PERIODONTIUM (10) [EDocFind.com]

8/7/2019 PERIODONTIUM (10) [EDocFind.com]

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PERIODONTIUMPERIODONTIUM

Oral HistologyOral HistologyDent 206Dent 206


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PeriodontiumPeriodontium

Four tissue supporting the tooth in the jawFour tissue supporting the tooth in the jaw

CementumCementum

Periodontal ligamentPeriodontal ligament Alveolar boneAlveolar bone

GingivaeGingivae


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CementumCementum

Thin layer of calcified tissue covering the root inThin layer of calcified tissue covering the root inthethe humanhuman teethteeth

Present in the crowns of some mammalsPresent in the crowns of some mammals Adaptation to herbivorous dietAdaptation to herbivorous diet

One of four tissues supporting the toothOne of four tissues supporting the tooth(periodontium)(periodontium)

The least known ofThe least known of Periodontium tissuesPeriodontium tissues

All mineralized tissuesAll mineralized tissues


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CementumCementum

Varies in thicknessVaries in thickness

Thick @ apex (50Thick @ apex (50--200 m) & inter200 m) & inter--radicular regionsradicular regions

Thin cervically (10Thin cervically (10--15 m)15 m)

Contiguous with PDLContiguous with PDL

Firmly adherent with root dentineFirmly adherent with root dentine

Highly responsive mineralized tissueHighly responsive mineralized tissue Maintenance of root integrityMaintenance of root integrity

Maintenance of functional position ofMaintenance of functional position oftoothtooth

Tooth repair & regenerationTooth repair & regeneration


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CementumCementum

SlowlySlowly--formed throughout lifeformed throughout life

Allowing continual reattachment of PDL fibersAllowing continual reattachment of PDL fibers

Cementum can be regarded as a mineralizedCementum can be regarded as a mineralizedcomponent of PDLcomponent of PDL

PrecementumPrecementum -- a thin mineralized layer on thea thin mineralized layer on thesurface of the cellular cementumsurface of the cellular cementum

Similar to bone, howeverSimilar to bone, however -- Avascular & not innervatedAvascular & not innervated

Less rapidly resorbedLess rapidly resorbed orthodonticsorthodontics


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CementCement--enamelenamel

junctionjunction

Pattern IPattern I

Cementum overlaps enamel for a short distanceCementum overlaps enamel for a short distance Most predominantMost predominant 60% of sections60% of sections

Pattern IIPattern II Enamel meet cementum at butt jointEnamel meet cementum at butt joint

Occurs in 30% of sectionsOccurs in 30% of sections Pattern IIIPattern III

Enamel fails to meet cementumEnamel fails to meet cementum

Dentine between them is exposedDentine between them is exposed

10% of sections10% of sections


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Physical propertiesPhysical properties

Pale yellowPale yellow

Softer than dentineSofter than dentine

PermeabilityPermeabilityVaries with age and type of cementumVaries with age and type of cementum Decreases with ageDecreases with age

Cellular is more permeableCellular is more permeable

More permeable than dentineMore permeable than dentine

Readily removed by abrasion after gingivalReadily removed by abrasion after gingivalrecessionrecession


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Chemical propertiesChemical properties

InorganicInorganic OrganicOrganic WaterWater

By weightBy weight 65%65% 23%23% 12%12%

By volumeBy volume 45%45% 33%33% 22%22%

Hydroxyapatite crystals similar to those in boneHydroxyapatite crystals similar to those in bone

More concentration of trace elements (F) at surfaceMore concentration of trace elements (F) at surface

F levels higher in acellularF levels higher in acellular

Collagenous organic matrix, primarily type ICollagenous organic matrix, primarily type I

Molecules involved in PDL fiber reattachment &/orMolecules involved in PDL fiber reattachment &/ormineralizationmineralization Bone sialoprotein, osteopontin & cementumBone sialoprotein, osteopontin & cementum--specific elementsspecific elements


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Classification of cementumClassification of cementum

Presence or absence of cellsPresence or absence of cells

Cellular cementumCellular cementum

Acellular cementumAcellular cementum Nature & origin of organic matrixNature & origin of organic matrix

Extrinsic fiber cementumExtrinsic fiber cementum

Intrinsic fiber cementumIntrinsic fiber cementum

Mixed fiber cementumMixed fiber cementum

CombinationsCombinations


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Acellular cementumAcellular cementum

