Development of Root um

DEVELOPMENT OF ROOT DEVELOPMENT OF ROOT & PERIODONTIUM& PERIODONTIUM

Oral HistologyOral HistologyDent 206Dent 206

Root developmentRoot development Some time after enamel completionSome time after enamel completion Interaction betweenInteraction between

Dental follicleDental follicleEpithelial root sheath (of Hertwig)Epithelial root sheath (of Hertwig)

A structure derived from cervical loop region of enamel A structure derived from cervical loop region of enamel organorgan

Dental papillaDental papilla Onset coincides with axial phase of tooth Onset coincides with axial phase of tooth

eruptioneruption

Epithelial root sheath (ERS)Epithelial root sheath (ERS)

Forms at the late bell stageForms at the late bell stage Amelogenesis and dentinogenesis Amelogenesis and dentinogenesis

are well-advancedare well-advanced Double-layeredDouble-layered

Internal enamel epitheliumInternal enamel epithelium External enamel epitheliumExternal enamel epithelium

No SR or SINo SR or SI Apical proliferationApical proliferation Mapping out the shape of the Mapping out the shape of the

crowncrown Never a continuous sheath – Never a continuous sheath –

disintegrationdisintegration

Enamel PearlEnamel Pearl Localized areas of enamel on root surfaceLocalized areas of enamel on root surface Usually in inter-radicular regions of molarsUsually in inter-radicular regions of molars Retention of SR & SI inside the double-Retention of SR & SI inside the double-

layered ERSlayered ERS

ERS in mutli-rooted teethERS in mutli-rooted teeth Primary apical foramen subdivide Primary apical foramen subdivide

into a number of secondary apical into a number of secondary apical foraminaforamina

Ingrowth of epithelial shelves from Ingrowth of epithelial shelves from the margins of ERSthe margins of ERS

Fuse near the center of the rootFuse near the center of the root Number & location of shelvesNumber & location of shelves

Corresponds to the number of rootsCorresponds to the number of roots May be under inductive role of dental May be under inductive role of dental

papillapapilla Ingrowth is believed to occur along Ingrowth is believed to occur along

paths of low vascularitypaths of low vascularity

Primary apical foramenPrimary apical foramen While the root is being formedWhile the root is being formed

Apex is wide “open”, surrounded by:Apex is wide “open”, surrounded by: Thin regular knife edge of dentineThin regular knife edge of dentine

A permanent toothA permanent tooth Erupts with about 2/3s of formed rootErupts with about 2/3s of formed root Needs 3 or more years before root Needs 3 or more years before root

completioncompletion By root completion, the wide apical By root completion, the wide apical

foramen becomes very narrowforamen becomes very narrow Only wide to transmit the Only wide to transmit the

neurovascular bundleneurovascular bundle

Growth of ERSGrowth of ERS Occurs apicallyOccurs apically Encloses dental papillaEncloses dental papilla

Except at primary apical Except at primary apical foramenforamen

Margin of ERS is angled Margin of ERS is angled internally to forminternally to form Root diaphragmRoot diaphragm

Dental follicleDental follicle Lies external to ERSLies external to ERS Forms cementum, PDL & Forms cementum, PDL &

alveolar bonealveolar bone

Root diaphragmRoot diaphragm The angled edge of ERSThe angled edge of ERS A circular bandA circular band Sandwiched between the undifferentiated Sandwiched between the undifferentiated

mesenchyme ofmesenchyme ofDental papillaDental papillaDental follicleDental follicle

Commencement of root dentinogenesisCommencement of root dentinogenesis

Cells of internal layer of Cells of internal layer of ERSERSInduce peripheral cells of Induce peripheral cells of

dental papilladental papillaDifferentiate into Differentiate into

odontoblastsodontoblastsRoot dentine is depositedRoot dentine is deposited

Commencement of cementogenesisCommencement of cementogenesis Root dentine is depositedRoot dentine is deposited ERS cells lose continuityERS cells lose continuity

