Development of the_periodontium

Development Of The PeriodontiumDevelopment Of The Periodontium

Development of the Development of the PeriodontiumPeriodontium


PeriodontiumPeriodontium is defined as those tissues is defined as those tissues supporting & investing the tooth. (Tencate 5supporting & investing the tooth. (Tencate 5 thth edi.) edi.)

It consists of :-It consists of :-

1. 1. CementumCementum (derived from the latin word (derived from the latin word caementum, quarried stone i.e. chips of stone used caementum, quarried stone i.e. chips of stone used in making mortar)in making mortar)


2.2. Periodontal ligament (PDL)Periodontal ligament (PDL)

3.3. Bone lining the alveolus (socket)Bone lining the alveolus (socket)

4.4. That part of the Gingiva facing That part of the Gingiva facing the tooththe tooth


GOMPHOSISGOMPHOSIS

(Socketed Tooth)(Socketed Tooth)

Relatively recent structure in evolutionary terms Relatively recent structure in evolutionary terms Almost exclusively mammalianAlmost exclusively mammalian


PERIODONTIUMPERIODONTIUM

Tissues of tooth support are odontogenic Tissues of tooth support are odontogenic Derived from dental follicleDerived from dental follicle Recent evidence indicating progenitor cells may be Recent evidence indicating progenitor cells may be

derived from cells of dental papilla that migrate into derived from cells of dental papilla that migrate into follicle at bell stage of developmentfollicle at bell stage of development


DENTAL FOLLICLEDENTAL FOLLICLE

Well defined layer of cells surrounding the tooth Well defined layer of cells surrounding the tooth germ that is continuous with & derived from the germ that is continuous with & derived from the dental papilla at the cervical loop.dental papilla at the cervical loop.

Dental follicle forms cementum, Periodontal Dental follicle forms cementum, Periodontal ligament & boneligament & bone


Functions of Dental Functions of Dental FollicleFollicle

To protect and stabilise the tooth during formation and To protect and stabilise the tooth during formation and later eruption.later eruption.

To provide nutrition and nerve supply to the developing To provide nutrition and nerve supply to the developing tooth.tooth.

To give rise to cells that form the cementum, the To give rise to cells that form the cementum, the periodontal ligament & the inner wall of the bony crypt periodontal ligament & the inner wall of the bony crypt or alveolus.or alveolus.


CryptCrypt A A cryptcrypt is a bony cavity enclosing a developing is a bony cavity enclosing a developing

tooth and is formed by the dental follicle.tooth and is formed by the dental follicle.

Each crypt has an opening in its roof through which Each crypt has an opening in its roof through which dental follicle fibres extend for communication within the dental follicle fibres extend for communication within the oral mucosa.oral mucosa.

The fibrous extension of the dental follicle, which The fibrous extension of the dental follicle, which connects the permanent tooth germ to the oral mucosa is connects the permanent tooth germ to the oral mucosa is

called called gubernacular cordgubernacular cord..


Dental Cementum Dental Cementum

The dynamic The dynamic tissue tissue

covering the covering the rootroot


Hyaline Layer of Hyaline Layer of Hopewell Smith / Hopewell Smith /

Intermediate Intermediate CementumCementum

It is a structure less highly mineralized layer It is a structure less highly mineralized layer some 10 um thick on the surface of the root some 10 um thick on the surface of the root dentin. Some investigators believe it may be a dentin. Some investigators believe it may be a form of enamel. form of enamel.


Hyaline Layer (HL)Hyaline Layer (HL) Many fish have teeth covered with enameloid ( a Many fish have teeth covered with enameloid ( a

tissue that resembles enamel but is partly formed tissue that resembles enamel but is partly formed by the dental papilla & internal dental epithelium)by the dental papilla & internal dental epithelium)

Enameloid & the hyaline layer are strikingly Enameloid & the hyaline layer are strikingly similar.similar.

It has been suggested that the function of HL is It has been suggested that the function of HL is to cement cementum to dentin.to cement cementum to dentin.


CEMENTOGENESISCEMENTOGENESIS

Cementum is deposited on the surface of root dentinCementum is deposited on the surface of root dentin

Hertwig’s epithelial root sheath initates the Hertwig’s epithelial root sheath initates the differentiation of root odontoblasts from the dental differentiation of root odontoblasts from the dental papilla, which then form dentin of the root.papilla, which then form dentin of the root.


