Period on Ti Um

8/2/2019 Period on Ti Um

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PERIODONTIUM

Oral HistologyDent 206


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Periodontium

Four tissue supporting the tooth in the jaw

Cementum

Periodontal ligament

Alveolar bone

Gingivae


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Cementum

Thin layer of calcified tissue covering the root inthe human teeth

Present in the crowns of some mammals

Adaptation to herbivorous diet

One of four tissues supporting the tooth(periodontium)

The least known ofPeriodontium tissues

All mineralized tissues


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Cementum

Varies in thickness

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

Thin cervically (10-15 m) Contiguous with PDL

Firmly adherent with root dentine

Highly responsive mineralized tissue Maintenance of root integrity

Maintenance of functional position oftooth

Tooth repair & regeneration


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Cementum

Slowly-formed throughout life

Allowing continual reattachment of PDL fibers

Cementum can be regarded as a mineralizedcomponent of PDL

Precementum - a thin mineralized layer on thesurface of the cellular cementum

Similar to bone, however -Avascular & not innervated

Less rapidly resorbedorthodontics


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Cement-enamel

junction

Pattern I

Cementum overlaps enamel for a short distance Most predominant60% of sections

Pattern II Enamel meet cementum at butt joint

Occurs in 30% of sections Pattern III

Enamel fails to meet cementum

Dentine between them is exposed

10% of sections


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Physical properties

Pale yellow

Softer than dentine

PermeabilityVaries with age and type of cementum

Decreases with age

Cellular is more permeable

More permeable than dentine Readily removed by abrasion after gingival

recession


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Chemical properties

Inorganic Organic Water

By weight 65% 23% 12%

By volume 45% 33% 22% Hydroxyapatite crystals similar to those in bone

More concentration of trace elements (F) at surface

F levels higher in acellular

Collagenous organic matrix, primarily type I

Molecules involved in PDL fiber reattachment &/ormineralization Bone sialoprotein, osteopontin & cementum-specific elements


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Classification of cementum

Presence or absence of cells

Cellular cementum

Acellular cementum

Nature & origin of organic matrix

Extrinsic fiber cementum

Intrinsic fiber cementum

Mixed fiber cementum

Combinations


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Acellular cementum

Most common pattern- adjacent to dentine

Structureless

Afibrillar cementumExists between

Acellular cementum

Hyaline layer (of Hopewell-Smith)

Mineralized GSCovers cervical enamel

Results following loss of REE


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Acellular cementum

Root dentine

Fibres of

Periodontal

Ligament

CementumEpithelial

Rests


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Cellular cementum

Most common patternApical area

Inter-radicular areas

Overlying acellular dentine

CementocytesInactive

In lacunaeappear dark in GSProcesses present in canaliculi

Processes connected via gap junctions


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Cellular cementum


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Cementocytes vs.

osteocytes

Cementocytes

More widely dispersed

Randomly arranged

Canaliculi oriented towardsPDLnutrition

Osteocytes

OsteonHaversian system

Organized cells

Circumferential lamellae


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Relationship between acellular &

cellular cementum

More common pattern

Acellularcervically

Acellular closer to dentine

Cellularapically

Cellular covers acellular

Less common patterns

Alternating

Acellular overlies cellular


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Extrinsic & intrinsic fiber cementum

Extrinsic fiber cementum

Fibers derived from inserting Sharpys fibers of PDL

Intrinsic fiber cementum

Run parallel to root surface at right angles toextrinsic fibers

Fibers derived from cementoblasts


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Acellular extrinsic fiber cementum

AEFC

Over cervical half2/3s of the root

Bulk of cementum in premolars

First formed cementum - acellular

Thickness of 15 m

All collagen are from Sharpys fibers

Though GS from cementoblasts

Fibers well-mineralized


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Cellular intrinsic fiber cementum

CIFC

Fibers deposited by cementoblasts

Fibers run parallel to root surface

No role of tooth attachment

In apical 1/3 & inter-radicular areas

May beTemporaryextrinsic fibers gain reattachment

Permanentwithout attaching fibers


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Acellular intrinsic fiber cemetum

If cementum forms slowly in CIFC


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Cellular mixed stratified cementum