Form epithelial rests (of Form epithelial rests (of Malassez) in PDLMalassez) in PDL

Root dentine is exposed to Root dentine is exposed to the undifferentiated cells of the undifferentiated cells of the dental folliclethe dental follicle

Differentiate into Differentiate into cementoblastscementoblasts

CementogenesisCementogenesis

Dental follicle near the diaphragmDental follicle near the diaphragm 3 layers3 layers

Inner investing layerInner investing layer Ectomesenchymal – neural crestEctomesenchymal – neural crest Cells differentiate into cementoblastsCells differentiate into cementoblasts Cuboidal cells on root dentine surfaceCuboidal cells on root dentine surface

Intermediate layerIntermediate layer Mesodermal originMesodermal origin Cells differentiate into fibroblastsCells differentiate into fibroblasts Forming PDLForming PDL

Outer layerOuter layer Mesodermal originMesodermal origin Cells differentiate into osteoblastsCells differentiate into osteoblasts Forming alveolar boneForming alveolar bone

DF after commencement of DF after commencement of cementogensiscementogensis

Follicular cells are Follicular cells are obliquely oriented along obliquely oriented along the root surfacethe root surface

Become the fibroblasts Become the fibroblasts of PDLof PDL

Fibroblasts secrete Fibroblasts secrete collagen which become collagen which become embedded in developing embedded in developing cementum and alveolar cementum and alveolar bone (Sharpy’s fibers)bone (Sharpy’s fibers)

Root completionRoot completion

When the final root length is achieved, When the final root length is achieved, the proliferation of epithelium in the the proliferation of epithelium in the diaphragm lags behind that of the pulp or diaphragm lags behind that of the pulp or connective tissueconnective tissue

The wide apical foramen is reduced first - The wide apical foramen is reduced first - to the width of the diaphragmatic opening to the width of the diaphragmatic opening

itself itself further narrowed by apposition of dentine and further narrowed by apposition of dentine and

cementum at the apex of the rootcementum at the apex of the root

Accessory root canalsAccessory root canals If continuity of root sheath is broken or not If continuity of root sheath is broken or not

established prior to dentine formation a defect in the established prior to dentine formation a defect in the dentinal wall of the pulp occursdentinal wall of the pulp occurs

Root elongation & tooth eruptionRoot elongation & tooth eruption

Root growth theory of eruptionRoot growth theory of eruption Changes in apical connective Changes in apical connective

tissuetissue Old view - cushion Old view - cushion

hammock ligamenthammock ligamentFibrous with fluid filled Fibrous with fluid filled

intersticesintersticesAttachment on either sides to Attachment on either sides to

alveolar bonealveolar boneResistant base – prevents bone Resistant base – prevents bone

resorption – eruptive forceresorption – eruptive force

Root growth theory of eruptionRoot growth theory of eruption Current view – pulp limiting Current view – pulp limiting

membranemembrane No attachment to alveolar boneNo attachment to alveolar bone But merges with developing PDLBut merges with developing PDL Surgical removal – no effect on Surgical removal – no effect on

eruptioneruption TheoryTheory

Changes in vascular permeabilityChanges in vascular permeability Dense accumulation of tissue fluidDense accumulation of tissue fluid Fluid force bone and root apartFluid force bone and root apart Contribution to eruptionContribution to eruption

Formation of principal PDL fibersFormation of principal PDL fibers Stage 1 – before eruptionStage 1 – before eruption

PDL – loosely structured collagenous elementsPDL – loosely structured collagenous elementsPermanent molarsPermanent molars

Dentogingival & oblique fibers are organizedDentogingival & oblique fibers are organizedPremaloarsPremaloars

Only dentogingival fibers are well-developedOnly dentogingival fibers are well-developed

Formation of principal PDL fibersFormation of principal PDL fibers Stage 2 – tooth penetrationStage 2 – tooth penetration

