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Dentin DevelopmentOdontoblasts differentiation Early dentin formation
Life History Of Odontoblasts .Differentiation of odontoblasts -1 AmeloblastsPreameloblastsBasementmembraneDifferentiate from At first become the peripheral short columnar cell The cells grow in lengthdental papilla cells with many stubby (40u) and closely packed (UMC) together processes
Formation of the predentin -2Odontoblast become a protein forming and secreting cell.• R E R , Mitochondria and Golgi bodies• Ribonucleic acid and alkaline phosphataseLarge openfaced N Inner dental RER epith sideMitochondria Golgi Predentin bodies
Odontoblastic process formation -3 As more D is laid down, theAt first more than one cells receed and leave singleprocess process ( Tomes’ fiber)
Quiescent state of odontoblasts -4 The odontoblasts decrease in size and form dentin in a slowly diminishing rate until stimulated to form reparative dentin.
Matrix formation -1• A- Mantle dentin Fibers are perpendicular to D E J• The first formed dentinlayer in crown• And root 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 Crown Root Circumpulpal dentin• Thickness: 10-20 um • Thickness: bulk of the tooth• Diameter of collagen • Diameter of collagen fibers: fibers: large (0.1-0.2 um) small (0.05um)• Direction of collagen • Direction of collagen fibers : fibers : have right angle have right or oblique angle to to DEJ and parallel to dentinal tubules (parallel to basement membrane in dentin surface) root • Ground substance: from• Ground substance: from odontoblasts odontoblasts and the • Mineralization: Globular cell free zone below mantle dentin then• Mineralization: linear become mixed in the form (contains matrix remaining circumpulpal vesicles). dentin (no M V ).
Mineralization -2Budding of matrix Rupture of matrix Mineralization of the vesicles vesicles mantle dentin Has membrane rich in alkalineMatrix phosphatasvesicle e Calcium and phosphate ions undergo crystallization
Pattern Of Mineralization 1- Linear at the mantle dentin area 2- Globular in M V in Crystal matrix circumpulpal lization dentin just below mantle dentin 3- Combination in the remainingLodgment circumpulpal Ruptureof crystals 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).
Irregular Secondary Dentin (Reparative-2 (or tertiary dentin• Severe stimulus• The dentin is formed at a localized area.• The dentinal tubules are less in number and irregular in Irregular D T arrangement.• UMC from the subodontoblastic layer will differentiate and replace the degenerated odontoblasts to form reparative dentin
Thus Secondary Dentin may be:• Regular • Irregular• Cause: Mild stimuli (slow attrition and Severe stimulus (abrasion, slowly progressing caries) erosion, severe attrition and Site of formation: deep caries)Occurs on the entire pulpal surface of the tooth ( thicker Formed at the area on the roof and floor of the corresponding to the pulpal pulp chamber in multirooted end of the exposed dentin. teeth). Dentinal tubules: - Have irregular or twisted- Change their direction and course have more wavy course- They decrease in number per - unit area. They decrease in number and some areas may have no tubules Line of demarcation (a tubular dentin).Present and stained dark. May or may not present
• Clinically:• The decrease of the • The localized area of pulp chamber height dentin formation and obliteration of increase the time the pulp horns make taken by caries to the liability of pulp reach the pulp exposure during (barrier) cavity preparation much less likely to occur
(Transparent (Sclerotic Dentin -3Mild stimulus leads to changesin 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 3- Then the DT peritubular dentin. become obliterated.The affected area have occluded dentinal tubules, sothe dentin have uniform refractive index. So this areaof dentin appear translucent by transmitted light.
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 andtheir histological features.•Predentin•Primary dentin (mantle, circumpulpal, peritubular, intertubular and interglobulardentin) Regular Atubular dentin•Secondary dentin Irregular Vasodentin Osteodentin•Sclerotic dentin