Dentin

DENTINDr. Nithin Mathew

Dr. Nithin Mathew - Dentin

CONTENTS

Introduction Stages of tooth development Structure of dentin

Dentinal tubulesPeritubular dentinIntertubular dentinPredentinPrimary dentinSecondary dentinTertiary dentinInterglobular dentinGranular layer 2


Incremental linesOdontoblastic processes

PropertiesPhysicalChemical

Innevervation of dentin Theories of pain transmission

Direct neural stimulation theoryTransduction theoryHydrodynamic theory 3


Age & functional changesVitality of dentinDead tractsSclerotic dentin/ transparent dentin

Clinical considerationsConclusionReferences

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INTRODUCTION

Second layer of the tooth

Structure that provides the bulk and general form ofthe tooth

Since it begins to form slightly before the enamel, itdetermines the shape of the crown, including the cuspsand ridges and also the number and size of the roots.

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Physically and chemically, it closely resembles bone

Said to be a living tissue since the tubules present in itcontains processes of specialised cells, theodontoblasts.

Main morphologic difference between bone and dentinis that some of the osteoblasts exists on the surface ofthe bone and when one of the cells becomes enclosedwithin its matrix, it is called an osteocyte.

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But the odontoblasts cell bodies remain external todentin, but their processes exist within tubules indentin.

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STAGES OF TOOTH DEVELOPMENT

Teeth develop in distinct stages that are easilyrecognizable at the microscopic level.

Hence, stages of tooth development(odontogenesis) are described by the histologicappearance of the tooth organ.

The stages are described as the lamina bud,cap, early bell and late bell stages of toothdevelopment. 8


LAMINA STAGE

First morphologic sign of tooth development

Visible at approximately 6th week of humandevelopment.

At this stage, the cells in the dental epitheliumand the underlying ectomesenchyme are dividingat different rates, the latter more rapidly.

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The dental lamina has the full potential to inducetooth formation by dictating the fate of theunderlying ectomesenchyme.

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a : Nasal Septumb : Tonguec : Palatal Processesd : Dental lamina


BUD STAGE

The dental lamina continues to grow and thicken toform a bud

Cells of the ectomesenchyme proliferate andcondense to form the dental papilla.

At this stage, the inductive or tooth formingpotential is transferred from the dentalepithelium to the dental papilla.

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A : Ectodermal outgrowthB : Dental MesenchymeC : TongueD : Oral Cavity SpaceE : Oral Ecotoderm


CAP STAGE

The tooth bud assumes the shape of a cap that issurrounded by the dental papilla.

Ectodermal compartment of the tooth organ isreferred to as the dental or enamel organ.

The enamel organ and dental papilla becomeencapsulated by another layer of ectomesenchymalcells, called the dental follicle

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Separates the tooth organpapilla from the otherconnective tissues of thejaws.

Important step in toothdevelopment, because itmarks the onset of crownformation.

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a : Outer Dental Epitheliumb : Inner Dental Epitheliumc : Stellate Reticulumd : Dental Papillae : Dental lamina


EARLY BELL STAGE Dental organ assumes the shape of a bell as cells

continue to divide but at differential rates.

A single layer of cuboidal cells called the external orouter dental epithelium, lines the periphery of thedental organ

Cells that border the dental papilla and are columnarin appearance form the internal or inner dentalepithelium.

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The inner epithelium gives rise to the ameloblasts,cells responsible for enamel formation.

These cells secrete high levels of alkaline phosphatase.

In the region of the apical end of the tooth organ, theinternal and external dental epithelial layers meet at ajunction called the cervical loop.

These extends apically to form the HertwigsEpitheial root sheath which forms the root dentin

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Early Bell stage

Each layer of the dental organ has assumedseveral functions.

The reciprocal exchange of molecular informationbetween the dental organ and dental papillainfluences the important events that lead to celldifferentiation at the late bell stage.

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LATE BELL STAGE

The dental lamina that connectsthe tooth organ to the oralepithelium gradually disintegratesat the late bell stage.

Cells of the internal dental epithelium continue todivide at different rates to determine the precise shapeof the crown.

