PERIODONTIUMPERIODONTIUM

Oral mic anatomy and embyrologyBEE

PERIODONTIUM

Cementum

PDL

Alveolar bone

Sharpey's fibers

Attachmentorgan

Cementum

Periodontalligament

Alveolar bone

Apical foramen

Pulp cavityEnamelDentin

Gingiva

Root canal

Alveolar vessels& nerves

TEETH IN-SITU

PeriodontiumPeriodontium

Four tissue supporting the tooth in the jaw◦Cementum◦Periodontal ligament◦Alveolar bone◦Gingivae

CementumCementum

Thin layer of calcified tissue covering the root in the human teeth

Present in the crowns of some mammals◦Adaptation to herbivorous diet

One of four tissues supporting the tooth (periodontium)

The least known of ◦Periodontium tissues◦All mineralized tissues

Role of CementumRole of Cementum

1) It covers and protects the root dentin (covers the opening of dentinal tubules)

2) It provides attachment of the periodontal fibers

3) It reverses tooth resorption

CementumCementum

Varies in thickness◦Thick @ apex (50-200 µm) &

inter-radicular regions◦Thin cervically (10-15 µm)

Contiguous with PDLFirmly adherent with root

dentineHighly responsive mineralized

tissue◦Maintenance of root integrity◦Maintenance of functional

position of tooth◦Tooth repair & regeneration

Varies in thickness: thickest in the apex andIn the inter-radicular areas of multirootedteeth, and thinnest in the cervical area

10 to 15 m in the cervical areas to50 to 200 m (can exceed > 600 m) apically

CementumCementum

Slowly-formed throughout lifeAllowing continual reattachment of PDL

fibersCementum can be regarded as a

mineralized component of PDLPrecementum - a thin mineralized layer on

the surface of the cellular cementumSimilar to bone, however -

◦Avascular & not innervated◦Less rapidly resorbed – orthodontics

Cement-Cement-enamel enamel junctionjunction

Pattern I◦Cementum overlaps enamel for a short distance◦Most predominant – 60% 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

Physical propertiesPhysical properties

Pale yellowSofter than dentinePermeability

◦Varies with age and type of cementum◦Decreases with age◦Cellular is more permeable◦More permeable than dentine

Readily removed by abrasion after gingival recession

Chemical propertiesChemical properties

InorganiInorganicc

OrganicOrganic WaterWater

By By weightweight

65%65% 23%23% 12%12%

By By volumevolume

45%45% 33%33% 22%22%Hydroxyapatite crystals similar to those in boneMore concentration of trace elements (F) at

surfaceF levels higher in acellularCollagenous organic matrix, primarily type IMolecules involved in PDL fiber reattachment &/or

mineralization◦ Bone sialoprotein, osteopontin & cementum-specific

elements

Cellular and Acellular Cementum

A: Acellular cementum (primary cementum)B: Cellular Cementum (secondary cementum)

Acellular cementum: covers the rootadjacent to dentin whereas cellularcementum is found in the apical area

Cellular: apical area and overlyingacellular cementum. Also common ininterradicular areas

Cementum is more cellular as thethickness increases in order to maintainViability

The thin cervical layer requires no cellsto maintain viability as the fluids batheits surface

A: Acellular cementumB: Hyaline layer of Hopwell-SmithC: Granular layer of TomesD: Root dentin

Cellular: Has cellsAcellular: No cells and has no structure

Cellular cementum usually overlies acellular cementum

Acellular

Cellular

Variations also noted where acellular and cellular reverse in position and also alternate

Dentin

GT

Lacuna of cementocyte

Canaliculus

CEMENTUM

Acellular cementumCellular cementumHyaline layer (of Hopewell Smith)Granular layer of tomes

Dentin with tubules

Cementoblast and cementocyte

Cementocytes in lacunae and the channels that their processes extend arecalled the canaliculi

Cementoid: Young matrix that becomes secondarily mineralized

Cementum is deposited in increments similar to bone and dentin

Are acellular and cellular cementum formed from two different sources?

One theory is that the structural differences between acellular and cellularcementum is related to the faster rate of matrix formation for cellularcementum. Cementoblasts gets incorporated and embedded in the tissueas cementocytes.

