Handout of Alveolar bone Histology

Histology of Alveolar Bone

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1
ST
Edition



















New Insight Into
Oral Histology
MO'men Gamal AboDaif

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Alveolar Bone
Introduction
Bone: Specialized mineralized vascular connective tissue
Function:
1. Protects the vital organs
2. Forms the body skeleton
3. Acts as a reservoir for calcium
Classification:
1-Bundle bone
2-Lamellated (mature) bone; a- Compact bone (Dense)
b- Spongy bone (Cancellous)
3-Non lamellar bone (woven, embryonic, immature)
NB:
•The woven bone is characterized by
1- Osteocytes large number, large size & irregular arrangement
2- Collagen Fibers Irregular arrangement
3- High organic contents & Small inorganic contents
•The woven bone is located in ••Embryonic bone
••Site of fracture healing

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The Alveolar Bone (Process)
Definition: Bone of Maxilla & Mandible that makes up the teeth sockets (Socket = Alveolus)
Origin: Dental Sac mesodermal cells
Functions: 1. Anchors the teeth with the help of Sharpey’s fibers
2. Protects the developing tooth Crypt of primary & permanent teeth until
their eruption
3. Absorb & distribute the occlusal forces
4. Helps in the movement of teeth for proper occlusion
Chemical composition

Inorganic matrix Organic matrix
67% 33%
Calcium & Phosphate ions in the form of
Hydroxylapatite crystals

Chemical formula: Ca10(PO4)6(OH)2
28% Type I collagen
5% Noncollagenous proteins including:
••Osteo-nectin
••Osteo-calcin
••Bone Morphogenic protein
••Bone Sialo-protein
••Bone Proteo-glycans
••Ratio between hard & soft components is sufficient (to ensure a Degree of elasticity)
NB: The alveolar bone controlled by:
• Hormonal factor (Systematically)
• Mechanical forces, including tooth movements (Locally)
Development
•At the end of 2
nd
month i.u, Maxilla & Mandible form a groove (Open toward oral cavity surfaces)
••This groove contains: Tooth germs, alveolar nerves & vessel
•Gradually Bone Septa develop between adjacent tooth germs
•Mandibular canal is separated from the dental crypts by a Horizontal plate of bone
NB: ••Time: Only during the teeth eruption
••Type of Ossification: intra-membranous
••After teeth loss, it gradually diminishes in height

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Macroanatomy of Alveolar Bone composed of
1- Alveolar bone proper (consists of Bundle & Lamellated bone)
2- Supporting alveolar bone (consists of Compact & Spongy lamellar bone)

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Microanatomy of Alveolar Bone
Bundle bone (Discuss)
Definition: Part of the alveolar bone where PDL principal fibers are attached
Site: Surrounds the roots of the teeth
Function: Gives attachment to the PDL principle fibers to support the teeth anchoragement
NB: Principal fibers bundles continue into the bundle bone as Sharpey’s fibers
So, it’s termed as Bundle Bone (Histologically)
Structure:
Consists of thin lamellae of bone which
-Has Zucker Kandle or Hirschfeld
canals: numerous small openings in this
bone plate, allowing blood vessels & nerves
(in Bone & PDL) to communicates freely or
anastomose
So, it’s termed as Cribriform Plate
(Anatomically)
NB: •It’s termed as Lamina Dura
(Radiographically)
Because it appears as a light line (Radiopaque)
on radiographs
Not because it contains high mineral content
than the surrounding bone
But because it’s dense, thick bone without trabeculation

Lamellated bone
Site: lies adjacent to the bundles bone layer
Structure:
Formed from
-Lamellae which are arranged parallel to the surface of the adjacent Endosteum OR Haversian system

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Compact Bone (Discuss)
Site: Surrounds the alveolar bone proper buccally & lingually
Function: Gives support to the tooth socket
Structure: • Macroanatomy (Anatomy); It consists of
••Outer Cortical Plate covers buccal surface of mandible &
maxilla
••Inner Cortical Plate covers lingual surface of mandible &
maxilla
NB: Generally, the compact bone is much thicker
-in Mandible than Maxilla
-in Posterior region than Anterior
-It’s thickest in The Mandibular Posterior region, especially on the buccal side
-It’s thinnest in The Maxillary Anterior region

• Microanatomy (Histology); Similar to any Haversian Bone
Unit Structure: Osteon
It’s formed of: Lamellae, Canal System & Cells
NB: It’s covered externally by Periosteum & lined internally by Endosteum
a. Bone Lamellae
Outer Circum-ferential
Lamellae
Inner Circum-ferential
Lamellae
Concentric Lamellae Interstitial
Lamellae
Shape Longitudinal lamellae Longitudinal lamellae 4-20 Round lamellae Interrupted lamellae
Site Parallel with Periosteum Parallel with Endosteum Surrounding haversian
canals
Between Concentric
lamellae
Contain Calcified C.T &
Osteocytes
Calcified C.T &
Osteocytes
Osteocytes in their lacuna
which connected to each
other by Canaliculi
NB: it’s thought to
be the old resorbed
remnant of bone
b. Canal (Haversian) System; provides a Nutrient Network throughout bone
Haversian Canal Volkman’s Canal Transverse Canal
Dir
. Parallel to the long axis of the
bone
Enter Haversian canals at Right
Angle
Enter Haversian canals at Right
Angle
Function
Contains Nerves & B.Vs
Surrounded by the concentric
lamellae
Connect Haversian Canal with
a. Periosteum
b. Endosteum (Bone Marrow
Spaces)
Connect between two haversian
canals

