Dentin

Dentin

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.

Collagen type I

inclusions of insoluble proteins
glycoproteins and lipids
Hydroxyapatite crystals
70-75% inorganic material
30-25% organic material
Chemical Characters Of Dentin


How To Study The Histological Structures Of Dentin
Ground section (inorganic part)

Decalcified section (Organic part)

Types Of Dentin

Mantle dentin

Circum-pulpal dentin

Primary dentin

Dentin
Predentin
Odontoblasts

Secondary dentin

Predentin

Histological Structure Of Dentin

Odontoblasts

Predentin
Dentin

Dentinal tubules

Odontoblasts And Dentinal Tubules

D E J

Odontoblastic process
Preodontoblastic space
Peritubular dentin
Intertubular dentin
Odontoblasts
Mantle D

Circumpulpal D

Predentin

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

Dentinal Tubules

Odontoblasts

Predentin
Dentin

Sec. curvatures

Terminal branches

T.S. In Dentinal Tubules

Ground section

Neumann’s sheath


Odontoblastic process (Tomes’ fiber)

Periodontoblastic space

Scanning microscope
Decalcified section

Incremental Lines Of Dentin

Incremental lines of von Ebner

Contour line of Owen

Interglobular Dentin

Calcification of dentin in some areas occurs in a form of globular pattern.
These globules fuses together to form homogenous substance.

Tomes’ Granular Layer

Tomes’ granular layer

Cementum

Interglobular dentin

(Size) Large
(Cause) Areas of unmineralized or hypomineralized dentin (sometimes present).
(Site) Appear in the crown just below mantle dentin.
(IL) Follow incremental line pattern
In badly formed tooth it appears in the root dentin
Tomes’ granular layer
(Size) Small granular in appearance
(Cause) it results 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.
(IL) Does not follow any incremental pattern.

Innervations Of Dentin

Plexus of Raschkow (suodontoblastic layer)

The nerve will loose its Schwann coating then pass between the odontoblasts bodies and enter the dentinal tubules ( In crown and fewer in the root )

Innervations Of Dentin

High at D E J

High near the pulpal surface
Less sensitive area

Theories Of Pain Transmission Through Dentin.

Direct neural stimulation

Odontoblastic transduction theory
Fluid or hydrodynamic theory


Dentin Development

Odontoblasts differentiation

Early dentin formation

Life Cycle Of Odontoblasts

1- Differentiation of odontoblasts.

Differentiate from the peripheral dental papilla cells

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

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

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 (decreasing) rate until stimulated to form reparative dentin.

4- Quiescent (not active) state of odontoblasts

Dentinogenesis
1 Matrix formation
(Predentin)

Collagen Ground

fibers substance

2 Maturation (mineralization)

Hydroxyapatite crystals

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

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

2- Mineralization

Budding of matrix vesicles
Rupture of matrix vesicles
Mineralization of the mantle dentin

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 number of dentinal tubules are fewer
Line of demarcation (dark).

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.
Subodontoblastic layer will differentiate and replace the degenerated odontoblasts to form reparative dentin

Irregular D T

Types Of Reparative Dentin

Atubular dentin ( area without dentinal tubules)

Osteodentin

Vasodentin

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 (setting of borders )

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

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 (destroy).

Trasparent D

Transparent D

Dead Tracts


Severe stimulation to dentin leads to destruction of the odontoblastic process and odontoblasts. This leads to empty and wide dentinal tubules.
These areas apear black with transmitted light.
Under the dead tracts from the pulpal surface , reparative dentine will be formed. (Blind tracts)

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