Shortly after, cells of the internal dental epithelium atthe sites of the future cuspal tips stop dividing andassume a columnar shape. 20


In summary, development of the tooth rudimentfrom the lamina to the late bell stages culminatesin the formation of the tooth crown.

As root formation proceeds, epithelial cells fromthe cervical loop proliferate apically andinfluence the differentiation of odontoblasts fromthe dental papilla as well as cementoblasts fromthe follicle mesenchyme.

This leads to the deposition ofroot dentin and cementum.

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a : Nerve Bundleb : Alveolar Bonec : Vasculatured : Oral Ectoderme : Tongue

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STRUCTURE OF DENTIN

The dentinal matrix of collagen fibres are arranged ina network.

As dentin calcifies, the HA crystals mask the collagenfibres

The bodies of odontoblasts are arranged in a layer onthe pulpal surface of the dentin and only theircytoplasmic processes are included in the tubules inthe mineralised matrix

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Each cell gives rise to one process which traverses thepredentin & calcified dentin within one tubule andterminates in a branching network to the DEJ or CDJ

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DENTINAL TUBULES

The course of the dentinal tubulesfollow a gentle curve in the crownwhere it resembles an S shape

Starts at right angles at the pulpalsurface, the first convexity of thisdoubly curved course is directedtowards the apex of the tooth

These tubules end perpendicular tothe DEJ & CDJ

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It is almost straight near the root tip and along theincisal edges and cusps

Dentin thickness ranges from 3-10mm or more

Ratio btwn outer and inner surfaces of dentine is about5:1

No. of tubules per square millimeter varies from 15000at the DEJ to 65000 at the pulp – density anddiameter increases with depth

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There are more tubules per unit area in the crownthan in the root

These dentinal tubules havelateral branches throughout dentin,which are termed canaliculi ormicrotubules

A few odontoblastic processesextend through the DEJ intothe enamel several millimetres.These are calledEnamel Spindles 28

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PERITUBULAR DENTIN

The dentin that immediately surroundsthe dentinal tubules is termedperitubular dentin

Highly mineralised than intertubular dentin

Twice as thick in outer dentin(approx. 0.75µm) thaninner dentin(approx. 0.4µm)

Calcified tubule wall has an inner organic liningtermed the Lamina Limitans which is high inglucosaminoglycans (GAG) 31


INTERTUBULAR DENTIN

Located btwn the dentinal tubules or morespecifically btwn the zones ofperitubular dentin

One half of its volume isorganic matrix, specifically collagen fibres

The fibrils range from 0.5-0.2µm in diameter andexhibit crossbanding at 64µm intervals

HA crystals are formed along the fibres withtheir long axis oriented parallel to the collagenfibres

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Well mineralised

Provide tensile strength to dentin

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PREDENTIN

Located adjacent to the pulp tissues

2-6µm, depending on the activity of odontoblasts

First formed dentin and is not mineralised

The collagen fibres undergo mineralization at thepredentin – dentin front, the predentin thenbecomes dentin and a new layer of predentinforms circumpulpally

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ODONTOBLASTIC PROCESSES

Cytoplasmic extensions of the odontoblasts

The odontoblasts reside in the peripheral pulp atthe pulp-predentin border and their processesextend into the dentinal tubules

The processes are largest in diameter near thepulp and taper further into dentin

The odontoblast cell bodies are approximately7µm in diameter & 40µm in length

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PRIMARY DENTIN

Dentin that is formed prior toeruption of a tooth.

Classified as Orthodentin, thetubular form of dentin lackingof cells found in teeth of alldentate mammals

Secreted at a relatively higherrate

Constitutes major part of thedentin in the tooth 40


PRIMARY DENTIN

Mantle dentin is the firstformed dentin in the crownunderlying the DEJ

Regular in structure

Dentinal tubules form S-shapeas a result of directionalmovement of odontoblasts

It is the outer or mostperipheral part of the primarydentin and is about 150µm thick 41


