLEAR LESION (LMN):Lesion in pons – unilateral facial palsy (6th nerve involvement also seen)

+ Contralateral pyramidal

signs (Millard Gubler syndrome)

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SUPRANUCLEAR LESION (UMN) :Contralateral lower side of face involved (voluntary movement) facial expressions

+Unilateral pyramidal signs (UMN type)

(Hemiplegia)

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Bell's palsy is a diagnosis of exclusion.

Lyme disease

Tumours (e.g., Acoustic neuroma , parotid gland tumours)

Ramsay Hunt syndrome

Demyelinating lesions

Sarcoidosis

Differential Diagnosis

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Heerfordt's syndrome

Melkersson-Rosenthal syndrome

Gustatory tearing or crocodile tears

Syndromes associated with Bell’s Palsy

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Guillain-Barré syndrome

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Moebius Syndrome

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Ramsay Hunt Syndrome

Eye care

Oral steroid – Prednisone 1 mg/kg/day for 10-14 days

Surgery to relieve pressure on the nerve

Local superficial heat therapy (i.e. hot pack or infrared rays) for 15min/session (Europa Medicophys 2006;42:41-7)

Physiotherapy (Physiotherapy treatment of Bell's palsy: a case report New Zealand Journal of

Physiotherapy, Nov, 2006 by James M. Elliott )

Facial muscle protection

Treatment

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Described by Gowers in 1884

A neurological disorder wherein blood vessels constrict the facial nerve causing facial spasm.

First symptom - intermittent twitching of the eyelid muscle leading to forced closure of the eye.

Hemifacial Spasm

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YouTube- HemiFacialSpasm before amp after.flv

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Treatment Medications -

carbamazepine, phenytoin and gabapentin

Injection of botulinum toxin type A

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Microvascular Decompression

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Trauma – Petrous bone fracture Surgery of middle ear,

mastoidectomy, parotid glandTumours – Neuroma/schwanoma

Meningioma Hemangioma Metastasis Osteopetrosis

FACIAL NERVE TRAUMA AND TUMOURS

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The transient loss of motor function of the orofacial muscles can hamper the smile line evaluation, an important parameter for restorative and prosthetic dentistry approaches.Chiche G, Pinault A. Esthetics of anterior fixed prosthodontics. Chicago: Quintessence, 1994.

IMPORTANCE OF FACIAL NERVE IN OPERATIVE DENTISTRY

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Released and ionized mercury can be taken up by tissues and nerves beneath fillings and in root canals.

Current animal experiments show that mercury is taken up by nerve endings and is transported towards the central nervous system in the same way as lead (Baruah, 1981).

When the amalgam fillings in the right part of the lower jaw were removed, the painful strain after the facial paralysis, present four years, disappeared. It seems close at hand to suspect a combination of the general poisoning and the mercury source in the two teeth in the lower jaw as primary causes of the nerve inflammation, resulting in the face paralysis on the same side.

Mercury Poisoning From Dental Amalgam Jaro Pleva, Ph.D.1

Orthomolecular Psychiatry, volume 12, Number 3, 1983 Pp. 184-193

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Neurological complications following extrusion of sodium hypochlorite solution into the facial soft tissues during root canal treatment International Endodontic Journal, 38, 843–848, 2005

Neurological sequelae can follow inadvertent hypochlorite extrusion.

Early recognition may avert a potentially more serious outcome.

Active hospital treatment including intravenous steroids and antibiotics is recommended.

Permanent mimic musculature and nerve damage caused by sodium hypochlorite: a case report. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2008 Sep;106(3):e80-3. Epub 2008 Jul 7

ENDODONTIC IMPLICATIONS OF FACIAL NERVE

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CASE REPORT - 1

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CASE REPORT - 2

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Transient facial nerve paralysis – introduction of LA into the

capsule of the parotid gland during IANB or Vazirani – Akinosi nerve block

Problem

Prevention

Management

Facial nerve palsy following intra-oral surgery performed with local anaesthesia

J.R.Coll.Surg.Edinb., 45,October 2000, 330-333

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7th cranial nerveBranches

Within facial At the stylomastoid On the faceCommunicating

canal foramen Branches

1. Greater 1. Posterior 1. Temporal

petrosal auricular 2. Zygomatic

2. Nerve to 2. Digastric 3. Buccal

Stapedius 3. Stylohyoid 4. Mandibular

3. Chorda 5. Cervical

tympani

Summary

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“The most important thing you wear is the expression on your face.”

Certain cases of facial nerve palsy following dental or maxillofacial procedures occur.

Prevention is better than cure.

CONCLUSION

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B.D. Chaurasia’s Human Anatomy vol 3

The Facial Nerve, Mark May Barry M. Schaitkin - 2000

Handbook of Local Anesthesia 5th edition

The facial nerve: anatomy and common pathology Semin Ultrasound CT MR. 2002 Jun;23(3):202-17

International Endodontic Journal, 38, 843–848, 2005

Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2008

Sep;106(3):e80-3. Epub 2008 Jul 7

Chiche G, Pinault A. Esthetics of anterior fixed prosthodontics. Chicago: Quintessence, 1994.

Mercury Poisoning From Dental Amalgam Jaro Pleva, Ph.D.1

Orthomolecular Psychiatry, volume 12, Number 3, 1983 Pp. 184-193

Color Atlas of neuroscience: Neuroanatomy and Neurophysiology by Ben Greenstein, Adam Greenstein

Neurological Classics

 By Robert H. Wilkins, Robert Wilkins, Irwin Brody

REFERENCES

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Thank you