Most common patternMost common pattern-- adjacent to dentineadjacent to dentine

StructurelessStructureless

Afibrillar cementumAfibrillar cementum Exists betweenExists between


Hyaline layer (of HopewellHyaline layer (of Hopewell--Smith)Smith)

Mineralized GSMineralized GS Covers cervical enamelCovers cervical enamel

Results following loss ofREEResults following loss ofREE


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Root dentine

Fibres of

PeriodontalLigament

CementumEpithelial

Rests


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Most common patternMost common pattern Apical areaApical area

InterInter--radicular areasradicular areas

Overlying acellular dentineOverlying acellular dentine

CementocytesCementocytes InactiveInactive

In lacunaeIn lacunae appear dark in GSappear dark in GS Processes present in canaliculiProcesses present in canaliculi

Processes connected via gap junctionsProcesses connected via gap junctions


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Cementocytes vs.Cementocytes vs.

osteocytesosteocytes CementocytesCementocytes

More widely dispersedMore widely dispersed

R

andomly arrangedR

andomly arranged Canaliculi oriented towardsCanaliculi oriented towards

PDLPDL nutritionnutrition

OsteocytesOsteocytes

OsteonOsteon Haversian systemHaversian system

Organized cellsOrganized cells

Circumferential lamellaeCircumferential lamellae


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Relationship between acellular &Relationship between acellular &

cellular cementumcellular cementum More common patternMore common pattern

AcellularAcellular cervicallycervically

Acellular closer to dentineAcellular closer to dentine CellularCellular apicallyapically

Cellular covers acellularCellular covers acellular

Less common patternsLess common patterns

AlternatingAlternating

Acellular overlies cellularAcellular overlies cellular


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Extrinsic & intrinsic fiber cementumExtrinsic & intrinsic fiber cementum

Extrinsic fiber cementumExtrinsic fiber cementum

Fibers derived from insertingSharpys fibers of PDLFibers derived from insertingSharpys fibers of PDL

Intrinsic fiber cementumIntrinsic fiber cementumRun parallel to root surface at right angles toRun parallel to root surface at right angles to

extrinsic fibersextrinsic fibers

Fibers derived from cementoblastsFibers derived from cementoblasts


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Acellular extrinsic fiber cementumAcellular extrinsic fiber cementum

AEFCAEFC

Over cervical halfOver cervical half 2/3s of the root2/3s of the root

Bulk of cementum in premolarsBulk of cementum in premolars First formed cementumFirst formed cementum -- acellularacellular

Thickness of 15 mThickness of 15 m

All collagen are from Sharpys fibersAll collagen are from Sharpys fibers

Though GS from cementoblastsThough GS from cementoblasts

Fibers wellFibers well--mineralizedmineralized


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Cellular intrinsic fiber cementumCellular intrinsic fiber cementum

CIFCCIFC

Fibers deposited by cementoblastsFibers deposited by cementoblasts

F

ibers run parallel to root surfaceF

ibers run parallel to root surface No role of tooth attachmentNo role of tooth attachment

In apical 1/3 & interIn apical 1/3 & inter--radicular areasradicular areas

May beMay beTemporaryTemporary extrinsic fibers gain reattachmentextrinsic fibers gain reattachment

PermanentPermanent without attaching fiberswithout attaching fibers


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Acellular intrinsic fiber cemetumAcellular intrinsic fiber cemetum

If cementum forms slowly in CIFCIf cementum forms slowly in CIFC


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Cellular mixed stratified cementumCellular mixed stratified cementum

Alternating AEFC with CIFCAlternating AEFC with CIFC

Root apexRoot apex

Furcation areasFurcation areas


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MixedMixed--fiber cementumfiber cementum

Collagen fibers derived fromCollagen fibers derived from Extrinsic fibersExtrinsic fibers

Intrinsic fibersIntrinsic fibers

Intrinsic fibers run between the extrinsic fibersIntrinsic fibers run between the extrinsic fibers

Two typesTwo types rate of formationrate of formation Acellular mixedAcellular mixed--fiber cementumfiber cementum

Well mineralized fibersWell mineralized fibers Cellular mixedCellular mixed--fiber cementumfiber cementum

Less well mineralized fibersLess well mineralized fibers


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Cemental incremental linesCemental incremental lines

Irregular rhythm of depositionIrregular rhythm of deposition

Not related to activity & quiescenceNot related to activity & quiescence

R

elated toR

elated to Difference in the degree of mineralizationDifference in the degree of mineralization Composition of organic matrixComposition of organic matrix

