4- The Periodontium (Mahmoud Bakr)

7/27/2019 4- The Periodontium (Mahmoud Bakr)

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Griffith UniversityOral Biology 2

1009 DOH

The Periodontium

Dr. Mahmoud Bakr

Lecturer in General Dental Practice

B.D.S, M.D.S (Cairo University), ADC (Australia)Member of the Australian Dental Association (ADA),

the Australian Biology Institute Inc. (ABI) and the

Egyptian Dental Union (EDU)


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Learning objectives:After completing this lecture you should be able to:

1- Name, classify, identify and describe the

structure and function of the components of

Cementum, PDL and Alveolar Bone.

2- Describe age related changes to Cementum, PDL

and Alveolar Bone and their effects.

3- By observing the histological details of cells and

tissues, you should be able to use a microscope toidentify different histological structures of

Enamel and understand the histological processes

involved in preparing slides.


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All Microscopic images are taken from the

Digital Library of the Oral Biology Department

(Cairo University).


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The Periodontium is the group of tissues

responsible for supporting the tooth.

In other words it is considered as theattachment apparatus of teeth.

It consists of:

Two hard tissues: Cementum

Alveolar Bone

Two soft tissues: PDL

Gingiva


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Acellular cementum (20-50 m)

Cellular cementum (150-200 m)

Physical Characteristics

2- Thickness

1-ColorLight yellow

Lighter in color than dentin

3- Permeability

Permeable from dentin and PDL sides.

Cellular C is more permeable than acellular C.


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Chemical Composition

45-50 % Inorganicsubstances

50-55% Organicsubstances

Hydroxyapatitecrystals

Collagen

protein

Polysaccharides

Trace elements

Cementum contains the greatest amount of

fluoride in all mineralized tissues


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Cementum Structure

Acellular cementum Cellular cementum

Cementoid

layer

MalassezCementocytes


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Acellular CementumThickness is 20-50 .

It is clear and contains no cells.

Covers the coronal half of the root.

Less permeable than Cellular

Cementum.

Incremental lines of Salter are parallel

to the surface and closer to each

other.

Sharpeys fibers space can be seen in

it .

Alternating layers of

Acellular and Cellular Cementum

could be seen.


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Cellular Cementum

Lacunae of cementocytes

PDL side

Dentin side


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Cellular Cementum

Lacunae of cementocytes

Cementocytes

PDL side

Dentin side

CementocytesIncrementallines of Salter


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Cementocyte And Osteocyte

Dentin side

PDL side

Lacuna

Canaliculi

Osteocyte


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Cementocyte And Osteocyte

Periodontal

ligament side

Dentin side

Lacuna

Canaliculi

Osteocyte


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Have you spotted the difference?

The processes of Cementocytes are longer onthe PDL side than on the Dentin side.

While the processes of Osteocytes are of equal

length from both sides.


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WHY???????


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Because the PDL side is where the superficial

layers of Cementum get their nutrition from

(so the processes are long), while the Dentin

side is a just a hard tissue (no nutrition).


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Cellular Cementum

Dentin side

PDL side

Viablesuperficial

cementocytes

Degenerated

deep layers

cementocytes


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Incremental Lines Of Salter

They are hypermineralized area with less

collagen fibers and more ground substance

In Acellular C In Cellular C


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Intermediate Cementum

Premature

degeneration of

epith. Root sheath

of Hertwig ( after

odontoblasts

differentiation andbefore dentin

formation)

It occur at apical 2/3 of premolars and molars

roots and rare in incisors and deciduous teeth

Contains

entrappedepithelial cells


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Afibrillar Cementum

The enamel at cervical

area not covered by

reduced dental

epithelium before

tooth eruption

The connective tissue of

the dental sac lay down

cementum on the

exposed enamel


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Types Of Cementum

1- Acellular cementum

2- Cellular cementum

3- Intermediate

cementum

4- Afibirllar cementum


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Cemento Dentinal Junction

CD

Smooth in permanent teeth Scalloped in deciduous teeth


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Cemento Enamel Junction

30% cementum

meets the enamel

in a sharp line

10% cementum and enameldoesnt meet because of

delayed separation of epith

root sheath of Hertwig (area

of dentin not covered by C).

60%

cementum

overlaps E

(afibrillar

cementum)


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Functions Of Cementum

1- Acts as a medium forattachment of collagen

fibers of PDL (Sharpeys

fibers).

