Development of um

8/3/2019 Development of um

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DEVELOPMENT OF PERIODONTIUM

BY

DR.SONIA MOHSIN.


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DEFINITION

tissues that support and invest the tooth arecalled periodontium

They include

Gingiva

Periodontal ligament

Alveolar bone

Cementum


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The tooth forms aspecialized fibrous joint

through theperiodontium known as

GOMPHOSIS

to understand

development ofperiodontium a recap oftooth development isessential.


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RECAP OF TOOTHDEVELOPMENT

Development starts atthe 6th week ofintrauterine life whenthe primitive mouth

develops thePRIMARY EPITHELIAL

BAND


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The primary epithelialband thickens and form2 laminas

Dental lamina

Vastibular lamina


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The tooth goes thru 4stages till the finalcrown shape isachieved

Bud stage

Cap stage

Bell stage

Crown stage.



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cap stageOral epithelium

Dental organ

Dental follicle

Dental papilla


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bell stage Stellate reticulum

Internal dental epithelium

Stratum intermedium

Dental papilla

Cervical loop

External dental epithelium


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Crown stage: The dental papilla cells

adjacent to the internaldental epitheliumdifferentiate intoODONTOBLAST.

The internal dentalepithelium cellsdifferentiate intoAMELOBLAST.



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ROOT DEVELOPMENT

bell stage

Stellate reticulum

Internal dental epithelium

Stratum intermedium

Dental papilla

Cervical loop

External dental epithelium


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ROOT DEVELOPMENT

bell stage

Cervical loop

This forms the root.


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ROOT DEVELOPMENT Hertwigz root sheath: It forms by the union of external

n internal dental epithelium andconverges to form the root. F = internal dental epithelium. E = external dental epithelium B = dental papilla D = dental follicle C = primitive apical foramen

A = hertwigz root sheath. The internal cells of the hertwigs

root sheath differentiate to formodontoblast that lays down theroot dentine.



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ROOT DEVELOPMENT


odontoblasts that wouldlay down the root dentine-DENTINOGENESIS

This is whereCEMENTOGENESISwould begin after thehertwigs root sheath

fragments.


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CEMENTOGENESIS : When the cells of hertwigs

root fragment the cells ofdental follicle come intocontact with the dentineformed by the internal dentalepithelium.

Cells of the dental folliclestart to differentiate and formcementoblast.

These cementoblasts formthe cementum on the rootdentine. dentine


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CEMENTOGENESIS

Cementogenesis is of 2 types Primary cementum formation

Secondary cementum formation.

Before understanding the process of cementum

formation its important to understand the followingstructure

Hyaline layer of hopewell smith


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HYALINE LAYER OF HOPEWELLSMITH :

it is a structurless, highlymineralized layer havingenamel like proteins andfunctioning to cementcementum to dentine.

Formation :Before fragmenting the hertwigs

root sheath gives out enamellike proteins next to the rootdentine, later this layerbecomes mineralized and formsa layer called hyaline layer ofhopewell smith.

Hence it lies between the rootdentine and the newly formedcementoblasts.

Primarycementum

Dentine

Hyaline layerof hopewellsmith


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PRIMARY CEMENTUM

CHARACTERISTICS : It forms at a slower rate as

compared to secondarycementum

It is more mineralized as

compared to secondarycementum.

It is present in the coronal 2/3rdof the root only.

It is acellular


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PRIMARY CEMENTUMFORMATION : When the cells of the hertwigs

root sheath fragment the dentalfollicle differentiates intocementoblasts by the followingways. They increase in size They increase the organelles

within them.

The cementoblasts extendprocesses into the hyaline layerof hopewell smith and deposit Collagen bundles Non-collagenous proteins

(bone sialoprotiens &osteocalcin)


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PRIMARY CEMENTUMFORMATION : The collagen deposited forms a

fibrous fringe and is at rightangles to the long axis of theroot.

This matrix then becomesmineralized and formscementum.

Cementoblasts move away andkeep depositing cementum untilthey come in contact with thefibroblasts forming theperiodontal ligaments.


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SECONDARY CEMENTUM

CHARACTERISTICS : It forms at a faster rate as

compared to secondarycementum.

It is less mineralized ascompared to secondarycementum.

It is present in the apical 1/3rdand the interradicular area ofthe root.

It is cellular


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SECONDARY CEMENTUMFORMATION : Cementoblast first secrete

Collagen fibrils Non collagenous proteins

The collagen secreted is parallel tothe long axis of the root.

Then this matrix becomesmineralized but this time thecementoblast becomes trapped

within the cementum as lacunaes. These cementoblasts become

inactive and are known asCEMENTOCYTES.

Secondary cementum is alsoformed around the organizing PDLand partially mineralize them also.


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DEVELOPMEN T OF PERIODONTIUM

Where does the hertwigsroot sheath go ?

the cells after gettingfragmented form a basal laminaabout themselves and formislands of epithelial cells calledepithelial rest cells of Mallasezand they reside in the PDLclose to the cementum

they are resting cells or inactivecells since they have littlecytoplasm and dark staining(closed) nuclei.

There function is unknown butthey do decrease in number

with age.