Alternating AEFC with CIFC

Root apex

Furcation areas


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Mixed-fiber cementum

Collagen fibers derived fromExtrinsic fibers

Intrinsic fibers

Intrinsic fibers run between the extrinsic fibers Two typesrate of formation

Acellular mixed-fiber cementum

Well mineralized fibersCellular mixed-fiber cementum

Less well mineralized fibers


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Cemental incremental lines

Irregular rhythm of deposition

Not related to activity & quiescence

Related toDifference in the degree of mineralization

Composition of organic matrix

Imprecise periodicity

Acellularcloser, thinner & regular lines Cellular - farther apart, thicker & irregular lines


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Incremental lines

Cementum is formed rhythmically and can be

seen as being composed of layers


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Resorption & repair of cementum

Less susceptibility to resorption than bone

Localized resorption areas occur

Could be caused by microtrauma

May continue to root dentine

By multinucleated odontoclasts

Resorption filled by mineralized tissue(resembles cellular cementum)

Reversal line


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Reparative cementum vs. cementum

Wider uncalcified zone

Less mineralized

Smaller crystals Calcific globules are present

Differences are related to different speed of formation


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Clinical considerations

Cemental callus

Root fracture

No remodeling to original dimensions of the root

Cementicles

Free or attached pieces in PDL

Microtrauma

Apical & middle 1/3s of root

Root furcation


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Clinical considerations

Supra-eruption of teeth

Tooth wear

Local hypercementosis

Reaction to PA inflammation

Difficulty in extraction

Pagets disease multiple teeth withhypercementosis

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

Pulp removal in RCT up to that point


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Periodontal ligament PDL

Dense fibrous connective tissue

Occupies the area between the root of the tooth

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

Continuous with

the connective tissue of the gingiva above thealveolar crest

The dental pulp at the apical foramen


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Periodontal ligament space

Variable in width, average 0.2mm

looks hourglass in shape

Reduced in unerupted & non-functional teeth

Increased in teeth subjected

to heavy occlusal stress Narrows slightly with age

Narrower in permanent teeth


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Functions of PDL

Attachment

Has a role in tooth eruption and

support Its cells repair the alveolar bone &

cementum Neurological control of mastication

through its mechanoreceptors


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Components of PDL

Fibers

Ground substance

Cells


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Fibers of PDL

Collagen Type I (70% of fibers)

Type III (20% of fibers)

Found in the periphery of Sharpys fibers attachment into alveolar bone

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

Highest turnover of collagen is in PDL

Higher near apex

Even across the width of PDL

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

Attached into cementum

May have a role in tooth support


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Principal fibers of PDL

Fibers exist as bundles (principalfibers) running in differentorientations in different regionsDentoalveolar crest fibers

Horizontal fibers

Oblique fibersApical fibers

Interradicular fibers From crest of interradicular septum to

furcation


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Principal fibers of PDL


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Sharpys fibers

Principal fibersembedded intocementum and

bone

More numerous butsmaller at cemental

end Mineralized and

unmineralized parts


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Ground substance of PDL

60% of PDL by volume

Main componentsHyaluronate GAGs

ProteoglycansGlycoproteins

Functions of GS

Ion and water binding & exchangeControl of collagen fibrillogenesis & fiber

orientation

Tooth support & eruption - high tissue fluid

pressure


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Cells of PDL Fibroblasts

Fusiform cells with manyprocesses

Functionssecretion andturnover of fibers

Regeneration of tooth supportapparatus

Adaptive responses tomechanical loading

Cementoblasts Cement-forming cells lining

cemental surface Cuboidal cells

Osteoblasts Bone-forming cells lining

tooth socket Resemble cementoblasts


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Cells of PDL

Cementoclasts & osteoclasts

Resorbing cells

Howships lacunae

Epithelial rests cells Cuboidal cells that stain deeply

Close to cemental surface

Defence cells

Macrophages

Mast cells

Eosinophils


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Blood vessels of PDL

Separate from those entering pulp

Some from alveolar bone through foramina

Some from pulp through accessory canals

Major vessels lie between principal fiber bundle close toalveolar bone

Capillary plexus around the tooth

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

venous networks


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Innervation of PDL

Sensory

Nociception

Mechanoreception

Sensitivity to occlusal loads

Guidance to intercuspation

Autonomic

Associated with blood vessels


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Alveolar process

The alveolar process develops during theeruption of teeth

Grows at a rapid rate at the free border

Proliferates at the alveolar crest

No distinct boundary exists between the body ofthe maxilla or mandible and the alveolar process

If teeth are lost the alveolar bone disappears


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Development of bony crypt

Deciduous tooth &permanent successorinitially share crypt

Bone subsequently formsto encase permanenttooth

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Period on Ti Um

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