14 periodontium

7/28/2019 14 Periodontium

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PERIODONTIUM

Cementum

PDL

Alveolar bone

Sharpey's fibers

Attachmentorgan

Cementum

Periodontal

ligament

Alveolar bone

Apical foramen

Pulp cavityEnamel

Dentin

Gingiva

Root canal

Alveolar vessels

& nerves


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TEETH IN-SI TU


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Periodontium (forms a

specialized fibrous joint called

Gomphosis)

Cementum

Periodontal Ligament

Alveolar bone

Gingiva facing the tooth


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Cementum

The other bone

It is a hard avascular connectivetissue that covers the roots of

teeth


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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 to the

periodontal fibers

3) It compensates for tooth resorption


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Varies in thickness: thickest in the apex andin the inter-radicular areas of multirooted

teeth, and thinnest in the cervical area

10 to 15 m in the cervical areas to

50 to 200 m (can exceed > 600 m) apically


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Cementum simulates bone

Organic fibrous framework, ground

substance, crystal type, development

Lacunae Canaliculi

Cellular component

Incremental lines (also known as restinglines; they are produced by continuous but

phasic, deposition of cementum)


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Differences between cementum

and bone

Not vascularized a reason for it being resistant

to resorption

Minor ability to remodel

More resistant to resorption compared to bone

Lacks neural component so no pain

70% of bone is made by inorganic salts(cementum only 45-50%)

2 unique cementum molecules: Cementum

attachment protein (CAP) and IGF


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Clinical Correlation

Cementum is more resistant to resorption: Important in permitting

orthodontic tooth movement


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Development of Cementum

Cementum formation occurs along the

entire tooth

Hertwigs epithelial root sheath (HERS)

Extension of the inner and outer dental

epithelium

HERS sends inductive signal to ectomesen-chymal pulp cells to secrete predentin by

differentiating into odontoblasts

HERS becomes interrupted

Ectomesenchymal cells from the inner portion

of the dental follicle come in with predentin by

differentiating into cementoblasts

Cementoblasts lay down cementum


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How cementoblasts get activated to lay down

cementum is not known

3 theories:

1. Infiltrating dental follicle cells receive reciprocal signal from

the dentin or the surrounding HERS cells and differentiate

into cementoblasts

2. HERS cells directly differentiate into cementoblasts

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


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Cementoblasts

Derive from dental follicle

Transformation of epithelial cells


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Proteins associated with

Cementogenesis

Growth factors

TGF

PDGF FGF

Adhesion molecules

Bone sialoprotein Osteopontin


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First layer of cementum is actually

formed by the inner cells of the HERS

and is deposited on the roots surfaceis called intermediate cementum or

Hyaline layer of Hopewell-Smith

Deposition occurs before the HERS

disintegrates. Seals of the dentinal

tubules

Intermediate cementum is situated

between the granular dentin layer of

Tomes and the secondary cementum

that is formed by the cementoblasts

(which arise from the dental follicle)

Approximately 10 m thick and

mineralizes greater than the adjacent

dentin or the secondary cementum

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 tissues

Relative softness and the thinness at the cervical portion means

that cementum is readily removed by the abrasion when gingival

recession 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 matrix proteins

(organic)


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Collagenous component

TYPE I TYPE III

TYPE XII TYPE V

TYPE XIV


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Classification of Cementum

Presence or absence of cells

Origin of collagenous fibers of thematrix

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 root

adjacent to dentin whereas cellularcementum is found in the apical area

Cellular: apical area and overlying

acellular cementum. Also common in

interradicular areas

Cementum is more cellular as the

thickness increases in order to maintain

viability

The thin cervical layer requires no cells

to maintain viability as the fluids bathe

its surface


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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


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Dentin

GT

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 different

sources?

One theory is that the structural differences between acellular and cellular

cementum is related to the faster rate of matrix formation for cellularcementum. Cementoblasts gets incorporated and embedded in the tissue

as cementocytes.

