Nerve Injuries / orthodontic courses by Indian dental academy

NERVE INJURIES AND ITS REPAIR

INDIAN DENTAL ACADEMY

Leader in continuing dental education www.indiandentalacademy.com

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INTRODUCTION

Nervous system performs the vital function of COMMUNICATION for the body

PRIMARY ORGANS

The brain spinal cord and The nerves

MAIN TYPES OF CELLS

2 Types,- Neuroglia: special connective tissue

cells of the nervous system Neurons: these are the (unit) nerve

NEUROGLIANumber: 900 billionTypes,-AstrocytesOligodendrogliaMicrogliaSchwann cells

ASTROCYTESAstron = star; kytos = cell.Star shapedMost numerous typeWebs of Astrocytes form tight sheaths around the brain’s capillaries. The tight junction between the endothelial cells that form brain capillary walls together constitute the “blood-brain barrier

MICROGLIA

Small, stationary cellsIn inflamed or degenerating brain tissue they enlarge, move about and carry on phagocytosis

OLIGODENDROGLIA

Smaller cells and have fewer processes than Astrocytes.They either lie clustered around nerve cell bodies or arranged in rows between nerve fibers in the brain and cord.Holds nerve fibers togetherProduces fatty myelin sheath over the fibers in the brain and cord

SCHWANN CELLSNot found in the brain and the cordFound in the peripheral nerves of the bodyThey function to form the,-

Neurilemma Myelin sheath

NEURONS

Number: 100 billionThese are the unit cells of the nervous systemforms the basic unit of the nerve fiber

CLASSIFICATION

According to the direction in which they conduct impulse:Afferent, efferent and interneurons.According to number of processes:Multipolar, bipolar and unipolar

AFFERENT/SENSORY NEURONS

Transmits nerve impulses to the spinal cord or brain

EFFERENT/MOTOR NEURON

They transmit nerve impulses away from the brain or spinal cord to or towards the muscles or glands

INTERNEURONS

They lie entirely in the central nervous systemThey conduct impulses from the afferent neurons toward efferent neurons

MULTIPOLAR NEURONS

Most of the neurons in the brain and spinal cord are multipolarThey have only 1 axon but several dendrites.

BIPOLAR NEURONS

Have one axon and one dendriteLeast typefound in, retina of eye, the spiral ganglion of the inner ear and the olfactory pathway

UNIPOLAR NEURONS

Originate in the embryo as bipolar neurons During course of development the 2 processes fuse for a short distance beyond the cell body.then they separate into clearly distinct axon and dendriteSensory neurons are mostly unipolar

STRUCTURE

Neurons consists of,Cell bodyAxon andDendrites

CELL BODY/SOMA/ PERIKARYON

Largest part of the nerve cellIn clusters cell bodies have gray colourAnd are known as nuclei in brain and spinal cord and ganglia elsewhereIt contains nucleus, cytoplasm and various organelles found in other cells

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Cytoplasm

A neurons cytoplasm extends through its cell body and its processes.A plasma membrane encloses the entire neuronstructures – dendrites, axons, neurofibrils, nissl bodies, myelin sheath and neurilemma are only found in the neurons

DENDRITES

Dendrites = tree in Greek terminal branches of the Multipolar neuronsDistal ends of sensory neurons are called as receptorsThey conduct impulses to the cell body of the neuron

single process extending from the cell body.Vary in length and diameterLength- max.a meter long; min.few mmDiameter- max. 20microns; min. 1micronDiameter directly proportional to velocity of conductionConducts impulse away from cell body.

Axons terminate in many branched filaments called telodendria and they contain numerous vesicles and mitochondria.

NEUROFIBRILS

These are very fine fibers extending through dendrites, cell bodies and axons.They consist of still thinner fibers microtubules and microfilaments.