2- The continuous formation

of cementum keeps theattachment apparatus

intact.

Cementoid T

Cementoblast


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3- Cementum deposition

epically compensate forthe attrition.

4- It is a major reparative

tissue

( as in case of fracture or

resorption of root)


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Cementogenesis

1-Matrix formation 2- Maturation

Collagen

fiber type I

Ground

substance

Hydroxy apatite

crystals


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1- Matrix formation

Cementum is formed

during root

formation

Future C E J Epith. Diaph.

H E R

D

Cementoblasts


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Cementoblast is a protein forming and secreting cell.

D

Cementoblast

Large open face nucleus

R E R

Golgi apparatus

Mitochondria

Alkaline phosphatase

Secretory granules

Collagen fibers +ground substance.

Cementum

Cementoid layer

C

ementoblasts

Maturation occur layer

by layer for the

collagen fibers


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Age Changes Of The Cementum

DD

Localised

1- Hypercementosis.

May affect one tooth or all teeth Hypercementosis


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Hypercementosishyperplasia

Hypercementosishypertrophy

Increase number of

Sharpeys fibers

Decrease number of

Sharpeys fibers

Types Of Hypercementosis


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Hypercementosis


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2- Permeability

Fromperiodontal

side, but remain

at the

superficial

recently formed

layers

From dentin

side

remains at

apical area

ONLY


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The periodontal ligament is the

dense fibrous connective tissue

that occupies the periodontalspace between the root of the

tooth and the alveolus.

Hi t l i l t t


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cells

Histological structure

The periodontal ligament is formed of:

Fibers,

Intercellular

substances

Synthetic

Resorptive

Progenitor

Defensive

ground substances

blood vessels,

nerves & lymphatics.


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epithelial cellsremnants of the epithelial

root sheath of Hertwig

The cellsSynthetic

cells

Resorptive

cells

Progenitor

cells

Defensive

cells

fibroblasts, osteoblasts cementoblasts.

cementoclasts , osteoclasts fibroclasts.

undifferentiated mesenchymal

cells

macrophage, lymphocytes

and mast cells


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II- The fibers

*The fibers of the periodontal ligament are

mainly collagen.

They are divided into:

A) The principal fibers.

B) The accessory fibers.

C) The oxytalan fibers.

*Elastic fibersare restricted almost entirely to

the walls of blood vessels.


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A- The principal fibers of periodontal ligament

are formed of collagen bundles, which are wavy

in course and are arranged in three ligaments .a) Gingival fibers.

b) Transeptal or Interdental ligament.

c) Alveodental ligament which is subdivided into thefollowing five groups:

1- Alveolar crest group.

2- Horizontal group.

3- Oblique group.

4-Apical group.

5- Inter-radicular group.


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1- The principal fibers:

a- The gingival fibers:

1- Gingiva fibers: extend from thecervical cementum into the laminapropria of the gingival.

2-Alveogingivalgroup: extends fromthe alveolar crest into the lamina

propria.3- Circular group: a small group of

fibers that encircles the tooth andinterlaces with the outer fibers .bone.

4- Dentoperiostealfibers: theyextend from the cementum directover the crest and then inclineapically between the periosteumof the alveolar bone to the lamina

propria of the gingiva.

Alveolo-

gingivalDento-

gingival

Dento-

periosteal

Circular

fibers


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Gingival fibers form a rigid cuff around

the tooth that can add stability.


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b- The Transeptal ligament:

*It connects two adjacent teeth.*The ligament runs from the

cementum of one tooth over

the crest of the alveolus to thecementum of the adjacent

tooth.

Dentin

Dentin

Bone


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c- The Alveolodental ligament:

1-Alveolar crest group:radiate from the crest of the

alveolar process and attach

themselves to the cervical

part of the cementum.

2-Horizontal group:

The fiber bundles run fromthe cementum to the bone

at right angle to the long

axis of the tooth.

Bone Dentin


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4- Apical group:

The bundles radiate from theapical region of the root to

the surrounding bone.

5- Inter-radicular group:The bundles radiate from the

inter-radicular septum to

the furcation of the multi-

rooted tooth.

dentin

bone

dentin

bone


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B- Accessory fibers:

It is collagenous in nature and run from bone tocementum in different planes, more

tangentially toprevent rotation of the tooth

and found in the region of the horizontalgroup.

l f b


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C- Oxytalan fibers

These are immature elastic(pre-

elastic) fibers.They need special stains to be

demonstrated.