Imprecise periodicityImprecise periodicity

AcellularAcellular closer, thinner & regular linescloser, thinner & regular lines

CellularCellular -- farther apart, thicker & irregular linesfarther apart, thicker & irregular lines


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Incremental linesIncremental lines

Cementum is formed rhythmically and can beCementum is formed rhythmically and can be

seen as being composed of layersseen as being composed of layers


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Resorption & repair of cementumResorption & repair of cementum

Less susceptibility to resorption than boneLess susceptibility to resorption than bone

Localized resorption areas occurLocalized resorption areas occur

Could be caused by microtraumaCould be caused by microtrauma May continue to root dentineMay continue to root dentine

By multinucleated odontoclastsBy multinucleated odontoclasts

Resorption filled by mineralized tissueResorption filled by mineralized tissue(resembles cellular cementum)(resembles cellular cementum)

Reversal lineReversal line


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Reparative cementum vs. cementumReparative cementum vs. cementum

Wider uncalcified zoneWider uncalcified zone

Less mineralizedLess mineralized

Smaller crystalsSmaller crystals Calcific globules are presentCalcific globules are present

Differences are related to different speed of formationDifferences are related to different speed of formation


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Clinical considerationsClinical considerations

Cemental callusCemental callus

Root fractureRoot fracture

N

o remodeling to original dimensions of the rootN

o remodeling to original dimensions of the root CementiclesCementicles

Free or attached pieces in PDLFree or attached pieces in PDL

MicrotraumaMicrotrauma

Apical & middle 1/3s of rootApical & middle 1/3s of root

Root furcationRoot furcation


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Clinical considerationsClinical considerations

SupraSupra--eruption of teetheruption of teeth

Tooth wearTooth wear

Local hypercementosisLocal hypercementosis

Reaction to PA inflammationReaction to PA inflammation

Difficulty in extractionDifficulty in extraction

Pagets diseasePagets disease multiple teeth withmultiple teeth withhypercementosishypercementosis

Cementum narrowing root canal andCementum narrowing root canal andshifting the junction between dentalshifting the junction between dentalpulp & PDL cervicallypulp & PDL cervically

Pulp removal in RCT up to that pointPulp removal in RCT up to that point


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Periodontal ligament PDLPeriodontal ligament PDL

Dense fibrous connective tissueDense fibrous connective tissue

Occupies the area between the root of the toothOccupies the area between the root of the tooth

and the walls of the alveolar socketand the walls of the alveolar socket Derived from the dental follicleDerived from the dental follicle

Continuous withContinuous with

the connective tissue of the gingiva above thethe connective tissue of the gingiva above thealveolar crestalveolar crest

The dental pulp at the apical foramenThe dental pulp at the apical foramen


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Periodontal ligament spacePeriodontal ligament space

Variable in width, average 0.2Variable in width, average 0.2mmmm

looks hourglass in shapelooks hourglass in shape

Reduced in unerupted & nonReduced in unerupted & non--functional teethfunctional teeth

Increased in teeth subjectedIncreased in teeth subjected

to heavy occlusal stressto heavy occlusal stress Narrows slightly with ageNarrows slightly with age

Narrower in permanent teethNarrower in permanent teeth


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Functions of PDLFunctions of PDL

AttachmentAttachment

Has a role in tooth eruption andHas a role in tooth eruption and

supportsupport

Its cells repair the alveolar bone &Its cells repair the alveolar bone &

cementumcementum Neurological control of masticationNeurological control of mastication

through its mechanoreceptorsthrough its mechanoreceptors


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Components of PDLComponents of PDL

FibersFibers

Ground substanceGround substance

CellsCells


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Fibers of PDLFibers of PDL

CollagenCollagen

Type I (70% of fibers)Type I (70% of fibers)

Type III (20% of fibers)Type III (20% of fibers)

Found in the periphery ofSharpys fibers attachment into alveolar boneFound in the periphery ofSharpys fibers attachment into alveolar bone

Small amounts of type V, VI as well as basement membrane collagen IVSmall amounts of type V, VI as well as basement membrane collagen IV& VII associated with the epithelial rests& VII associated with the epithelial rests

Highest turnover of collagen is in PDLHighest turnover of collagen is in PDL

Higher near apexHigher near apex

Even across the width of PDLEven across the width of PDL

Rate could be related to the amount of occlusal stressRate could be related to the amount of occlusal stress Oxytalan (in humans) or elastinOxytalan (in humans) or elastin