NISSL BODIES

Consists of layers of small pieces of the endoplasmic reticulum with many ribosomes lying between them.They appear as large granules widely scattered through the cytoplasm of the cell body only.

specialized in protein synthesis.needed for maintaining and regenerating neuron processes and for renewing chemicals involved in the transmission of nerve impulses from one neuron to the other.

THE MYELIN SHEATH

A segmented wrapping of fatty substance around an axon called myelin.One segment of myelin sheath extends from one node of Ranvier to the next.One Schwann cell forms one segment of the myelin sheath around an axon located in a nerve .

A loop of Schwann cells plasma membrane pushes inwards towards the section of axon adjacent to it and wraps itself in a jelly-roll fashion around that section. this inward movement of the loop plasma membrane squeezes the rest of the cell in the outer direction to form neurilemma.

The several rolled up layers of the Schwann cells plasma membrane lying inside the neurilemma constitute the myelin sheath.

Fibers that have myelin sheath are called myelinated fibers and those that have only thin layer of myelin are called unmyelinated nerve fibers

A tract is a bundle of myelinated axons.The high fat content of myelin gives it a creamy white colour and make up the white matter of the brain and spinal cord.White matter found outside the brain and cord consists of nerves

NEURILEMMA/ SHEATH OF SCHWANN

a delicate outer covering around the axon located outside of the brain and cords in nerves and plays an essential part in the regeneration of cut and injured axons.Axons in the brain and cord have no neurilemma and hence don't regenerate.but those in nerves do.

EtiologyNerve injuries result from a variety of oral

and maxillofacial surgical procedures,such as,-Third molar odontectomyManagement of facial traumaOrthognathic surgeryEndosseous dental implant placement

Salivary duct and gland surgeryTreatment of benign and malignant lesions of the head and neckPreprosthetic surgery and Endodontic and periradicular surgery

CLASSIFICATION OF NERVE INJURY

SEDDONS CLASSIFICATION:(1943)NeuropraxiaAxonotmesisNeurotmesis

Neuropraxia:

Usually compression injury (mild)

Local conduction block & demyelination

Thick myelinated nerves mainly affected

Heals by repair of demyelination by Schwann cells, takes hours to several days

Axonotmesis:Usually after traction injury or severe compressionWallerian degeneration occurs Endoneurial tubes are intact & good sensory recovery but incomplete and takes several months.Limiting factor is the distance of regeneration required. Worse with proximal injuriesDeficit is severe paresthesia.

Neurotmesis:

Most severe, there is severance of the nerve.Sensory deficit is either anesthesia or dysesthesia.Intraosseous nerve injuries may exhibit some degree of sensory recovery as the canal acts as a guide.

SUNDERLAND CLASSIFICATION

Classified in the year 1951Accounts for the injuries between an Axonotmesis and Neurotmesis based on involvement of the perineurium

First degree injury:

Same as neuropraxiaAxonal conduction blockade as a result of ischemia or mechanical demyelination.Three types, type 1, 2 and 3

Type1: result of manipulation(mild traction or mild compression) seen in sagittal ramus osteotomy, lingual nerve manipulation during sialadenectomy.Conduction block due to interruption of segmental or epineurial blood vessels.Recovery within hours(24 hrs)

First degree type 2

Results from moderate manipulationConduction block due to intrafascicular edema from trauma to injure the endoneurial capillaries Recovery within a week with resolution of edema

First degree type 3Due to severe nerve manipulationSegmental demyelination seen,response is paresthesia.Recovery is complete with in 1 to 2 monthsSurgery not indicated in first degree unless there is a foreign body irritant

Second degree injurySecond ,third and fourth degree injuries overlap with Seddon’s axonotmesisThe axons are damaged and undergo degeneration and regeneration, rest nerve components remain intactGeneralized paresthesia with localized area of anesthesia is presentSurgical intervention not reqd.

