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Cementum and alveolar bone

Continued

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Cementum

The other bone

It is a hard avascular connectivetissue that covers the roots ofteeth

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Calcified mesenchymal tissue that forms

the outer covering of the anatomic root

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Cementum componentsCELLS

Cementoblasts

Cementocytes

Cementoclasts

MATRIXWater 12%

Inorganic minerals 61%

Organic materials 27%

cementum is the least mineralized of thehard dental tissues, it is moremineralized than bone which is just 45%mineralized

FIBRES

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Role 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

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Varies in thickness:

thickest in the apexandIn the inter-radicular

areas of multirootedteeth, and thinnest inthe cervical area

10 to 15 microns inthe cervical areas to50 to 200 microns

(can exceed > 600

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Cementum

What are the sources of collagen fibers in

cementum?

Extrinsic sharpeys fibers formed by

Fibroblasts.

Intrinsic Fibers of the cementum matrix

formed by cement oblasts.

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Extrinsic Fibers

- Constitute a considerable

proportion of the bulk

of

Cementum.

- The embedded portion of the

principal fibers of theperiodontal ligament.

- Formed by the fibroblasts

- Composed of mainly collagen

type I, coated by collagen typeIII.The insertion of sharpys fibers into the

cementum

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Intrinsic fibers

Belong to the

cementum matrixProduced by

cementoblasts

cementocytes

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Differences between

cementum and bone

Not vascularized a reason for itbeing resistant to resorption Minor ability to remodel

More resistant to resorptioncompared to bone Lacks neural component so nopain 70% of bone is made by inorganicsalts (cementum only 45-50%) 2 unique cementum molecules:

Cementum attachment protein

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Clinical Correlation

Cementum is more resistant

to resorption: Important inpermittingorthodontic tooth movement

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Development of Cementum

Cementum formation occurs along theentire tooth

Hertwigs epithelial root sheath (HERS) Extension of the inner and outer dentalepitheliumHERS sends inductive signal to ectomesen-

chymal pulp cells to secrete predentin bydifferentiating into odontoblastsHERS becomes interruptedEctomesenchymal cells from the innerportionof the dental follicle come in withpredentin bydifferentiating into cementoblastsCementoblasts lay down cementum

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How cementoblasts get activated to lay down

cementum is not known

2 theories:

1. Infiltrating dental follicle cells receive

reciprocal signal fromthe dentin or the surrounding HERS cellsand differentiate into cementoblasts

2. HERS cells directly differentiate intocementoblasts

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Cementoblasts

Derive from dental follicle

Transformation of epithelialcells

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Proteins associated withCementogenesis

Growth factors

TGF- transforming growth factor

PDGF -platelet-derived growth factor

-FGF fibroblast growth factor

Adhesion molecules

Bone sialoprotein

Osteopontin

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Proteins associated with

Cementogenesis

Epithelial/enamel-like factors

Collagens

Gla proteinsMatrix

Bone

Transcription factors

Cbfa 1 and osterixis an essential transcription factor forosteoblast differentiation and boneformation

Other

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First layer of cementum isactually formed by the inner

cells of the HERS and isdeposited on the rootssurface is called intermediatecementum or Hyaline layer ofHopewell-Smith

Deposition occurs before theHERS disintegrates. Seals ofthe dentin

Intermediate cementum issituated between the

granular dentin layer ofTomes and the secondarycementum that is formed bythe cementoblasts (whicharise from the dental follicle)

Hyaline layer of Hopewell-Smith (Intermediate Cementum

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Properties of Cementum

Physical: Cementum is pale yellow with a dull

surface

Cementum is more permeable than other dental

tissuesRelative softness and the thinness at the

cervical portion means that cementum is readily

removed by the abrasion when gingivalrecession exposes the root surface to the oral

environment

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Chemical Composition of Cementum

Similar to bone

45% to 50% hydroxyapatite (inorganic)

50% to 55% collagenous and noncollagenous matrixproteins

(organic)

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Classification ofCementum

Presence or absence of cells

Origin of collagenous fibers of the matrix

Prefunctional and functional

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Cellular and Acellular Cementum

A: Acellular cementum (primary cementum)

B: Cellular Cementum (secondary cementum)

