4- the periodontium (mahmoud bakr)
TRANSCRIPT
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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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