Different rates of cementum formation also reflected in more widelyspaced incremental lines in cellular cementum

Classification of cementumClassification 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

Acellular cementumAcellular cementum

Most common pattern- adjacent to dentine

StructurelessAfibrillar cementum

◦Exists between Acellular cementum Hyaline layer (of Hopewell-Smith)

◦Mineralized GS◦Covers cervical enamel◦Results following loss of REE

Acellular cementumAcellular cementum•Root dentine

•Fibres of Periodontal Ligament

•Cementum•Epithelial Rests

Cellular cementumCellular cementum

Most common pattern◦Apical area◦Inter-radicular areas◦Overlying acellular dentine

Cementocytes◦Inactive◦In lacunae – appear dark in GS◦Processes present in canaliculi◦Processes connected via gap junctions

Cellular cementumCellular cementum

Cementum simulates boneCementum simulates bone

Organic fibrous framework, ground substance, crystal type, development Lacunae Canaliculi Cellular component Incremental lines (also known as “resting”

lines; they are produced by continuous butphasic, deposition of cementum)

Clinical Correlation

Cementum is more resistant to resorption: Important in permittingorthodontic tooth movement

Cementocytes vs. Cementocytes vs. osteocytesosteocytes

Cementocytes◦More widely dispersed◦Randomly arranged◦Canaliculi oriented towards

PDL – nutritionOsteocytes

◦Osteon – Haversian system◦Organized cells◦Circumferential lamellae

Relationship between acellular Relationship between acellular & cellular cementum& cellular cementum

More common pattern◦Acellular – cervically◦Acellular closer to dentine◦Cellular – apically◦Cellular covers acellular

Less common patterns◦Alternating◦Acellular overlies cellular

Extrinsic & intrinsic fiber Extrinsic & intrinsic fiber cementumcementum

Extrinsic fiber cementum◦Fibers derived from inserting Sharpy’s fibers of

PDLIntrinsic fiber cementum

◦Run parallel to root surface at right angles to extrinsic fibers

◦Fibers derived from cementoblasts

Acellular extrinsic fiber Acellular extrinsic fiber cementumcementum

AEFCOver cervical half – 2/3s of the rootBulk of cementum in premolarsFirst formed cementum - acellularThickness of 15 µmAll collagen are from Sharpy’s fibersThough GS from cementoblastsFibers well-mineralized

Cellular intrinsic fiber cementumCellular intrinsic fiber cementum

CIFCFibers deposited by cementoblastsFibers run parallel to root surfaceNo role of tooth attachmentIn apical 1/3 & inter-radicular areasMay be

◦Temporary – extrinsic fibers gain reattachment◦Permanent – without attaching fibers

Acellular intrinsic fiber cemetumAcellular intrinsic fiber cemetum

If cementum forms slowly in CIFC

Cellular mixed stratified Cellular mixed stratified cementumcementum

Alternating AEFC with CIFCRoot apexFurcation areas

Mixed-fiber cementumMixed-fiber cementum

Collagen fibers derived from◦Extrinsic fibers◦Intrinsic fibers

Intrinsic fibers run between the extrinsic fibers

Two types – rate of formation◦Acellular mixed-fiber cementum

Well mineralized fibers◦Cellular mixed-fiber cementum

Less well mineralized fibers

Cemental incremental linesCemental incremental lines

Irregular rhythm of depositionNot related to activity & quiescence Related to

◦Difference in the degree of mineralization◦Composition of organic matrix

Imprecise periodicityAcellular – closer, thinner & regular linesCellular - farther apart, thicker & irregular

lines

Development of CementumCementum formation occurs along theentire tooth

Hertwig’s epithelial root sheath (HERS) –Extension of the inner and outer dentalepithelium

HERS sends inductive signal to ectomesen-chymal pulp cells to secrete predentin bydifferentiating into odontoblasts

HERS becomes interrupted

Ectomesenchymal cells from the inner portionof the dental follicle come in with predentin bydifferentiating into cementoblasts

Cementoblasts lay down cementum

How cementoblasts get activated to lay downcementum is not known

3 theories:

1. Infiltrating dental follicle cells receive reciprocal signal fromthe dentin or the surrounding HERS cells and differentiateinto cementoblasts

2. HERS cells directly differentiate into cementoblasts

3. What are the function of epithelial cell rests of Malassez?

CementoblastsCementoblasts

Derive from dental follicleTransformation of epithelial cells

Incremental linesIncremental lines

Cementum is formed rhythmically and can be seen as being composed of layers

Resorption & repair of cementumResorption & repair of cementum

Less susceptibility to resorption than boneLocalized resorption areas occurCould be caused by microtraumaMay continue to root dentineBy multinucleated odontoclastsResorption filled by mineralized tissue

