عملي Oral

انسجة فم عملي / د . اسماء ثاني اسنان موصل 21 / 12 / 2015 *

Dentin forms the main bulk of the tooth☻In crown it is covered by enamel☻In root it is covered by cementum *

Physical Characteristics

Yellowish in color. Elastic. Hard ( less than enamel but more than cementum and bone). By X-ray : more radiolucent than enamel and more radio-opaque than cementum. Thickness varies from 3-10 mm.
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Collagen type I

inclusions of insoluble proteins
glycoproteins and lipids
Hydroxyapatite crystals
70-75% inorganic material
30-25% organic material
Chemical Characters Of Dentin
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How To Study The Histological Structures Of Dentin

Ground section (inorganic part)
Decalcified section (Organic part)
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Types Of Dentin
Mantle dentin
Circum-pulpal dentin
Primary dentin
Sec. Ir D
Sec. RD
Dentin
Predentin
Odontoblasts
Secondary dentin
Predentin
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Histological Structure Of Dentin

Odontoblasts
Predentin
Dentin
Dentinal tubules
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Odontoblasts And Dentinal Tubules
D E J
Odontoblastic process
Preodontoblastic space
Peritubular dentin
Intertubular dentin
Odontoblasts
Mantle D
Circumpulpal D
Predentin
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Ground Section Of D. Ts.

At the cusp tip or (incisal edge)
At cervical area
Mid portion of root and apically
Straight
S shape
Straight
Secondary curvatures
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Dentinal Tubules

Odontoblasts
Predentin
Dentin
Sec. curvatures
Terminal branches
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T.S. In Dentinal Tubules

Ground section
Neumann’s sheath Odontoblastic process (Tomes’ fiber) Periodontoblastic space
Scanning microscope
Decalcified section
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Incremental Lines Of Dentin

Incremental lines of von Ebner
Neonatal line
Contour line of Owen
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Interglobular Dentin
Calcification of dentin in some areas occurs in a form of globular pattern. These globules fuses together to form homogenous substance. Sometimes globules in some areas failed to fuse. Area of organic matrix between the globules remain uncalcified or partially mineralized. These areas bonded by the curved outlines of the adjacent globules.
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Tomes’ Granular Layer Tomes’ granular layer Cementum

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Interglobular dentin (Size) Large (Cause) Areas of unmineralized or hypomineralized dentin (sometimes present). (Site) Appear in the crown just below mantle dentin. (D T) Dentinal tubules cross the IGD without the peritubular dentin (IL) Follow incremental line pattern In badly formed tooth it appear in the root dentin
Tomes’ granular layer(Size) Small granular in appearance(Cause) Areas of minute IGD, but recent studies indicate that it result from the looping of the terminal portions of DT which is a result different orientation of odontoblastic process (always present) .(Site) Appear in the root adjacent to the cementum.(DT) Dentinal tubules do not cross this layer(IL) Does not follow any incremental pattern. *

Innervations Of Dentin

Plexus of Raschkow (suodontoblastic layer)
The nerve will loose its schwann caoting then pass between the odontoblasts bodies and enter the dentinal tubules ( In crown and fewer in the root )
High at D E J
High near the pulpal surface
Less sensitive area
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Theories Of Pain Transmission Through Dentin.

Direct neural stimulation
Odontoblastic transduction theory
Fluid or hydrodynamic theory
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Dentin Development
Odontoblasts differentiation
Early dentin formation
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Life Cycle Of Odontoblasts

1- Differentiation of odontoblasts.
Differentiate from the peripheral dental papilla cells (UMC)
At first become short columnar cell with many stubby processes
I D E
Basement membrane
The cells grow in length (40u) and closely packed together
Ameloblasts
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2- Formation of the predentin

Odontoblast become a protein forming and secreting cell. R E R , Mitochondria and Golgi bodies Ribonucleic acid and alkaline phosphatase
Inner dental epith side
Large open faced N
R E R
Mitochondria
Golgi bodies
Predentin
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3- Odontoblastic process formation
At first more than one process
As more D is laid down, the cells receed and leave single process ( Tomes’ fiber) *