PDL – fibers developed but not spanning PDL PDL – fibers developed but not spanning PDL spacespace

Permanent molarsPermanent molarsPDL well-differentiatedPDL well-differentiatedOblique fibersOblique fibers

PremolarsPremolarsOnly alveolar crest fibers are organizedOnly alveolar crest fibers are organized

Formation of principal PDL fibersFormation of principal PDL fibers Stage 3 – reaching occlusionStage 3 – reaching occlusion

Permanent molarsPermanent molarsFibers in cervical region are organizedFibers in cervical region are organized

PremolarsPremolarsProminent cervical fibersProminent cervical fibersUndeveloped in apical part of the rootUndeveloped in apical part of the root

Stage 4 – functionalStage 4 – functionalClassical organization of principal fibersClassical organization of principal fibers

Additional notes on formation of Additional notes on formation of principal PDL fibersprincipal PDL fibers

Collagen fibers are only organized in functionCollagen fibers are only organized in functionEruptive force caused by traction of collagen in Eruptive force caused by traction of collagen in

PDL development is debatablePDL development is debatable Change in obliquity & thickness of fibers as Change in obliquity & thickness of fibers as

the tooth reaches the functional positionthe tooth reaches the functional positionInclination decreasesInclination decreasesThickness with functionThickness with function

Additional notes on formation of Additional notes on formation of principal PDL fibersprincipal PDL fibers

During eruption – resorption of the bone in the During eruption – resorption of the bone in the base of the socket is predominantbase of the socket is predominantBone deposition is not accepted as a cause of Bone deposition is not accepted as a cause of

eruptioneruptionHowever, species differ (deposition in dogs)However, species differ (deposition in dogs)Bone activity is related to the distance the tooth Bone activity is related to the distance the tooth

has to erupthas to eruptDistance greater than root length – depositionDistance greater than root length – deposition

CementogenesisCementogenesis Primary (acellular) cementumPrimary (acellular) cementum

Cervical portion of the rootCervical portion of the root Secondary (cellular) cementumSecondary (cellular) cementum

Apical region of the rootApical region of the rootFurcation areasFurcation areas

Formation of acellular cementumFormation of acellular cementum

Starts cervically and proceeds Starts cervically and proceeds apicallyapically

Cells of ERSCells of ERS Do not enlarge as in enamel organDo not enlarge as in enamel organ Separated by a basal lamina on both Separated by a basal lamina on both

sidessides Induction of root dentinogenesisInduction of root dentinogenesis Odontoblasts retreat inwardsOdontoblasts retreat inwards Form first-formed root predentineForm first-formed root predentine

No odontoblastic process yetNo odontoblastic process yet Structureless Structureless Hyaline layer when fully mineralizedHyaline layer when fully mineralized

Formation of Formation of acellular cementumacellular cementum

ERS in contact with predentineERS in contact with predentine Disintegration of ERS cellsDisintegration of ERS cells Exposure of follicular cells to Exposure of follicular cells to

unmineralized hyaline layerunmineralized hyaline layer Differentiation into Differentiation into

cementoblastscementoblasts Cementoblasts secrete collagen Cementoblasts secrete collagen

fibrilsfibrils Deep parts of fibrils intermingle Deep parts of fibrils intermingle

with those of the hyaline layer – with those of the hyaline layer – strong unionstrong union

Peripheral parts extend into PDL Peripheral parts extend into PDL (fibrous fringe)(fibrous fringe)

Formation of acellular cementumFormation of acellular cementum Mineralization ofMineralization of

Hyaline layerHyaline layerFibrous fringeFibrous fringe

Thus, first formed acellular cementum are Thus, first formed acellular cementum are firmly attached to root dentinefirmly attached to root dentine

Fibers of PDL are still parallel to root surface Fibers of PDL are still parallel to root surface & not yet attached to fibrous fringe& not yet attached to fibrous fringe

Formation of primary (acellular) Formation of primary (acellular) cementumcementum