Different rates of cementum formation also reflected in more widely

spaced incremental lines in cellular cementum


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Classification Based on the Nature and Origin of Collagen Fibers

Organic matrix derived form 2 sources:

1. Periodontal ligament (Sharpeys fibers)2. Cementoblasts

Extrinsic fibers if derived from PDL. These are in the same

direction of the PDL principal fibers i.e. perpendicular oroblique to the root surface

Intrinsic fibers if derived from cementoblasts. Run parallel to

the root surface and at right angles to the extrinsic fibers

The area where both extrinsic and intrinsic fibers is called

mixed fiber cementum


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Combined classification (see Table 9-2)

Acellular Extrinsic Fiber Cementum (AEFC-Primary Cementum)

Located in cervical half of the root and constitutes the bulk of cementum

The collagen fibers derived from Sharpeys fibers and ground substance

from cementoblasts

Covers 2/3rds of root corresponding with the distribution of primaryacellular cementum

Principal tissue of attachment

Function in anchoring of tooth

Fibers are well mineralized


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Primary acellular intrinsic fiber

First cementum

Primary cementum

Acellular

Before PDL forms

Cementoblasts

15-20m


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Cellular intrinsic fiber cementum (CIFC-

Secondary Cementum )

Starts forming after the tooth is in occlusion Incorporated 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 inincisors and canine teeth)

Corresponds to cellular cementum and is seen in

middle to apical third and intrerradicular

Adaptation Repair


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Secondary cellular mixed fiber cementum

Both intrinsic and extrinsic fibers

[Extrinsic (5 7 m) and Intrinsic (1 2 m)] Bulk of secondary cementum

Cementocytes

Laminated structure

Cementoid on the surface

Apical portion and intrerradicular Adaptation

Intrinsic fibers are uniformly mineralized but the extrinsic fibers arevariably mineralized with some central unmineralized cores


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Zone of Transition


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Acellular afibrillar cementum

Limited to enamel surface Close to the CE junction

Lacks collagen so plays no role in attachment

Developmental anomaly vs. true product of epithelial

cells


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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 50200m

Cellular: Apical third, furcations


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CE junctionThe OMG rule

Cementum overlaps enamel 60%

Cementum just meets enamel 30%

Small gap between cementum and enamel 10%


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Aging of Cement m


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Aging of Cementum

1. Smooth surface becomes irregular due

to calcification of ligament fiber bundles

where they are attached to cementum

2. Continues deposition of cementum occurswith age in the apical area.

[Good: maintains tooth length; bad:

obstructs the foramen]

3. Cementum resorption. Active for a period

of time and then stops for cementum

deposition creating reversal lines

4. Resorption of root dentin occurs with aging

which is covered by cemental repair

C


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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 trauma

Origin: Nidus of epithelial cell that are

composed of calcium phosphate and

collagen to the same amount as

cementum (45% to 50% inorganic

and 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 no nerves.Therefore it is non-sensitive to pain. Scaling produces

no pain, but if cementum is removed, dentin is exposed

causes sensitivity

Cementum is resistant to resorption especially in younger

Patients. Thus, orthodontic tooth movement causes alveolar

one resorption and not tooth root loss


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Alveolar Process

Gingiva


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Near the end of the 2ndmonth of fetal life, mandible

and maxilla form a groove

that is opened toward the

surface of the oral cavity

As tooth germs start to

develop, bony septa form

gradually. The alveolar

process starts developing

strictly during tooth eruption.


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a) outer cortical plates

b) a central spongiosa

c) bone lining the alveolus (bundle

bone)

Alveolar bone proper: The compact or dense bone that lines the tooth.


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Contains either perforating fibers from periodontal ligament (Sharpeys

fibers) or just compact bone

Sharpeys fibers embedded into the alveolar bone proper

Present at right angles or oblique to the surface of alveolar bone and

along the root surface

Because alveolar process is regularly penetrated by collagen fiber bundles,

it is also called bundle bone. It appears more radiodense than surroundingsupporting bone in X-rays called lamina dura


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Bundle Bone

It is perforated by many foramina that transmit nerves and vessels

(cribriform plate).

Radiographically, the bundle bone is the lamina dura. The lining of the

alveolus is fairly smooth in the young but rougher in the adults.

Radiodense because increased mineral content around fiber bundles

Lamina Dura

Supporting Compact Bone


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Supporting Compact Bone

Similar to compact bone anywhere else (Haversian bone)

Extends both on the lingual (palatal) and buccal side

Contains haversian and Volkmans canals (they both form a continuous

channel of nutrient canals)

Bundle bone and Trabecular bone


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Bundle bone and Trabecular bone

Arrows: Sharpeys fiber


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The alveolar crest is found 1.5-2.0 mm below the

level of the CEJ.

If you draw a line connecting the CE junctions of

adjacent teeth, this line should be parallel to thealveolar crest. If the line is not parallel, then there is

high probability of periodontal disease.

Cli i l id ti


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This process can occur during orthodontic

movement of teeth. Bone is resorbed on the side of

pressure and opposed on the site of tension.