They tend to run in an axial

direction, one end beingembedded in bone orcementum and the other inthe wall of blood vessels.

At the apicalregion they form a

complex network.


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The function of the oxytalan fibers has been

suggested that they play a part in supporting the

blood vessels of the periodontal ligament during

mastication i.e., it prevents the sudden closure of

the blood vessels under masticatory forces.


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Interstitial tissue

It is found between the fibers of

the periodontal ligament.

They are areas containing some

of the blood vessels,

lymphatics and nerves and

surrounded by loose

connective tissue.

l d l


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Blood supply

The arterial blood supply of the periodontal

ligament is derived from 3 sources:

3- Branches from the apicalvessels that supply the dental pulp.

2- Branches from the intra-alveolarvessels, these branches run

horizontally and these constitute the

main blood supply.

1- Branches from thegingivalvessels.

Nerve supply:


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Nerve supply:

The nerve supply of periodontal ligament comesfrom either the inferior or superior dental nerves.

1- Bundles of nerve fibers run from the apicalregionofthe root towards the gingival margin.

2- Nerves enter the ligament horizontally through

multiple foramina in the bone.

mechanoreceptors

large fibers

Small fibers pain sensation

touch & pressure

Functions of the periodontal


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Functions of the periodontal

ligament:1- Supportive:

*periodontal ligament permits the teeth towithstandthe considerable forces of mastication.

*As the force is applied on the teeth, the wavy

courseof the collagen fibers graduallystraightening out and then acting as inelasticstrings transmitting tension to the wall of thealveolus.

*Also periodontal fibers being non elasticpreventthe tooth from being moved too far.

D i ti ti th h


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During mastication or throughapplication of an orthodontic

force:

Partof the periodontal ligamentwill be narrowed andcompressed.

Other parts of the periodontalligament will be widened.

This provides support for the loadedtooth, where the collagen fibersand the ground substance act ascushion.

Blood vesselsand all the components of the ligament acttogether as a hydraulic damper or shock absorber with theground substance and the tissue fluid.


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2- Sensory:

The periodontal ligament having the mechanoreceptorcontributes to the sensation of touch and pressure

on the teeth.

sudden overload proprioceptive reflexinhibition of the activityof the masticatory muscles

Opening the mouth

3 N t iti


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3- Nutritive:

The blood vessels in the periodontal ligament provide

nutrient supply required by the cells of the ligamentand to the cementocytes and the most superficialosteocytes.

4- Formative:Thefibroblastsare responsible for the formation ofnew periodontal ligament fibers and dissolution ofthe old fibers

Cementoblasts and osteoblastsare essential in buildingup cementum and bone.

5 Protective


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5- Protective

The protective function of the periodontal ligament is achieved by:

a- The principal fibers.b- The blood vessels.

c- The nerves.

a- The principal fibers:

The arrangementof the fiber bundles in the different groups is welladapted to fulfill the functions of the periodontal ligament.

TheAlveodentalligament transforms the masticatory pressure exertedon the tooth into tension or traction on the cementum and bone.

If the exerted force on a tooth is transmitted as pressure this will lead

to differentiation of Osteoclasts in the pressure area and resorptionof bone.


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b- The blood vessels:

The capillaries form a rich network, they are arranged inform of a coiland attached to bone and cementumthrough the oxytalan fibers.

This arrangement makes it possible when pressure isexerted on the tooth, the blood does not escapeimmediatelyfrom the capillaries and thus buffering the

pressure action before it reaches the bone.The behavior of the blood in the capillaries may be

simulated to a hydraulic brake.

c- The nerves:By its mechanoreceptors nerves.


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The Age Changes of periodontal ligament

*The periodontal ligament through aging shows

Vascularity

Cellularity

Thickness

*It may contain cementicles.

The cementicles appear near the


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surface of cementum may befree , attached or embeddedin

the cementum.They have nidusfavoring the

deposition of concentric layersof calcosphrite as degenerated

cells, area of hemorrhage andepithelial rest's of Malassez.

Cementicles are usually seen in

periodontal ligament by agingbut in some cases they may beseen in a younger person afterlocal trauma.


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Clinical considerations

1 Knocked out tooth (Avulsion)


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1-Knocked out tooth (Avulsion)

A tooth that is replaced within half an hour has a 90% chance

of successful re-implantation.

The length of time before a tooth is re-implanted and how it is

transported to the dentist are crucial in successfully saving andre-implanting the tooth.