Acellular cementum: covers the

rootadjacent to dentin whereascellularcementum is found in the apicalarea

Cellular: apical area andoverlyingacellular cementum. Alsocommon ininterradicular areas

Cementum is more cellular asthethickness increases in order tomaintain

Viability

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A: Acellular cementum

B: Hyaline layer of Hopwell-Smith

C: Granular layer of Tomes

D: Root dentin

Cellular: Has cellsAcellular: No cells and has no structure

Cellular cementum usually overlies acellular cementum

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Acellular

Cellular

Variations also noted where acellular and cellular reverse in position

and also alternate

CEMENTUM

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Dentin

Lacuna of cementocyte

Canaliculus

CEMENTUM

Acellular cementum

Cellular cementum

Hyaline layer(of Hopewell Smith)

Granular layer of tomes

Dentin with tubules

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Cementoblast and cementocyte

Cementocytes in lacunae and the channels that their processes extend are

called the canaliculi

Cementoid: Young matrix that becomes secondarily mineralized

Cementum is deposited in increments similar to bone and dentin

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Are acellular and cellular cementum formed from two

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Are acellular and cellular cementum formed from twodifferent sources?

heory is that the structural differences between acellular andntum is related to the faster rate of matrix formation for cellul

ntum. Cementoblasts gets incorporated and embedded in thementocytes.

rent rates of cementum formation also reflected in more wideld incremental lines in cellular cementum

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ification Based on the Nature and Origin of Collagen

nic matrix derived form 2 sources:

riodontal ligament (Sharpeys fibers)mentoblasts

nsic fibers derived from PDL. These are in the same

tion of the PDL principal fibers perpendicular orue to the root surface

sic fibers derived from cementoblasts. Run paralleoot surface and at right angles to the extrinsic fiber

rea where both extrinsic and intrinsic fibers is called fiber cementum

Combined classification

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Combined classification

Acellular Extrinsic Fiber Cementum (AEFC-PrimaryCementum)

Located in cervical half of the root andconstitutes the bulk of cementum

The collagen fibers derived from Sharpeys fibers

and ground substance from cementoblasts

Covers 2/3rds of root corresponding with thedistribution of primary acellular cementum

Principal tissue of attachment

Function in anchoring of tooth

Fibers are well mineralized

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Cellular intrinsic fiber cementum(CIFC-Secondary Cementum(

Starts forming after the tooth is in occlusionIncorporated cells with majority of fibers organized

parallel to the root surface

Cells have phenotype of bone forming cells

Very minor role in attachment (virtually absent in

incisors and canine teeth)

Corresponds to cellular cementum and is seen in

middle to apical third and intrerradicularAdaptation

Repair

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Secondary cellular mixed fibercementum

Both intrinsic and extrinsic fibers]Extrinsic (5 7 microns) and Intrinsic

(1 2 microns)[Bulk of secondary cementum

CementocytesLaminated structure

Cementoid on the surfaceApical portion and intrerradicular

Adaptation

Intrinsic fibers are uniformlymineralized but the extrinsic fibers

are variably mineralized with somecentral unmineralized cores

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Acellular afibrillar cementum

Limited to enamel surfaceClose to the CE junction

Lacks collagen so plays no role in attachment

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Distribution of Cementum on the Root

Acellular afibrillar: cervical enamel

Acellular extrinsic: Cervix to practically

the whole root (incisors, canines)

increasing in thickness towards the

apical portion 50200 microns

Cellular: Apical third, furcations

A i f C t

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Aging of Cementum

. Smooth surface becomes irregular due

to calcification of ligament fiber bundles

where they are attached to cementum

. Continues deposition of cementum occurs

with age in the apical area.

]Good: maintains tooth length; bad:

obstructs the foramen

. Cementum resorption.Active for a period

of time and then stops for cementumdeposition creating reversal lines

. Resorption of root dentin occurs with aging

which is covered by cemental repair

Cementicles

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Cementicles

Calcified ovoid or round nodule

found in the PDL Single or multiple near the cemental

surface Free in ligament; attached or

embedded in cementum

Aging and at sites of traumaOrigin: Nidus of epithelial cell that are

composed of calcium phosphate and

collagen to the same amount as

cementum (45% to 50% inorganicand 50% to 55% organic)

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Cemental Repair

Protective function of cementoblasts after

resorption of root dentin or cementum

Resorption of dentin and cementum due

to trauma (traumatic occlusion, tooth

movement, hypereruption)