Third degree injury

The intrafascicular tissue components, the axons and endoneurium are damagedRecovery is fair to poor with some degree of persistent paresthesia/synesthesia Surgical intervention dictated by the sensory disturbance,the recovery pattern,presence of foreign body and severity of injury

Fourth degree of injuryFascicular disruption with damage to axons endoneurium and perineuriumNeuropathic sensory impairment high due to extensive internal fibrosis Results in anesthesia,dysesthesia,synesthesia and severe paresthesiaSensory recovery is poorRequires surgical intervention

Fifth degree injury

Transection or rupture of the entire nerve trunkResults in loss of nerve conduction at level of injury & in distal nerve segment Recovery is poorBetter in intraosseous injury (if canal is intact). requires surgical adaptation & coaptation

Sixth degree injury

Added by Mackinnon & DellonIt’s a mixed combination of Sunderland's five degrees of injuryWithin the same nerve trunk some fascicles may exhibit normal function & others with varying degrees of nerve injuryPresents greatest challenge to the surgeon

Physiologic Conduction Block

Type ‘A’ conduction blockIs due to intraneural circulatory arrest or metabolic{ionic}blockNo nerve fiber pathologyImmediately reversible Improves with restoration of circulation to nerve trunk

Type ‘B’ conduction block Is due to intraneural edema resulting in increased endoneurial fluid pressure or metabolic blockLittle or no nerve fiber pathologyComplete recovery within days to weekImproves with decrease in edema and increased venous drainage

Symptomatic Classification

Based upon subjective complaints of numbness Broadly classified into:AnesthesiaParesthesiaDysesthesia

Anesthesia

Complete loss of any stimulus detection,stimulus localization or stimulus interpretation or perceptionAssociated with severe injury recovery slow & unpredictable Surgical intervention necessary

Paresthesia

Is an alteration in sensibility in which there is abnormal stimulus detection &stimulus perception that may be perceived as unpleasant but is not painful.

Stimulus{touch & pressure / pain} detection may be normal,increased {hyperesthesia / hyperalgesia}or decreased {hypoesthesia /hypoalgesia} & may affect either mechanoreception or nociception

These abnormalities are the result of conduction disturbances, ischemia &alterations in protein transport along the axon to the peripheral receptor & not necessarily from disruptions of the axonsDifficulty in quickly & accurately localizing the point of stimulus application is called synesthesis

It is probably the result of misdirection of axons during the process of regeneration and is common finding following neurorrhaphy Distal nerve atrophy is not a concern with paresthesias therefore there is no urgency for surgical exploration & repair

Dysesthesia

There is abnormal stimulus detection & stimulus perception that may be perceived as unpleasant and painful It is paresthesia with pain which may be spontaneous or triggered

Types of Dysesthesia

Allodynia,Hyperpathia(to pressure)These types are associated with neuromas,entrapment and sympathetically maintained pain and require surgical intervention.

Anatomic classification

Intraosseous nerve injurySoft tissue nerve injury

Histopathologic classification:

Neuromafibrosis

Pathophysiologic classification:CompressionCompartment syndromeStretch injuryTransection, laceration, rupture and avulsionChemical injuryNerve injection injuryAutonomically maintained painCentral neuropathy

Clinical Neurosensory Testing

McGill pain questionnaireVisual analog scale

Nonsurgical treatment

Treatment algorithms

Surgical treatment

ExposureExternal neurolysisInternal neurolysisNerve stump preparationApproximationCoaptation

External neurolysis

Internal neurolysisIt refers to surgical manipulation within the epineurium to prepare the nerve for repairTypes of internal neurolysisEpifascicular epineurotomyEpifascicular epineurectomyInterfascicular epineurectomy

Neurorrhaphy

Nerve graft

Entubulation techniques

Direct nerve repair

Cross face nerve grafting(faciofacial anastomoses)

Nerve crossovers

Regional muscle transposition

Free muscle grafts

Nerve-muscle pedicle technique

Microneurovascular Muscle Transfers

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Nerve Injuries / orthodontic courses by Indian dental academy

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