Decreased bone (osteopenia) of alveolar process

is noted when there is inactivity of tooth that does

not have an antagonist

Clinical considerations

Resorption and regeneration of alveolar bone


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Lack of antagonists


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Periodontal Ligament

PDL is the soft specialized connective tissue situated betweencementum and alveolar bone proper

Ranges in thickness between 0.15 and 0.38 mm and is

thinnest in the middle portion of the root

The width decreases with age

Tissue with high turnover rate

Contains fibers, cells and intercellular substance

Embryogenesis


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Embryogenesis

The PDL forms from the dental follicle shortly after root

development begins

FUNCTIONS OF PERIODONTIUM


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Tooth support

Shock absorber: Withstanding the forces of mastication

Sensory receptor necessary for proper positioning of the

jaw

Nutritive: blood vessels provide the essential nutrients to

the vitality of the PDL

FUNCTIONS OF PERIODONTIUM


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Cells

a) Osteoblasts

b) Osteoclasts (critical for periodontal disease and tooth

movement)

c) Fibroblasts (Most abundant)d) Epithelial cells (remnants of Hertwigs epithelial root sheath-

epithelial cell rests of Malassez)

e) Macrophages (important defense cells)

f) Undifferentiated cells (perivascular location)

h) Cementoblasts

i) Cementoclasts (only in pathologic conditions)

Epithelial Cell Rests of Malassez


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Epithelial Cell Rests of Malassez


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PDL fibers

- Collagen fibers: I, III and XII. Groups of fibers that are

continually remodeled. (Principal fiber bundles of the PDL).

The average diameter of individual fibers are smaller than

other areas of the body, due to the shorter half-life of PDL

fibers (so they have less time for fibrillar assembly)

- Oxytalan fibers: variant of elastic fibers, perpendicular to

teeth, adjacent to capillaries

- Eluanin: variant of elastic fibers

Principal Fibers


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Dentoalveolar group

a. Alveolar crest group (ACG): below CE junction, downward, outward

b. Horizontal group: apical to ACG, right angle to the root surface

c. Oblique group: most numerous, oblique direction and attaches

coronally to bone

d. Apical group: around the apex, base

of sockete. Interradicular group: multirooted teeth

Runs from cementum and bone , forming

the crest of the interradicular septum

At each end, fibers embedded in boneand cementum: Sharpeys fiber

pRun between tooth and bone. Can be classified as dentoalveolar

and gingival group


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Gingival ligament fibers: the principal fibers in the gingival

f f


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area are referred to as gingival fibers. Not strictly related to

periodontium. Present in the lamina propria of the gingiva.a. Dentogingival: most numerous; cervical cementum to f/a gingiva

b. Alveologingival: bone of the alveolar crest to f/a gingivac. Circular: around neck of teeth, free gingiva

d. Dentoperiosteal: runs apically from the cementum over the outer cortical

plate to alv. process or vestibule (muscle) or floor of mouth

e. Transseptal: cementum between adjacent teeth, over the alveolar crest


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Transeptal

Alveolar crest

Horizontal

Oblique


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Oxytalan Fibers


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Type of elastic fibers present as bundes of microfibrils that run oblique

from the cementum surface to the blood vessels. Associated with neural

elements. Most numerous in the cervical area.

Function: Regulate vascular flow in relation to tooth function


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The PDL gets its blood supply from perforating

arteries (from the cribriform plate of the bundlebone).

The small capillaries derive from the superior &

inferior alveolar arteries.

The blood supply is rich because the PDL has a

very high turnover as a tissue.

The posterior supply is more prominent than the

anterior. The mandibular is more prominent than

the maxillary.


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Nerve supply

The nerve supply originates from the inferior

or the superior alveolar nerves.

The fibers enter from the apical region and

lateral socket walls.

The apical region contains more nerveendings (except Upper Incisors)


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Interstitial Space


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Interstitial Space

Present between each bundle of ligament fibers

Contains blood vessels and nerves

Designed to withstand the impact of masticatory forces

Ground Substance


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Amorphous background material that binds tissues and fluids

A major constituent of the PDL

Similar to most connective tissue ground substance

Dermatan sulfate is the major glycosaminoglycan

70% water; critical for withstanding forces

When function is increased PDL is increased in size and fiber thickens

Bone trabeculae also increase in number and thicker

However, in reduction of function, PDL narrows and fiber bundles

decreases in number and thickness (this reduction in PDL is primarily due

to increased cementum deposition)


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14 periodontium

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