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Spongy bone (Discuss)
Unit Structure: Bone Trabeculae
Site: Between cribriform & cortical plates (lamellar bone)
Function: Support alveolar bone proper of the alveolar
process
Structure: Composed of Trabeculae & Bone Marrow Spaces between them
•Trabeculae are made up of ••adjoining lamellae (varying number)
••lacunae of osteocytes in between
•Bone Marrow contains ••Blood forming elements
••Osteogenic cells
••Adipose tissue
Types
Type I Type II
Arrangement
of trabeculae
(inter-dental &
inter-radicular)
Regular & Horizontal
“Ladder like arrangement”
Irregular with numerous fine delicate
Site Common in Mandible
NB: From apical part of lower molars socket,
bone trabeculae are radiating in slightly
Distal direction
Common in Maxilla

Clinical
Considerations

Nerve Block Anesthesia
Local Infiltration Anesthesia
NB: Spongy bone is
•Very dense around the teeth, which are subjected to excessive mastication forces
•Shows very wide medullary spaces & few numbers of trabeculae around functionless teeth

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Cells Osteoblast Osteocyte Osteoclast
Site



With their axis is perpendicular to
the surface with which they aligned
•Between Concentric
Lamellae
•Between Circum-ferential
Lamellae
Cluster rather than singly
•against bone surfaces where
the resorption is taking place
•in Howship lacunae, which the
cells themselves have created
Origin

Mesenchymal in origin from
•UMC (stem cells)
•Preosteoblasts
•Imprisoned osteoblasts
as they secret bone matrix,
some of them entrapped in
lacunae
•Circulating blood monocytes
•Osteoprogenitor cells in situ.
(Local Osteoblasts)
Function

•Synthesize both collagenous &
non-collagenous bone protein
•Maintain bone Vitality •Bone resorbing cells
•Osteoblast-osteocyte complex: Prevent hypermineralization of
bone by continually pumping calcium back into blood stream
Shape

L.M

Cell Body

•Active: Plump cuboidal cells
with a few cytoplasmic process
•Inactive: Flat, more squamous
cells (Lining cells)
Flat branched cells
surrounded by bone matrix
•Surrounded by a Space of
lacuna from which canaliculi
arise
•Canaliculi
••Contain the cell process
••Connecting neighboring
osteocytes together
Irregular, oval or club shaped
with many branching processes
•Ruffed Borders: the wavy &
undulated portion adjacent to
the bone surface
-is surrounded by a Clear zone
that has only Fine granular
cytoplasm with microfilaments
Nucleus

•Uninucleated cell
-Active: open-faced
-Inactive: closed-faced
(Lining cells)
•Uninucleated cell •Multinucleated cells
(dozen or more)
Not due to division of the
nucleus
But due to fusion of a number of
individual cells
•However, uninucleated
osteoclasts are found
NB: Nuclei number & cells size
depends on Resorbed Bone Type
Cyto.

•Basophilic, rich in alkaline
phosphatase enzyme
•Basophilic •Acidophilic, rich in Acid
Phosphatase Enzyme
(in Vacuoles & Vesicles)
E.M

Organelles
Protein Secreting Cells
1-Well-developed RER
2-Golgi apparatus
3-Secretory vesicles
4-Ribosomes
1-Well-developed RER
2-Golgi apparatus
3-Secretory vesicles
4-Ribosomes
Lesser in Size & Number than
that of the Osteoblast
Resorbing Cells
1-Foamy granules
2-Prominent mitochondria
3-Lysosomes
4-Vacuoles
5-Little RER

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NB:
*Osteoprogenitor cells
Defi: Undifferentiated cells have high capacity to differentiate to other bone cells
Site: •lining the bone vascular canal
•Deepest layer of periosteum & endosteum
•Osteoblast-osteocyte complex: Each osteocyte maintains contact with adjacent osteocytes & osteoblast on
the bone surface (endosteum, periosteum & haversian canals)
••Most important function of the complex is to Prevent Hypermineralization of bone by continually
Pumping calcium back into the blood stream
•Number of osteoblasts that become osteocytes varies depending on Bone Formation Rapidity
“The more rapid the formation, the more osteocytes are present per unit volume”
•All bone cells are easily recognized in Light Microscope

Bone resorption; It takes place in 3 processes:

Decalcification


Decalcification of Inorganic matrix
By secretion of organic acids mainly citric & lactic acids
that 1. Chelate bone
2. Increase solubility of hydroxyapatite (Inorganic)
This achieved at the Ruffled border of the osteoclasts

Degradation

Degradation of Organic matrix
By Lysosomal acid protease & Collagenase enzymes
That breaks down extracellular collagen fibers (Organic)

Then Only Calcium Phosphates can be identified inside the
osteoclasts

Transport


Transport of soluble products to
•Extracellular fluid
•Blood vascular system
By a mechanism not yet known