The periodontal ligament will regenerate and re-vascularize.


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Adequate periodontal therapyand maintenance

in patients with periodontal diseases

reduces tooth loss by 70%

2- Periodontal disease:


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Dental implants lack periodontal ligament fibersand they have a rigid connection to bone.

3- Dental Implants:


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Thats why Implants may fail under

excessive load as they cant withstandthe forces applied on them due to lack

of the flexibility of PDL.

Peri implant tissues


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Peri-implant tissues

Titanium implant

Sulcular epithelium

Junctional epithelium

Connective tissue

Bone


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B i i li d t f ti


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Boneis specialized type of connective

tissue with calcified intercellular

substance.

Functions:

1-Skeletal support of the body.

2-Store for calcium and phosphate which may be mobilized

according to needs of the body.

3-Protect for the internal organs.

4-Manufacturing for blood elements.


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Bone components:

1Cells

2Matrix components

Mineral content 65%

Organic extra-cellular matrix 35%Organic extra-cellular matrixis the collagen fiber

and the ground substance.

1 C ll l


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1- Cellular components:

Osteogenic cells.

That form and maintain bone.

Osteoclasts

That resorb bone.

a-Osteoprogenitor cells

b-Osteoblasts

c-Bone-lining cells

d-Osteocytes

Cellular components:


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Cellular components:

Osteoprogenitor

cells

a Osteoprogenitor cells:


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aOsteoprogenitor cells:

*They derived from

mesenchymal tissue

*They give rise toosteoblastsin well

vascularized regions

and tochondroblasts

in avascular region

a Osteoprogenitor cells:


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*The cells have pale

elongated nucleus and

sparse eosinophilic

cytoplasm.

*site:

1- In the deepest layer of

the periostium.

2- In the endosteum.

aOsteoprogenitor cells:

b Osteoblasts:


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b Osteoblasts:

*They are arising fromcondensing mesenchyme.

*They are cuboidal or slightlyelongated cells.

*Their cytoplasm is rich inprotein synthetic andsecretory

organelles.

Following maturation osteoblasts may


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Following maturation, osteoblasts may

*UndergoApoptosis,

*Become encased in matrix as osteocytes or

*Remain on the bone surface as bone-lining cells.

Osteoblasts:


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Osteoblasts:

MINERALIZED

BONEOSTEOID

TISSUE

By E\M osteoblasts containwell developed rough

endoplasmic reticulum (1),

extensive Golgi apparatus(2),

numerous mitochondria(3)

and secretory vesicles (4).

3

4

1

2

4

c-bone-lining cells:


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c bone lining cells:

*They are osteoblasts thatare no longer forming cells.

*They contain few synthetic

organelles.

*They contact with osteocytes

by Gap junctions.

*They are considered a

primary site for mineral ion

exchange between blood and

adult bone.

d-Osteocytes:


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d Osteocytes:

*They are surrounded by bonematrix, whether mineralized

or not.

*The cells present in a space

called osteocytic lacunae.

*Narrow extensions of theselacunae form canaliculi, that

house radiating osteocytic

processes.

Osteocytes: Cytoplasmic


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y

*Through these canaliculi

osteocytes maintain contact withadjacent osteocytes and with the

osteoblasts orlining cells on the

bone surface via gap junctions.

*Osteocytes have a decreased

quantity ofsynthetic andsecretory

organelles.

N

y p

process.

Osteocytes:


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Osteocytes are metabolically active cells:

1 - Maintain bone tissue and

2 - Play an important role in releasing calcium ions

from bone matrix when calcium demands increase.

Releasing calcium ions

occurred by Osteocytic

osteolysis which is local

degradation of bonesurrounding the cells, thus

influencing the structure of

the peri-lacunar matrix.

Osteoclasts:


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Osteoclast

Osteoclasts:

Origin of osteoclasts:

1-The fusion of circulating

blood-derived monocytes and

thus belong to themononuclear phagocyte

system or

2 - Differentiate from theosteoprogenitor cells in situ.

Osteoclasts:


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Howships

lacuna

They are located on the surface

of bone tissue where resorption

is taking place, in a bay like

depressions, calledHowshipsLacunae

Osteoclasts:

Osteoclasts:


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*Large multinucleated (2100nuclei) cells; however,

Mononucleated cells are also

present, with a foamy

eosinophilic cytoplasm.