Circumpupal dentin forms the remainingprimary dentin or the bulk of the tooth

The fibrils are much smaller in diameter and aremore closely packed together

Slightly more mineral content than in mantledentin

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SECONDARY DENTIN

Formed after root completion

Narrow band of dentinbordering the pulp

Contains fewer tubules thanprimary dentin

There is usually a bend in thetubules where primary andsecondary dentin interface 43


SECONDARY DENTIN

Since it is formed aftereruption, the odontoblastsslightly change direction whichcontributes to bending ofdentinal tubules

There is usually a bend in thetubules where primary andsecondary dentin interface

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TERTIARY DENTIN

By pathologic process or operative procedures,the odontoblastic processes areexposed or cut, the odontoblastsdie or survive, depending on theextend of injury

If they survive, dentin that isproduced are called reactionary or regenerateddentin

Killed odontoblasts are replaced by the migrationof undifferentiated cells arising in the deeperlayers of the pulp to the dentin interface

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This newly differentiated odontoblasts then begindeposition of reparative dentin to seal off the zone ofinjury as a healing process initiated by the pulp,

Resulting in resolution of the inflammatory processand removal of dead cells

This type dentin produced by a new generation ofodontoblast-like cells in response to appropriatestimulus after the death of original odontoblasts iscalled Reparative dentin

This reparative dentin has fewer and more twistedtubules than normal dentin 47


Histological difference between reactionary andreparative dentin is that reactionary dentin isdeficient in acid proteins so it doesn’t stain.

Reactionary dentin appears as either osteodentintype or orthodentin type

Reparative dentin has structure-less mineralisationas in bone.

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MANTLE DENTIN

First layer of primary dentin to be deposited

Oldest dentin and produced adjacent to the enamelin the crown

Can be recognized by he characteristic thick, fanshaped collagen fibres deposited immediatelysubjacent to the basal lamina in histologic sections

Fibres run roughly perpendicular to the DEJ

150µm thick

Slightly less mineralised than underlying dentin50


When viewed under polarised light, the mantledentin (RED Band) can be differentiated from theCircumpulpal dentin (Purple with black dentinaltubules)

This is due to difference in collagen fibres inmantle dentin

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CIRCUMPULPAL DENTIN

Formed after the layer of mantle dentin has beendeposited

Constitutes major part of primary and secondarydentin

Hydroxy appatite crystals are deposited on thesurface and within the fibrils and continue to growas mineralization proceeds, resulting in anincreased mineral content of dentin

Circumpulpal dentin is mineralised throughcalcospherites in the mineralisation front betweenpredentin and mineralizing dentin

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As the calcospherites enlarge, they fuse with theadjacent calcospherites until the dentin matirx iscompletely mineralised

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INCREMENTAL LINES

The incremental lines ofVon Ebner or imbricationslines appear as fine lines orstriations in dentin

Run at right angles to the dentinal tubules.

These lines reflect the daily rhythmic, recurrentdeposition of dentin matrix as well as hesitation inthe daily formative process 54


The course of the lines indicates the growthpattern of the dentin

Some of these incremental linesare accentuated because ofdisturbances in the matrix andremineralization process.Such lines are known asContour lines of Owen

These lines represent hypocalcifiedbands

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In the deciduous teeth and in the firstpermanent molars, the prenatal andpostnatal dentin is separated by anaccentuated contour line, this istermed the Neonatal line.

This line reflects the abruptchange in environment that occurs atbirth

The dentin matrix formed prior to birth isusually of better quality than that formed afterbirth

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57Incremental lines of Von Ebner

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INTERGLOBULAR DENTIN

Sometimes mineralization of dentin begins in smallglobular areas that fail to fuse into a homogenousmass.

This results in zones of hypomineralisation btwnthe globules. These zones are called interglobulardentin.