Before primary cementum can form, root Before primary cementum can form, root sheath must fragment to allow follicular sheath must fragment to allow follicular cells to reach the newly formed root cells to reach the newly formed root surface.surface.

These follicular cells differentiate into These follicular cells differentiate into cementoblasts.cementoblasts.


Generally assumed that epithelium/ Generally assumed that epithelium/ epithelial product must be involved in epithelial product must be involved in initiating the differentiation of cementoblasts initiating the differentiation of cementoblasts from the dental follicle.from the dental follicle.

Eg:- When follicular tissue comes into Eg:- When follicular tissue comes into contact with enamel, cementum is deposited contact with enamel, cementum is deposited on the enamel surface. on the enamel surface.


Finally the epithelial derived product Finally the epithelial derived product (enamel like proteins) incorporated into the (enamel like proteins) incorporated into the hyaline layer may play a role in the hyaline layer may play a role in the differentiation of cementoblasts.differentiation of cementoblasts.


Cementoblasts insert cytoplasmic processes Cementoblasts insert cytoplasmic processes into unmineralised hyaline layer, begin to into unmineralised hyaline layer, begin to deposit collagen fibrils at right angles to the deposit collagen fibrils at right angles to the root surface.root surface.

Cementoblasts then migrate away from the Cementoblasts then migrate away from the hyaline layer but continue to deposit collagen hyaline layer but continue to deposit collagen forming the fibrous matrix of acellular forming the fibrous matrix of acellular cementum.cementum.


Cementoblasts also secrete noncollagenous Cementoblasts also secrete noncollagenous proteins such as bone sialoprotein and proteins such as bone sialoprotein and osteocalcin.osteocalcin.


ACELLULAR CEMENTUMACELLULAR CEMENTUM

This first formed cementum is acellular because the This first formed cementum is acellular because the cells retreat into the ligament.cells retreat into the ligament.

It covers at least coronal two thirds of the root.It covers at least coronal two thirds of the root.

This cementum thus consists of a mineralized layer This cementum thus consists of a mineralized layer with a fibrous fringe extruding from it.with a fibrous fringe extruding from it.


Once the tooth is in occlusion, a more rapidly formed Once the tooth is in occlusion, a more rapidly formed & less mineralized form is deposited around the & less mineralized form is deposited around the apical third of root.apical third of root.

The organic matrix consisting of noncollagenous The organic matrix consisting of noncollagenous proteins & collagen fibrils become mineralized as a proteins & collagen fibrils become mineralized as a result of cementoblasts budding off matrix vesicles.result of cementoblasts budding off matrix vesicles.


Cellular CementumCellular Cementum

At the same time, the cementoblasts get trapped in the At the same time, the cementoblasts get trapped in the matrix occupy lacunae & they become cementocytes. matrix occupy lacunae & they become cementocytes.

Thus this is called Thus this is called cellular cementumcellular cementum..

This cementum is confined to the apical third of the This cementum is confined to the apical third of the root & the interradicular regions of premolars & root & the interradicular regions of premolars & molars. molars.


FATE OF HERTWIG’S FATE OF HERTWIG’S ROOT SHEATHROOT SHEATH

As the sheath fragments & follicular cells migrate through As the sheath fragments & follicular cells migrate through it, however most of the cells persist as strands or clusters it, however most of the cells persist as strands or clusters

called as called as epithelial cell rests of malassezepithelial cell rests of malassez

These cells rests are remnants of the root sheath & are These cells rests are remnants of the root sheath & are seemingly discrete clusters or islands of epithelial cells.seemingly discrete clusters or islands of epithelial cells.


Cell Rests of Cell Rests of MalassezMalassez

They exhibit dark staining nuclei & little cytoplasm They exhibit dark staining nuclei & little cytoplasm & are inactive.& are inactive.

At present there is At present there is no functionno function for these cells, for these cells, however it has been suggested that they have a however it has been suggested that they have a protective function, preventing resorption of the root protective function, preventing resorption of the root surface to a role in maintaining the width of surface to a role in maintaining the width of periodontal ligament.periodontal ligament.


Alveolar Bone and the Alveolar Bone and the Alveolar Process Alveolar Process

( The socket that is ( The socket that is never stable)never stable)


ALVEOLAR BONE ALVEOLAR BONE FORMATIONFORMATION

As the root & its covering of primary cementum form, new As the root & its covering of primary cementum form, new bone is deposited against the crypt wall.bone is deposited against the crypt wall.

