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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