The odontoblasts decrease in size and form dentin in a slowly diminishing rate until stimulated to form reparative dentin.
4- Quiescent state of odontoblasts
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Dentinogenesis

1 Matrix formation (Predentin) Collagen Ground fibers substance
2 Maturation (mineralization) Hydroxyapatite crystals
Dental papilla
Dental organ
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1- Matrix formation

A- Mantle dentin The first formed dentin layer in crown And root
Fibers are perpendicular to D E J
Fibers are parallel to basement membrane
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B) Circumpulpal dentin
Mantle dentin
Circumpulpal dentin. The fibers are parallel to DEJ ( right or oblique angle to DT)
Crowding of the cells and appearance of junctional complex
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Mantle dentin Thickness: 10-20 um Diameter of collagen fibers: large (0.1-0.2 um) Direction of collagen fibers : have right angle to DEJ and parallel to basement membrane in root Ground substance: from odontoblasts and the cell free zone Mineralization: linear form (contains matrix vesicles).

Circumpulpal dentin Thickness: bulk of the tooth Diameter of collagen fibers: small (0.05um) Direction of collagen fibers : have right or oblique angle to dentinal tubules (parallel to dentin surface) Ground substance: from odontoblasts Mineralization: Globular below mantle dentin then become mixed in the remaining circumpulpal dentin (no M V ).
Crown
Root
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2- Mineralization

Budding of matrix vesicles
Rupture of matrix vesicles
Mineralization of the mantle dentin
Has membrane rich in alkaline phosphatase
Calcium and phosphate ions undergo crystallization
Matrix vesicle
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Pattern Of Mineralization
M V in matrix
Crystallization
Lodgment of crystals
Rupture
1- Linear at the mantle dentin area
2- Globular in circumpulpal dentin just below mantle dentin
3- Combination in the remaining circumpulpal dentin of the crown and root
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Age Changes Of Dentin

Regular secondary dentin (Mild stimulus) Occurs on the entire pulpal surface. In multirooted teeth it is thicker on the roof and floor of pulp chamber. The size of the pulp cavity decrease and obliteration of the pulp horns The dentinal tubules change their direction to a more wavy course The no of dentinal tubules are fewer Line of demarcation (dark).
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Irregular Secondary Dentin (Reparative or tertiary dentin)

Severe stimulus The dentin is formed at a localized area. The dentinal tubules are less in number and irregular in arrangement. UMC from the subodontoblastic layer will differentiate and replace the degenerated odontoblasts to form reparative dentin
Irregular D T
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Types Of Reparative Dentin

Atubular dentin ( area without dentinal tubules)
Osteodentin (entrapped cells).
Vasodentin (entrapped b.v.)
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Secondary Dentin
Regular Cause: Mild stimuli (slow attrition and slowly progressing caries) Site of formation: Occurs on the entire pulpal surface of the tooth ( thicker on the roof and floor of the pulp chamber in multirooted teeth). Dentinal tubules: Change their direction and have more wavy course They decrease in number per unit area. Line of demarcation Present and stained dark.
Irregular Severe stimulus (abrasion, erosion, severe attrition and deep caries) Formed at the area corresponding to the pulpal end of the exposed dentin. Have irregular or twisted course They decrease in number and some areas may have no tubules (a tubular dentin). May or may not present
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Clinically: The decrease of the pulp chamber height and obliteration of the pulp horns make the liability of pulp exposure during cavity preparation much less likely to occur
The localized area of dentin formation increase the time taken by caries to reach the pulp (barrier)
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Transparent (Sclerotic Dentin)

Mild stimulus leads to changes for the dentin already present.
1- Odontoblast and its process undergo fatty degeneration.
2- Then there will be calcification of dentinal tubules. First become narrow by widening of the peritubular dentin.
3- Then the DT become obliterated.
The affected area have occluded dentinal, so the dentin have uniform refractive index. So this area of dentin appear translucent by transmitted light.
Transparent D
Trasparent D
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Dead Tracts
Severe stimulation to dentin leads to destruction of the odontoblastic process and odontoblasts. This leads to embty and wide dentinal tubules. These areas apear black with transmitted light. Under the dead tracts from the pulpal surface , reparative dentine will be formed. The dead tract serounded by sclerotic dentin.
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