(resembles cellular cementum)Reversal line

Reparative cementum vs. Reparative cementum vs. cementumcementum

Wider uncalcified zoneLess mineralizedSmaller crystalsCalcific globules are present

Differences are related to different speed of formation

Clinical considerationsClinical considerations

Cemental callus◦Root fracture◦No remodeling to original dimensions of the

rootCementicles

◦Free or attached pieces in PDL◦Microtrauma◦Apical & middle 1/3s of root◦Root furcation

Clinical considerationsClinical considerations

Supra-eruption of teethTooth wearLocal hypercementosis

◦Reaction to PA inflammation◦Difficulty in extraction◦Paget’s disease – multiple teeth

with hypercementosisCementum narrowing root

canal and shifting the junction between dental pulp & PDL cervically◦Pulp removal in RCT up to that

point

Periodontal ligament PDLPeriodontal ligament PDL

Dense fibrous connective tissueOccupies the area between the root of the

tooth and the walls of the alveolar socketDerived from the dental follicleContinuous with

◦the connective tissue of the gingiva above the alveolar crest

◦The dental pulp at the apical foramen

Periodontal ligament Periodontal ligament spacespace

Variable in width, average 0.2 mm

looks hourglass in shapeReduced in unerupted &

non-functional teethIncreased in teeth

subjected to heavy occlusal stress

Narrows slightly with age

Narrower in permanent teeth

Functions of PDLFunctions of PDL

AttachmentHas a role in tooth eruption and support

Its cells repair the alveolar bone & cementum

Neurological control of mastication through its mechanoreceptors

Components of PDLComponents of PDL

FibersGround substanceCells

Fibers of PDLFibers of PDL

Collagen◦ Type I (70% of fibers)◦ Type III (20% of fibers)

Found in the periphery of Sharpy’s 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

Principal fibers of PDLPrincipal fibers of PDL

Fibers exist as bundles (principal fibers) running in different orientations in different regions◦Dentoalveolar crest fibers◦Horizontal fibers◦Oblique fibers◦Apical fibers◦Interradicular fibers

From crest of interradicular septum to furcation

Principal fibers of PDLPrincipal fibers of PDL

Sharpy’s fibersSharpy’s fibers

Principal fibers embedded into cementum and bone

More numerous but smaller at cemental end

Mineralized and unmineralized parts

Ground substance of Ground substance of PDLPDL

60% of PDL by volumeMain components

◦Hyaluronate GAGs◦Proteoglycans◦Glycoproteins

Functions of GS◦Ion and water binding & exchange◦Control of collagen fibrillogenesis & fiber

orientation◦Tooth support & eruption - high tissue fluid

pressure

Cells of PDLCells of PDLFibroblasts

◦Fusiform cells with many processes

◦Functions – secretion and turnover of fibers Regeneration of tooth

support apparatus Adaptive responses to

mechanical loadingCementoblasts

◦Cement-forming cells lining cemental surface

◦Cuboidal cellsOsteoblasts

◦Bone-forming cells lining tooth socket

◦Resemble cementoblasts

Cells of PDLCells of PDL

Cementoclasts & osteoclasts◦Resorbing cells◦Howship’s lacunae

Epithelial rests cells◦Cuboidal cells that stain deeply◦Close to cemental surface

Defence cells◦Macrophages◦Mast cells◦Eosinophils

Blood vessels of PDLBlood vessels of PDL

Separate from those entering pulpSome from alveolar bone through foraminaSome from pulp through accessory canalsMajor vessels lie between principal fiber

bundle close to alveolar boneCapillary plexus around the toothCrevicular plexus of capillary loopsVeins do not follow arteries but drain into

intraalveolar venous networks

Innervation of PDLInnervation of PDL

Sensory◦Nociception◦Mechanoreception

Sensitivity to occlusal loads Guidance to intercuspation

Autonomic◦Associated with blood vessels

Alveolar processAlveolar process

The alveolar process develops during the eruption of teeth

Grows at a rapid rate at the free borderProliferates at the alveolar crestNo distinct boundary exists between the

body of the maxilla or mandible and the alveolar process

If teeth are lost the alveolar bone disappears

Development of bony cryptDevelopment of bony crypt

Deciduous tooth & permanent successor initially share crypt

Bone subsequently forms to encase permanent tooth