The deposition of this bone gradually reduces the space between The deposition of this bone gradually reduces the space between the crypt wall & tooth to the dimensions of periodontal the crypt wall & tooth to the dimensions of periodontal ligament.ligament.

As mentioned new bone is formed by osteoblasts originating As mentioned new bone is formed by osteoblasts originating from the dental follicle. from the dental follicle.


Development of the alveolar process begins Development of the alveolar process begins in the 8 in the 8thth week in utero. week in utero.

At that time, within the maxilla & At that time, within the maxilla & mandible the forming alveolar bone mandible the forming alveolar bone develops a horse shoe shaped groove that develops a horse shoe shaped groove that opens towards the oral cavity.opens towards the oral cavity.


The bony groove or canal is formed by The bony groove or canal is formed by growth of facial & lingual plates of the growth of facial & lingual plates of the body of maxilla & mandible & contains the body of maxilla & mandible & contains the developing tooth germs together with the developing tooth germs together with the alveolar vessels and nerves.alveolar vessels and nerves.

Initially the developing tooth germs lie in Initially the developing tooth germs lie in a groove.a groove.


Gradually bony septa develop between Gradually bony septa develop between teeth, so that each tooth is eventually teeth, so that each tooth is eventually contained in a separate crypt.contained in a separate crypt.

The alveolar process develops during the The alveolar process develops during the eruption of the teeth.eruption of the teeth.


During uterine life, the dental alveolus like During uterine life, the dental alveolus like the rest of skeleton is formed by an the rest of skeleton is formed by an embryonic type of bone composed of bony embryonic type of bone composed of bony spicules. spicules.

This embryonic bone - a variety of coarse This embryonic bone - a variety of coarse fibered or woven bone, is gradually fibered or woven bone, is gradually replaced by compact & spongy bone.replaced by compact & spongy bone.


Both compact & spongy bones initially are Both compact & spongy bones initially are composed of layers (lamellae) arranged in composed of layers (lamellae) arranged in an orderly manner.an orderly manner.

The alveolar bone proper is formed by the The alveolar bone proper is formed by the outermost cells of the dental follicle which outermost cells of the dental follicle which differentiate into osteoblasts.differentiate into osteoblasts.


They lay down the bony matrix or osteoid They lay down the bony matrix or osteoid in which some osteoblasts become in which some osteoblasts become

embedded as embedded as osteocytesosteocytes. .

The matrix then calcifies to form bone.The matrix then calcifies to form bone.


Periodontal Periodontal Ligament Ligament FormationFormation

The Periodontal ligament forms shortly after root The Periodontal ligament forms shortly after root formation begins.formation begins.

At the commencement of ligament formation the At the commencement of ligament formation the ligament space consists of unorganized connective ligament space consists of unorganized connective tissue with short fibre bundles extending into it from tissue with short fibre bundles extending into it from both cemental & bony surfaces.both cemental & bony surfaces.


Next ligament fibroblasts begin to form collagen Next ligament fibroblasts begin to form collagen which remodels to the collagen bundles & establish which remodels to the collagen bundles & establish continuity across the ligament space.continuity across the ligament space.

Thereby it secures the attachment of tooth Thereby it secures the attachment of tooth (cementum) to bone.(cementum) to bone.


Before the tooth erupts the crest of alveolar bone is Before the tooth erupts the crest of alveolar bone is above the CEJ & the developing fibre bundles of the above the CEJ & the developing fibre bundles of the PDL are all directed obliquely.PDL are all directed obliquely.

As the tooth moves coronally during eruption the As the tooth moves coronally during eruption the alveolar crest comes to coincide with the CEJ & the alveolar crest comes to coincide with the CEJ & the oblique fibre bundles become horizontally aligned.oblique fibre bundles become horizontally aligned.


When the tooth finally comes into function, alveolar When the tooth finally comes into function, alveolar crest is below the CEJ, thus the horizontal fibres crest is below the CEJ, thus the horizontal fibres

termed as termed as alveolar crest fibresalveolar crest fibres become oblique once more.become oblique once more.

Only after the teeth come into function do the fibre Only after the teeth come into function do the fibre bundles of PDL thicken appreciably. bundles of PDL thicken appreciably.


The ligament fibre bundles are established & The ligament fibre bundles are established & reoriented by the remodelling capacity of ligament reoriented by the remodelling capacity of ligament fibroblasts.fibroblasts.

The PDL achieves the The PDL achieves the highest ratehighest rate of of collagen remodelling & tissue turnover so far collagen remodelling & tissue turnover so far demonstrated. demonstrated.