Osteoclasts:

*The osteoclasts are variable in

shape due to their motility

*Rich in acid phosphatase

enzyme, which is important for

bone resorption.

Osteoclasts:


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1-Ruffled

Border

Osteoclasts:

1-Adjacent to the bone surface

the cells form finger like

structure termedruffled border.

2-At the periphery of thisbordera clear or sealing zoneis

found.

Theplasma membrane of this

zone is apposed to the bone

surface and the adjacent cytoplasm

is enriched in actin, vinculin and

talin.

2

2

Function of the clear zone:


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*Attaches the cells to the mineralized surface.

*Isolates an acidic micro-environment between them &thebone surface.

3-The basal portion of theosteoclasts contain nuclei, Golgi

complex, mitochondria, RER and

vesicular structures.

3

An electron dense matrix layer is

often observed between the sealingzone and calcified tissue surface

known as lamina limitans.

BONE RESORPTION


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Howships

lacuna

BONE RESORPTION

1-Attachment of osteoclaststo the bone. One of the

mechanisms of attachment is

the concentration oflamina

limitans.

2-Demineralization:through

hydrogen pump from ruffled

border thus exposed theorganic matrix.

3-Degradation of exposed organic matrix by the action of

d h h d h


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osteoclast

enzymes asacid phosphataseandcathepsin B.

4- Endocytosis:at the ruffled

border to the degradation

products (organic and

inorganic).

5- Transportof soluble

products to extra cellular

fluid or the blood vascularsystem.

TYPES OF BONE


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TYPES OF BONE

1Lamellar bone.

2Non lamellated bone.

3Bundle bone.


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LAMELLAR BONE

LAMELLAR BONE (site)


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LAMELLAR BONE (site)

Skeleton and flat bones.


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LAMELLAR BONE

A

ACOMPACT BONE.

BCANCELLOUS (SPONGY)

BONE.


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A COMPACT BONE

SITES


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External covering of ribs,

vertebrae, flat bones of

the skull.

SHAFT OF LONG BONES

Histology


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Histology

Three patterns of lamellar organization in the shaft oflong bone:

3Interstitial lamellae.

1Circumferential or basic lamellae.

2Haversian lamellae.

1 Ci f ti l b i l ll


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1Circumferential or basic lamellae.

Exist immediately under the

periosteum, outer circumferential

lamellae (OCL).

And surrounding the medullary

cavity, inner circumferential lamellae

(ICL).

The ICL are of similar arrangement of OCL but with fewer

lamellae.

2 Haversian lamellae:


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GROUND SECTIONDECALCIFIED SECTION

3-Interstitial lamellae

Haversian lamellae

H. canal

2-Haversian lamellae:

Volkmanns canals


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B -SPONGYBONE

SITES


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SITES

EPIPHYSIAL

PLATE

SPONGY

BONE

Exist in the epiphysis of long bones, bony of the vertebrae,

ribs and central part of the flat bone.

HISTOLOGY


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HISTOLOGY

Inter connected network of bone

trabeculae with intervening bone

marrow spaces (MS).MS

MS

This bone trabeculae surrounded

by osteoblasts (OB) and consists

of bone lamellae containing

osteocytes

OB

Incremental lines of bone


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Incremental lines of bone

Three types of lines mark the successive layers of

bone:

Resting lines

Reversal lines (Rev)

Faint line

Resting

lines

1 Resting lines


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1- Resting lines

Indicates the rhythmic manner of boneformation with periods of rest alternating with

periods of activity.

Appears blue in H & E stained sections

2 Revresal lines


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2- Revresal lines

They indicate a past Osteoclastic activity.

They are scalloped lines corresponding to

adjacent Howships Lacunae.

The convex side is always towards old

resorbed bone.

They appear also blue in H & E stained

sections.

3 Faint line


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3- Faint line

It appears only in sections stained with Silver(Ag).

It is a black line that appears due to the 45

degree angulation between different layers of

collagen fibers preventing passage of silver

particles.

PERIOSTEUM


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PERIOSTEUM

Its specialized dense connective

tissue.

It consists of two layers:

Outer layer is fibrous (Fi).

Inner layer is osteogenic (Og).

Og

ENDOSTEUM


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ENDOSTEUM

Medullarycavity

Its a thin fibrocellular layer of connective tissue lines the

medullary surface of bones. The endosteal surface is less

active in bone formation than the periosteal one.