Slow increase in thickness of acellular Slow increase in thickness of acellular cementumcementum

Establishment of continuity between fibrous Establishment of continuity between fibrous fringe and PDL fibersfringe and PDL fibers

Continued slow mineralization of collagenContinued slow mineralization of collagen

Types of acellular cementumTypes of acellular cementum Acellular intrinsic fiber cementumAcellular intrinsic fiber cementum

Acellular cementum lining the root before its Acellular cementum lining the root before its fringe fibers are linked with those of PDLfringe fibers are linked with those of PDL

In permanent teeth, exist until tooth erupts into the In permanent teeth, exist until tooth erupts into the mouthmouth

Acellular extrinsic fiber cementumAcellular extrinsic fiber cementumAcellular cementum lining the root after its fringe Acellular cementum lining the root after its fringe

fibers are linked with those of PDLfibers are linked with those of PDLIncreases in thickness slowly & evenly throughout Increases in thickness slowly & evenly throughout

life life

Mineralization in acellular cementumMineralization in acellular cementum

Presence of crystals is adjacent dentine is believed to Presence of crystals is adjacent dentine is believed to initiate mineralization in cementuminitiate mineralization in cementum

Adjacent PDL fibroblasts may play a roleAdjacent PDL fibroblasts may play a role Very slow processVery slow process No calcospheritesNo calcospherites No layer of unmineralized “precementum”No layer of unmineralized “precementum” Incremental linesIncremental lines

High content of ground substanceHigh content of ground substance Low content of collagenLow content of collagen Closer together than in cellular cementum – slow formationCloser together than in cellular cementum – slow formation

BisphosphonateBisphosphonate Bisphosphonate inhibit cementogenesisBisphosphonate inhibit cementogenesis

Interferes with mineralization of initial root Interferes with mineralization of initial root dentinedentine

No mineralization of the hyaline layerNo mineralization of the hyaline layerNo cementogenesisNo cementogenesis

Acellular afibrillar cementumAcellular afibrillar cementum A thin layer overlying cervical margin of A thin layer overlying cervical margin of

enamelenamel Damaged reduced enamel epitheliumDamaged reduced enamel epithelium Follicle cells contact enamelFollicle cells contact enamel Differentiation into cementoblastsDifferentiation into cementoblasts Cementoblasts secrete afibrillar matrix that Cementoblasts secrete afibrillar matrix that

calcifiescalcifies

Secondary (cellular) cementumSecondary (cellular) cementum Appears at the time of eruptionAppears at the time of eruption Reflects increase in rate of cementogenesisReflects increase in rate of cementogenesis Early inductive changes are similar to those in Early inductive changes are similar to those in

acellular cementumacellular cementum Cells forming cellular cementumCells forming cellular cementum

Appear as a distinct layer of basophilic cells (RER Appear as a distinct layer of basophilic cells (RER – active protein synthesis)– active protein synthesis)

More cytoplasmic processesMore cytoplasmic processes

Cellular cementumCellular cementum

Effect of high rate of cementogenesis Effect of high rate of cementogenesis in cellular cementumin cellular cementum

High rate of formation – appearance of High rate of formation – appearance of precementumprecementum

Less mineralized than acellular cementumLess mineralized than acellular cementum Multipolar mode of mineralization – cells Multipolar mode of mineralization – cells

incorporated within matrix – cellular incorporated within matrix – cellular appearance of cementumappearance of cementum

Cementoblasts become cementocytesCementoblasts become cementocytes Generation of new cementoblasts at surfaceGeneration of new cementoblasts at surface Incremental lines more widely spacedIncremental lines more widely spaced

What Can Go WrongWhat Can Go Wrong

Cementum will not form if epithelial cells are in Cementum will not form if epithelial cells are in contact with dentinecontact with dentine

Acellular cementumAcellular cementum

•Root dentine

•Fibres of Periodontal Ligament

•Cementum•Epithelial Rests

Cellular cementumCellular cementum