Forms in crowns of teeth in the circumpulpal dentinjust below the mantle dentin

Seen in dental anomlies (hypophosphatasia) 60


The dentinal tubules pass uninterruptedly, thusdemonstrating a defect of mineralization and not ofmatrix formation

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GRANULAR LAYER

There is a zone adjacentto the cementum thatappears granular knownas Tome’s granular layer

It slightly increases in amount from the CEJ tothe root apex

Caused by coalescing and looping of the terminalportions of the dentinal tubules

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PHYSICAL & CHEMICAL PROPERTIES

Physical

Light yellowish in color becomes darker with age

Viscoelastic (86GPa) and subject to slight deformationunlike enamel (11-20GPa) which is hard and brittle

Harder(68kg/mm2) than bone but considerably softerthan enamel(343kg/mm2)

Lower content of mineral salts in dentin renders it moreradiolucent than enamel 64


Provides resiliency to the crown which is necessaryto withstand the forces of mastication

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Chemical

20% organic matter

10% water

70% inorganic material

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Organic substances:

Type I collagenous fibrils Type V collagenous fibrils (minor) Non collagenous proteins:

•Dentin phosphoprotien (DPP)•Dentin matrix protein 1 (DMP1)•Dentin sialoprotein (DSP)•Bone sialoprotein (BSP)•Osteopontin, Osteocalcin

Proteoglycans Phospholipids Growth factors:

•Bone morphogenetic proteins (BMP)•Insulin like growth factors (IGFs)•Transforming growth factors β (TGF- β) 67


Inorganic substances:

•Calcium hydroxy appatite crystals

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Type I collagen is the principal type of collagenfound in dentine

Inorganic crystals are plate shaped and muchsmaller than hydroxyl apatite crystals in enamel

Dentin also contains small amounts of phosphates,carbonates and sulphates.

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INNERVATION OF DENTIN

Nerve fibres were shown to accompany 30-70% ofthe odontoblastic process and these are referredto as intratubular nerves

These nerves and their terminals are found inclose association with the odontoblasts processwithin the tubule

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Theories of pain transmission through dentin

3 basic theories of pain conduction through dentin

Direct neural stimulation Transduction theory Modulation theory “Gate” control / Vibration theory Hydrodynamic theory

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DIRECT NEURAL STIMULATION

According to which nerves in the dentin getstimulated.

Drawbacks: The nerves in dentinal tubules are not commonly

seen and even if they are present, they do not extendbeyond the inner dentin

Topical application of local anaesthetic agents do notabolish sensitivity

Hence this theory is not accepted72


TRANSDUCTION THEORY

According to which the odontoblasts process is theprimary structure excited by the stimulus and that theimpulse is transmitted to the nerve endings in theinner dentin.

Drawbacks:

Since there are no neurotransmitter vesicles inthe odontoblast process to facilitate the synapse orsynaptic specialization

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MODULATION THEORY

According to which the nerve impulses in the pulp aremodulated through the liberation of polypeptides fromthe odontoblasts, when injured.

These substances may selectively alter thepermeability of the odontoblastic cell membranethrough hyperpolarisation, so that pulp neurons aremore prone to discharge upon receipt of subsequentstimuli

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“GATE” CONTROL / VIBRATION THEORY

This theory states that pain is a function of thebalance between the information travelling into thespinal chord through large nerve fibre and informationtravelling through small nerve fibres.

Large nerve fibres carry Non-nociceptiveinformation and small nerve fibres carry Nociceptiveinformation

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According to this theory, A-β fibres whichtransmit information from vibration receptorsstimulate inhibitory neurons in the spinal chord,which inturn act to reduce the amount of pain signaltransmitted from A-δ and C fibres across the midlineof the spinal chord and from there to the brain

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HYDRODYNAMIC THEORY

Most accepted theory

Various stimuli such as heat, cold, airblastdessication or mechanical or osmotic pressure affectfluid movement in the dentinal tubules.

This fluid movement either inward or outward,stimulates the pain mechanism in the tubules bymechanical disturbance of the nerves closelyassociated with the odontoblast and its process

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Thus these endings may act as mechanoreceptosas they are affected by mechanical displacementof tubular fluid

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AGE AND FUNCTIONAL CHANGES IN DENTIN

Vitality of dentin

Odontoblasts and its processes are an integral part ofdentin

And so vitality is understood to be the capacity of thetissue to react to physiologic and pathologic stimuli,dentin must be considered a vital tissue

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Dentinogenesis is a process that continues throughout life

Although after the teeth have erupted and havebeen functioning for a short time, dentinogenesisslows and further dentin formation is at a slowerrate. This is secondary dentin

Pathologic changes in dentin such as dental caries,abrasion, attrition or the cutting of dentin inoperative procedures cause changes in dentin. Theyare the dead tracts, sclerosis and the addition ofreparative dentin.

