PERIODONTIUM

Oral mic anatomy and embyrology

BEE

PERIODONTIUM

Cementum

PDL

Alveolar bone

Sharpey's fibers

Attachment

organ

Cementum

Periodontal

ligament

Alveolar bone

Apical foramen

Pulp cavity Enamel

Dentin

Gingiva

Root canal

Alveolar vessels

& nerves

TEETH IN-SITU

Periodontium

Four tissue supporting the tooth in the jaw ◦ Cementum

◦ Periodontal ligament

◦ Alveolar bone

◦ Gingivae

Cementum

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 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

Cementum

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

inter-radicular regions

◦ Thin cervically (10-15 µm)

Contiguous with PDL Firmly adherent with root

dentine Highly responsive mineralized

tissue ◦ Maintenance of root integrity

◦ Maintenance of functional position of tooth

◦ Tooth repair & regeneration

Varies in thickness: thickest in the apex and

In 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

Cementum

Slowly-formed throughout life Allowing continual reattachment of PDL

fibers Cementum can be regarded as a

mineralized component of PDL Precementum - a thin mineralized layer

on the surface of the cellular cementum Similar to bone, however -

◦ Avascular & not innervated ◦ Less rapidly resorbed – orthodontics

Cement-enamel junction

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 properties

Pale yellow Softer than dentine Permeability

◦ 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 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

&/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 root

adjacent to dentin whereas cellular

cementum 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

A: Acellular cementum

B: Hyaline layer of Hopwell-Smith

C: Granular layer of Tomes

D: Root dentin

Cellular: Has cells

Acellular: 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 cementum

Cellular cementum

Hyaline layer

(of Hopewell Smith)

Granular layer of tomes

Dentin with tubules

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

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 cellular

cementum. 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

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

Acellular cementum

Most common pattern- adjacent to dentine

Structureless Afibrillar cementum

◦ Exists between Acellular cementum

Hyaline layer (of Hopewell-Smith)

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

Acellular cementum •Root dentine

•Fibres of

Periodontal

Ligament

•Cementum •Epithelial

Rests

Cellular 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 cementum

Cementum 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 but

phasic, deposition of cementum)

Clinical Correlation

Cementum is more resistant to resorption: Important in permitting

orthodontic tooth movement

Cementocytes vs. osteocytes

Cementocytes ◦ More widely dispersed

◦ Randomly arranged

◦ Canaliculi oriented towards PDL – nutrition

Osteocytes ◦ Osteon – Haversian system

◦ Organized cells

◦ Circumferential lamellae

Relationship between acellular & 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 cementum

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

Intrinsic fiber cementum ◦ Run parallel to root surface at right angles to extrinsic fibers

◦ Fibers derived from cementoblasts

Acellular extrinsic fiber cementum

AEFC Over cervical half – 2/3s of the root Bulk of cementum in premolars First formed cementum - acellular Thickness of 15 µm All collagen are from Sharpy’s fibers Though GS from cementoblasts Fibers well-mineralized

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 be

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

Acellular intrinsic fiber cemetum

If cementum forms slowly in CIFC

Cellular mixed stratified cementum

Alternating AEFC with CIFC

Root apex

Furcation areas

Mixed-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 lines

Irregular rhythm of deposition Not related to activity & quiescence Related to

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

Imprecise periodicity Acellular – closer, thinner & regular lines Cellular - farther apart, thicker & irregular

lines

Development of Cementum

Cementum formation occurs along the

entire tooth

Hertwig’s 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

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?

Cementoblasts

Derive from dental follicle

Transformation of epithelial cells

Incremental lines

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

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

Reparative cementum vs. cementum

Wider uncalcified zone

Less mineralized

Smaller crystals

Calcific globules are present

Differences are related to different speed of formation

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

Clinical considerations

Supra-eruption of teeth Tooth wear Local hypercementosis

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

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

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 the alveolar crest

◦ The dental pulp at the apical foramen

Periodontal ligament space

Variable in width, average 0.2 mm

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

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

Components of PDL

Fibers

Ground substance

Cells

Fibers 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 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 PDL

Sharpy’s fibers

Principal fibers embedded into cementum and bone

More numerous but smaller at cemental end

Mineralized and unmineralized parts

Ground substance of PDL

60% of PDL by volume Main 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 PDL Fibroblasts

◦ Fusiform cells with many processes

◦ Functions – secretion and turnover of fibers Regeneration of tooth

support apparatus Adaptive responses to

mechanical loading

Cementoblasts ◦ Cement-forming cells lining cemental surface

◦ Cuboidal cells Osteoblasts

◦ Bone-forming cells lining tooth socket

◦ Resemble cementoblasts

Cells 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 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 to alveolar bone

Capillary plexus around the tooth

Crevicular plexus of capillary loops

Veins do not follow arteries but drain into intraalveolar venous networks

Innervation of PDL

Sensory ◦ Nociception

◦ Mechanoreception

Sensitivity to occlusal loads

Guidance to intercuspation

Autonomic ◦ Associated with blood vessels

Alveolar process

The alveolar process develops during the eruption of teeth

Grows at a rapid rate at the free border

Proliferates at the alveolar crest

No 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 crypt

Deciduous tooth & permanent successor initially share crypt

Bone subsequently forms to encase permanent tooth