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ALVEOLAR BONEFORMATION

New bone forms over thebony crypt in which the toothis developing to decreasethe space between the boneand the developing tooth

This bone is formed by cells

of the dental follicle. Formed in the same way as

cementum is formed, firstcollagen and non-collagenous proteins arelayed forming a fibrousfringe, then its mineralized.


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PERIODONTAL LIGAMENTFORMATION

The exact timing of ligamentformation varies in differenttooth types and betweenpermanent and deciduousteeth but the sequence is thesame which is as follows

l The space now between the

bone and cementum consistsof unorganized connectivetissue and has fibre bundlesinserted in it from both boneand cementum sides.


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PERIODONTAL LIGAMENT

FORMATION

The ligament fibroblastspresent in this connective tissuestart to form collagen fibres.

These collagen fibres becomeattached to the collagen fibrebundles coming from the boneand cementum to form longcontinues ligaments.

Later these fibres modify moreduring eruption and when theycome in occlusion.


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PERIODONTAL LIGAMENTORIENTATION1. First when the alveolar crest is above the cementoenamel junction the PDL are

oblique running from the bone downwards to the cementum2. Then when the tooth begins to erupt the cementoenamel junctions coincides

with the alveolar crest and the same set of PDL become horizontal.3. Finally when the tooth is fully erupted and comes into occlusion the same PDL

become oblique again but running from cementum to the bone downwards.


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DENTOGINGIVAL JUNCTIONFORMATION

Part of the gingiva facing the toothconstitutes part of the periodontium

It is an adaptation of the oralmucosa

It consists of the followingstructures

Junctional epithelium Sulcular epithelium

Gingival sulcus


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DENTOGINGIVAL JUNCTION FORMATION

To understand the process of dentogingival junction formation it isimportant to understand the following structures and the process oferuption The reduced dental epithelium the epithelial plug The epithelial cuff The primary epithelial attachment.


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REDUCED ENAMEL EPITHELIUM:

it is the epithelium overlying the tooth before it begins to erupt

Its has 2 layers an puter layer and an inner layer

Outer layer:consists of remnants of all the cells of the dentalorgan (stellate reticulum, stratum intermedium, etc.)

inner layer:consists of ameloblast which have completedthere function of enamel formation.

This epithelium along with the oral epithelium contribute informing the epithelial cuff.

Then later these cells form the junctional epithelium.


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EPITHELIAL PLUG

it is a mass of epithelial cells formed over the erupting toothbythe proliferation of the oral epithelial cellsfrom above and thereduced dental epithelial cellsbelow into the degeneratingconnective tissue.

Cell death in the middle of this plug leads to the formation of the

epithelial cuff.


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EPITHELIAL CUFF :

it is an epithelial canalformed at the time of eruption continueswith the oral epithelium above and the reduced dentalepithelium below to facilitate the movement of the tooth into theoral cavity.

It forms by cell death occuring in the middle of the epithelial

plug to form a canal.

It forms the sulcular epitheliumof the dentogingival junction.


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DENTOGINGIVAL JUNCTIONFORMATION

PRIMARY EPITHELIAL ATTACHMENT

The initial attachmentof the gingival epithelium tothe tooth surface when the tip of the toothemerges into the oral cavity iscalled the primaryepithelial attachment.

It is formed by the union of the cells of thegingival epitheliumand the reduced dentalepithelium.


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SEQUENCE OF EVENTS : After the tooth crown has been completely formed and before

the tooth eruption begins the space between the tooth and theoral epithelium consists of

Oral epithelium above

Connective tissue in the middle

The reduced dental epithelium over the tooth surface.

When the eruption begins the connective tissue in the middleof the epitheliums start to degenerate.

The outer layer of reduced dental epithelium and the basallayer of the oral epithelium starts to proliferate into thisdegenerating connective tissue to form the epithelial plug.


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SEQUENCE OF EVENTS : Cell death in the middle of this plug leads to formation of a

canal through which the tooth can erupt without hemmorhage.This canal is called the epithelial cuff.

Then when the tooth begins to erupt and the tip emerges outinto the oral cavity the attachment between the tooth surfaceand the oral epithelium is through the reduced dentalepithelium this is called the primary epithelial attachment.

Then this reduced dental epithelium is transformed into thejunctional epitheliumwhich consists of 2 layers

The squamous layer next to the tooth surface made out of theinner reduced dental epithelium (cannot divide)

The out basal layer made out of outer reduced dental epithelium(can divide)


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DEVELOPMENT OF PERIODONTIUMDENTOGINGIVAL JUNCTION FORMATION

SEQUENCE OF EVENTS : The epithelial cuff cells present above the junctional epithelium start

to proliferate into the junctional epithelium between the 2 layershence the nutritive supply of the inner squamous layer gets cut off

and they degenerate to form the gingival sulcus.

This leads to the formation of the sulcular epitheliumby the

epithelial cuff cells.


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SEQUENCE OF EVENTS :

Hence all the 3 structures are formed in this way

Dentogingival junction

Gingival sulcus Junctional epithelium Sulcular epithelium

Reduced dental epithelium Reduced dental epithelium Epithelial cuff


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LATER CHANGES :

the junctional epithelium derived from the reduced dental

epithelium is eventually replaced by the oral epithelial cellsdue to its high proliferation.

Passive eruption:

It is the apical migration of the dentogingival junction with

age it leads to increase in the length of the clinical crown.


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THE END

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