Attached into cementumAttached into cementum

May have a role in tooth supportMay have a role in tooth support


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Principal fibers of PDLPrincipal fibers of PDL

Fibers exist as bundles (principalFibers exist as bundles (principal

fibers) running in differentfibers) running in differentorientations in different regionsorientations in different regions Dentoalveolar crest fibersDentoalveolar crest fibers

Horizontal fibersHorizontal fibers

Oblique fibersOblique fibers Apical fibersApical fibers

Interradicular fibersInterradicular fibers From crest of interradicular septum toFrom crest of interradicular septum to

furcationfurcation


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Principal fibers of PDLPrincipal fibers of PDL


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Sharpys fibersSharpys fibers

Principal fibersPrincipal fibers

embedded intoembedded intocementum andcementum and

bonebone

More numerous butMore numerous but

smaller at cementalsmaller at cemental

endend

Mineralized andMineralized andunmineralized partsunmineralized parts


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Ground substance of PDLGround substance of PDL

60% of PDL by volume60% of PDL by volume

Main componentsMain components Hyaluronate GAGsHyaluronate GAGs

ProteoglycansProteoglycans

GlycoproteinsGlycoproteins

Functions of GSFunctions of GS

Ion and water binding & exchangeIon and water binding & exchange Control of collagen fibrillogenesis & fiberControl of collagen fibrillogenesis & fiber

orientationorientation

Tooth support & eruptionTooth support & eruption -- high tissue fluidhigh tissue fluid

pressurepressure


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Cells of PDLCells of PDL FibroblastsFibroblasts

Fusiform cells with manyFusiform cells with manyprocessesprocesses

FunctionsFunctions secretion andsecretion andturnover of fibersturnover of fibers Regeneration of tooth supportRegeneration of tooth support

apparatusapparatus Adaptive responses toAdaptive responses to

mechanical loadingmechanical loading CementoblastsCementoblasts

CementCement--forming cells liningforming cells liningcemental surfacecemental surface

Cuboidal cellsCuboidal cells

OsteoblastsOsteoblasts BoneBone--forming cells liningforming cells lining

tooth sockettooth socketResemble cementoblastsResemble cementoblasts


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Cells of PDLCells of PDL

Cementoclasts & osteoclastsCementoclasts & osteoclasts

Resorbing cellsResorbing cells

Howships lacunaeHowships lacunae

Epithelial rests cellsEpithelial rests cells Cuboidal cells that stain deeplyCuboidal cells that stain deeply

Close to cemental surfaceClose to cemental surface

Defence cellsDefence cells

MacrophagesMacrophages

Mast cellsMast cells

EosinophilsEosinophils


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Blood vessels of PDLBlood vessels of PDL

Separate from those entering pulpSeparate from those entering pulp

Some from alveolar bone through foraminaSome from alveolar bone through foramina

Some from pulp through accessory canalsSome from pulp through accessory canals

Major vessels lie between principal fiber bundle close toMajor vessels lie between principal fiber bundle close toalveolar bonealveolar bone

Capillary plexus around the toothCapillary plexus around the tooth

Crevicular plexus of capillary loopsCrevicular plexus of capillary loops Veins do not follow arteries but drain into intraalveolarVeins do not follow arteries but drain into intraalveolar

venous networksvenous networks


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Innervation of PDLInnervation of PDL

SensorySensory

NociceptionNociception

MechanoreceptionMechanoreception

Sensitivity to occlusal loadsSensitivity to occlusal loads

Guidance to intercuspationGuidance to intercuspation

AutonomicAutonomic

Associated with blood vesselsAssociated with blood vessels


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Alveolar processAlveolar process

The alveolar process develops during theThe alveolar process develops during the

eruption of teetheruption of teeth

Grows at a rapid rate at the free borderGrows at a rapid rate at the free border Proliferates at the alveolar crestProliferates at the alveolar crest

No distinct boundary exists between the body ofNo distinct boundary exists between the body of

the maxilla or mandible and the alveolar processthe maxilla or mandible and the alveolar process If teeth are lost the alveolar bone disappearsIf teeth are lost the alveolar bone disappears


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Development of bony cryptDevelopment of bony crypt

Deciduous tooth &Deciduous tooth &permanent successorpermanent successorinitially share cryptinitially share crypt

Bone subsequently formsBone subsequently formsto encase permanentto encase permanenttoothtooth

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PERIODONTIUM (10) [EDocFind.com]