Loss of cementum accompanied by lossof attachment

Following reparative cementum

deposition attachment is restored

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Clinical Correlation

Cellular cementum is similar to bone but has nonerves.Therefore it is non-sensitive to pain. Scalingproduces

no pain, but if cementum is removed, dentin isexposedcauses sensitivity

Cementum is resistant to resorption especially inyoungerPatients. Thus, orthodontic tooth movementcauses alveolarbone resorption and not tooth root loss

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TOOTH TISSUES: CEMENTUM

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TOOTH TISSUES: CEMENTUM

ALVEOLAR BONE

PULP

DENTINE

ENAMEL

CEMENTUM

PERIODONTAL

LIGAMENT/ PDL

GINGIVA

CEMENTUM: Position

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PULP

DENTINE

CEMENTUM

CEMENTUM: Position

ENAMELCROWN

Cervix

ROOT

}}

Cementum is on the root, but can extend slightly

onto enamel. Cementum also can be exposed to

the oral cavity, if the gingiva recedes too far

INTER-RADICULAR CEMENTUM

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Multi-rooted teeth usually

have particularly thick &

cellular cementumbetween the roots in an

inter-radicularposition

INTER-RADICULAR CEMENTUM

CEMENTUM: Boundaries

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CEMENTUM: Boundaries

Cemento-enamel junction CEJ

Dentino-cemental junction DCJ

Ligamento-cemental junction

APICAL FORAMEN

GROWTH OF CEMENTUM = PDL anchoring

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E

D

E

D

Reactivated cementoblasts

lay downcementoid

E

D

E

D

GROWTH OF CEMENTUM PDL anchoring

Cementoid becomes

another layer ofcementum.

Cells make more cementoid

PDL

fibers

PDL fibers become

imbedded in newly

formed cementum

-Sharpeys fibers

SEQUENCES

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Dentine formed before

cementum

& cervical before apical

Directions of

cemental

growth -

outwards &

apicalwards

SEQUENCES

CEMENTICLES

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P

UL

P

CEMENTICLES

Hard mineralized bodies found in

the periodontal ligament or

partially imbedded in cementum

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.Alveolar Bone

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Alveolar Bone

Osseous tissue is rigid connective tissue that

is normally organized into definite

structures termed bone.The alveolar process is defined as the parts

of the maxilla and the mandible that form

and support the sockets of the teeth

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Alveolar bone:

1-alveolar bone proper

2-trabecular bone

3-compact bone.

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The Alveolar Process Consist Of

1-Inner and outer

cortical Plate

Compact Bone(

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1-compact bone include:

a-The Haversian canal

b-Volk-manns

canalsblood supply(

c- Lamella and

osteocyte in lacunae.

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2-Cancellous bone spongy(:

spongy Bone:-Between the two compact layers

-Consist of trabeculae that enclose marrow

spaces.

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3-The alveolar bone proper:

Bone lines the socket and extends over the

alveolar crest often appears as a radiodense

line, termed the lamina dura.

-Other term Bundle bone.

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Composition of Alveolar Bone

1-The cellsosteoblast,osteoclast and

osteocytes(.

2-Extra-cellular matrix consists of two-thirds

inorganic matter and one third

organic matrix.

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CELLS OF ALVEOLAR BONE

Calcified matrix with osteocytes enclosed in lacunae

Constantly changing

Osteoblasts deposit

Osteoclasts resorb

Matrix deposited by osteoblasts is not mineralized and is

termed osteoid. As new osteoid is deposited the old osteoid

mineralizes.

Osteoclasts are large multinucleated cells that are often on

surface or in Howships lacunae. Main function is resorption

of bone.

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The inorganic matrix is composed of the

minerals calcium and phosphate,

The organic matrix consists mainly 90%( of

collagen type I, with small amounts of non

collagenous proteins

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The cortical plates and the bone lining of the

socket meet at the alveolar crest, usually

2mm below the cementoenamel junction.

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Summary:

Periodontium consists of 4 different tissues:

Gingiva

Cementum

PDL

Alveolar bone

They are anatomically separated, but

functionally , they all depends on each other

in maintaining a viable healthy supportingstructure for the tooth.

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Have a nice future perio patient!