Medullarycavity


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SITE


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Foundin areas where bone is laid for the first time in a

new situation:

-Bone of the fetus =Embryonic bone.

-Callus of fracture =Bone of emergency.

-Healing sockets after tooth extraction.

The non lamellated bone is more radiolucent than lamellar

bone


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bone.

Note: The bone of emergencynever change directly into lamellar

bone but it must be resorbed and then replaced by lamellar bone.


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3 BUNDLE BONE

SITES Adjacent to theAdjacent to the PDL


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periosteum

medulla

bundle

bone

Bundle

bone

periosteum

BUNDLE BONE


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BUNDLE BONE

The term BUNDLE BONE was chosen because the

bundles of the principal fibers, of either the periosteum or

the periodontal ligament, continue into the bone as

sharpeys fibers

(extrinsic collagen

fiber bundles). PDL

Radiographically:


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It appears more radiopaque than does lamellated bone.

This increase in radiopacity is due to the presence of thick

bone without trabeculations and not to any increased

mineral content.


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Alveolar processis that bone of the jaws containing the sockets

of the teeth


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of the teeth.

*Its presence depends on the presence of teeth.

*The remaining bony part of the mandible or maxilla is called

thebasal bone.

Alveolar

process

Basal bone

*No line of

demarcation.

*Both arecovered by the

same periosteum.

The alveolar process hasfacialandlingual surfaces. There are

ridges corresponding to the roots of the teeth that invest in it


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ridgescorresponding to the roots of the teeth that invest in it.

Facialandlingualsurfaces are separated byalveolar septa.

These septa include: a- interdental septa.

B- inter-radicular septa.

Lingual surface.

Facial surface.

Ridges.

Alveolar process consists of:


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Alveolar process consists of:

*1- Facial and lingualcortical plates.

*2-Central spongiosa.

*3- Alveolar bone


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Alveolar boneandcortical plates

merge at thealveolar process crest.

1.5 to 2 mm below the cemento-enamel

junction.

CEJ

1- The cortical plates:Anatomically:


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y

Anterior teeth

L

L

Lb

Lb

Lingualplate is

thicker than labially.

Lower posterior

LB

L

B

Buccalplate is thicker

&denser than lingually.

Upper posterior

Lingualplate is

thicker than

buccally.

Histologically:C PDL

Alveolar Cortical


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g yC PDL

bone plate

The cortical plate consistsof

*layers of circumferential

lamellae.

*Supported by Haversian

system of variable

thickness.

2- The central spongiosa (Trabecular bone):


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Anatomically:

*It form the main bulk of the alveolar septa.

*In some cases the spongiosa is minimal or even absent.

*Trabecular bone is only present

in the apical third.

X-ray classification of the spongiosa:


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Type I:present in the lower inter-

dental and inter-radicular septa.

The bone trabeculae arranged

horizontally in the form of ladder.

Type II:common in the maxilla.

The bone trabeculae are irregularly

arranged.

Below the root apices, the trabeculae

radiating from the socket fundus in a

distal direction

Histologically:

The spongiosa is formed of interconnected network of bony


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Note:bone marrow spaces are smaller compared with those

present in the basal bone.

The spongiosa is formed of interconnected network of bony

plates enclosing bone marrow and surrounded by osteoblasts.

Large trabeculae show Haversian system

arrangement.

3- The alveolar bone proper:


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Anatomically:

Its perforated by channels through

which blood vessels &nerve fibers

connect the marrow spaces to the

PDL.

PDLAlveolarbone

So its calledcribriform plate.

Radiographically: its referred aslamina dura.


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Only excellent students would know that the name ofthose channels is

Zuckerkandle and Heirshefield canals

Histologically:


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Alveolar bone is formed of two types of bone,bundle bone

andlamellar bone.

In some cases, alveolar bone

can be made up almost

completely ofbundle bone.

The alveolar bone reveals double

fibrillar orientation

Extrinsic fibers (Sharpeys fibers)Intrinsic fibers

Clinical considerations:


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During extraction the thickness of thecortical plates determines the direction ofinitial movement (always towards thethinner side).

As a rule all teeth are extracted with a labialor buccal movement except lower Molars asthe buccal cortical plate is thickened by the

External Oblique Ridge so the initialmovement is towards the thinner lingualplate.

Are you an excellent student?


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y

What was the name of the canals

connecting the bone marrow spacesto the PDL?


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Documents

4- The Periodontium (Mahmoud Bakr)