The Gingival TissuesThe Gingival Tissues

The architecture ofThe architecture of

Periodontal Periodontal Protection Protection


Dento gingival Junction Dento gingival Junction FormationFormation

That part of the Gingiva facing the tooth is a part of That part of the Gingiva facing the tooth is a part of periodontium & it is an adaptation of the oral mucosa.periodontium & it is an adaptation of the oral mucosa.

At the time of eruption the crown of the tooth is At the time of eruption the crown of the tooth is covered by a double layer of epithelial cells. covered by a double layer of epithelial cells.


Those cells in contact with the enamel are ameloblasts, which Those cells in contact with the enamel are ameloblasts, which develop hemidesmosomes secrete a basal lamina & become develop hemidesmosomes secrete a basal lamina & become firmly attached to the enamel surface.firmly attached to the enamel surface.

The outer layer consists of more flattened cells the remnants of The outer layer consists of more flattened cells the remnants of all the remaining layers of dental organ.all the remaining layers of dental organ.

Together these 2 layers are called as Together these 2 layers are called as reduced reduced dental epithelium. dental epithelium.


Between the reduced enamel epithelium &the overlying oral Between the reduced enamel epithelium &the overlying oral epithelium is connective tissue which breaks down when the epithelium is connective tissue which breaks down when the tooth is erupting.tooth is erupting.

In response to degenerative changes in the connective tissues, In response to degenerative changes in the connective tissues, the cells of the outer layer of the reduced dental epithelium & the cells of the outer layer of the reduced dental epithelium & basal cells of the oral epithelium proliferate & migrate into the basal cells of the oral epithelium proliferate & migrate into the CT, eventually fusing to form a mass of epithelial cells over CT, eventually fusing to form a mass of epithelial cells over

the erupting tooth (the erupting tooth (epithelial cuffepithelial cuff).).


Thus the cells of the cuff are proliferative, migratory & Thus the cells of the cuff are proliferative, migratory & separated by widened intercellular spaces.separated by widened intercellular spaces.

Through these spaces, antigens enter from the oral cavity Through these spaces, antigens enter from the oral cavity leading to an acute inflammatory response within the leading to an acute inflammatory response within the connective tissue.connective tissue.

The clinical manifestation of this inflammatory response is The clinical manifestation of this inflammatory response is

called called TeethingTeething..


Once the cusp tip of erupting tooth emerges into the oral Once the cusp tip of erupting tooth emerges into the oral cavity, oral epithelial cells begin to migrate partially over the cavity, oral epithelial cells begin to migrate partially over the reduced enamel epithelium in an apical direction.reduced enamel epithelium in an apical direction.

At this time, the attachment of gingival epithelium to tooth is At this time, the attachment of gingival epithelium to tooth is maintained by ameloblasts & their hemidesmosomes & basal maintained by ameloblasts & their hemidesmosomes & basal lamina adjacent to the enamel surface. This is called lamina adjacent to the enamel surface. This is called

Primary Epithelial Attachment.Primary Epithelial Attachment.


A process of transformation takes place whereby the reduced A process of transformation takes place whereby the reduced

enamel epithelium gradually becomes enamel epithelium gradually becomes junctional junctional epitheliumepithelium..

The reduced ameloblasts which have lost their ability to divide The reduced ameloblasts which have lost their ability to divide get transformed into squamous epithelial cells.get transformed into squamous epithelial cells.


As the overgrowing epithelial cells from the cuff stratify, they As the overgrowing epithelial cells from the cuff stratify, they further separate the cells of the transformed dental epithelium further separate the cells of the transformed dental epithelium from the nutritive supply, with the latter cells degenerating & from the nutritive supply, with the latter cells degenerating &

creating a creating a Gingival SulcusGingival Sulcus . .

The final conversion of reduced dental epithelium to The final conversion of reduced dental epithelium to junctional epithelium may not occur until 3 to 4 years after the junctional epithelium may not occur until 3 to 4 years after the tooth has erupted.tooth has erupted.


Immediately after all the reduced dental epithelium has been Immediately after all the reduced dental epithelium has been transformed, the development of dentogingival junction may transformed, the development of dentogingival junction may be regarded as complete.be regarded as complete.

With the formation of the dentogingival junction, the dental With the formation of the dentogingival junction, the dental epithelium is finally lost.epithelium is finally lost.


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Development of the_periodontium

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