Dentin Development

Odontoblasts differentiation Early dentin formation

Life History Of Odontoblasts 1 -Differentiation of odontoblasts.

Differentiate from the peripheral

dental papilla cells (UMC)

At first become short columnar cell with many stubby

processes

Preameloblasts

Basement membrane

The cells grow in length (40u) and closely packed

together

Ameloblasts

Odontoblasts differentiation

2 -Formation of the predentinOdontoblast 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 rate until stimulated to form reparative dentin.

4 -Quiescent state of odontoblasts

Dentinogenesis

1 Matrix formation

(Predentin)

Collagen Ground

fibers substance

2 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

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

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 -MineralizationBudding 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

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

Age Changes Of Dentin1-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).

2-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

Types Of Reparative Dentin

Atubular dentin ( area without dentinal tubules)

Osteodentin (entrapped cells).

Vasodentin (entrapped b.v.)

Thus Secondary Dentin may be:

• 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 demarcationPresent 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

• 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)

3 -Transparent (Sclerotic Dentin)Mild stimulus leads to changes in 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 tubules, so the dentin have uniform refractive index. So this area of dentin appear translucent by transmitted light.

Trasparent D

4-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.

Discuss theories of pain transmission through dentin.

Compare between interglobular dentin and Tomes’ granular layer.

Compare between mantle and circumpulpal dentin.

Mention different types of secondary dentin and compare between them.

Mention different types of dentin and their histological features.

•Predentin

•Primary dentin (mantle, circumpulpal, peritubular, intertubular and interglobular dentin)

•Secondary dentin Regular

Irregular

Atubular dentin

Vasodentin

Osteodentin•Sclerotic dentin