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DEAD TRACTS

The odontoblastic processesdisintegrate and the emptytubules are filled with air

Appear black in transmitted light and white inreflected light

Degeneration is often observed in areas of narrowpulp horns because of crowding of odontoblasts

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These degenerated empty areas demonstratedecreased sensitivity

Seen to a greater extend in older teeth

Dead tracts are probably the initial step in theformation of sclerotic dentin

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SCLEROTIC/TRANSPARENT DENTIN

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Caries, attrition, abrasion, erosion orcavity preparation causes collagen fibresand apatite crystals to begin appearingin the dentinal tubules

This blocking of tubules may be considered as adefensive reaction of dentin

These apatite crystals are initially only sporadicin a dentinal tubule but gradually fill it with afine meshwork of crystals


As this continues, the tubule lumen is obliterated with mineral which appears very much like the peritubular dentin

The refractive indices of dentin in such areasbecome transparent

Transparent in transmitted and dark in reflected light

There is decreased permeability of dentin

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DENTINAL FLUID

Free fluid occupies 1% of superficial dentin and 22%of total volume of deep dentin

Ultrafiltrate of blood from pulp capillaries

Contains plasma proteins

Serve as a sink from which injurious agents candiffuse into the pulp producing inflammatoryresponse

Also serve as a vehicle for egress of bacteria from anecrotic pulp into periradicular tissue. 86


CLINICAL CONSIDERATIONS

Restorative procedures

Cavity preparation – minor routine procedure – Crisis from the perspective of the pulp

Fluid shifts

Simple restorative procedure – profound effects on the pulp

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Sensitivity of dentin

On root areas exposed due to recededgums or periodontal disease.

Root of a tooth becomes exposed - it does nothave a layer of enamel but cementum

Overzealous brushing or using a very abrasivetoothpaste can also cause abrasion of the tooth’senamel surface and expose dentin.

Very acidic diet –– can cause tooth erosion anddissolve the tooth surface, exposing the dentin. 88


Permeability of dentin

Tubular structure of dentin provides passage ofsolutes and solvents across dentin

Lowest at the DEJ and highest at the pulp –diameter increases with depth

Divided into 2 categoriesTransdentinal movement – fluid shifts in

hydrodynamic stimuliIntradentinal movement – as occurs

infilteration of hydrophilic resins intodemineralised dentin surfaces

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Smear layer & Smear plugs

Smear Layer - term most often used to describe the grinding debris left on dentin by cavity preparation

Cutting debris when forced into dentinal tubules, it forms plugs known as smear plugs

Smear layer : 1-3 µm Smear plug : 40 µm

Significance - Lowers the permeability of dentin surface 91

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Remaining dentin thickness (RDT)

The major factor in odontoblast response and indentin formation

Odontoblast injury increases as the cavity RDTdecreases.

Below 0.25 mm the number of odontoblastsdecreases by 23%, and minimal reactionary dentinrepair is observed.

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Affected & Infected dentin

Infected dentin is that part of dentin which iscontaminated and contains the microorganism withtheir toxins, and demineraliaed dentin.

Affected dentin is not occupied by microorganism itjust contains the toxins produced by microorganismsof the infected dentin, and also there isdemineralization.

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The collagen fibres are denatured in Infecteddentin while in Affected dentin, the collagen fibresdemonstrates cross-banding and is physiologicallyremineralizable

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CONCLUSION

Developmentally pulpal cells produce dentin,nerves and blood vessels.

Although dentin and pulp have differentstructures, once they are formed, they react tostimuli as a functional unit.

Exposure of dentin through attrition, caries ortrauma produces profound pulpal reactions thattend to reduce permeability and stimulateformation of additional dentin.

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REFERENCES

Orbans oral histology and embryology

Tencates Oral histology

Dental Pulp – Seltzer and Bender

Pathways of the pulp - Cohen

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Education

Dentin