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 Odonto blasts 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) Periodontobl astic 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

III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 IIIIn badly formed tooth it appears in the root dentin TTT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 differentiationEarly dentin formation

Life Cycle Of Odontoblasts 1- Differentiation 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 1 Matrix formation (Predentin) (Predentin) Collagen Ground fibers substance 2 Maturation (mineralization) 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: um  Diameter of collagen fibers: large ( 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  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) 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) 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)