Tooth Dentin and dentinogenesis ppt
- 6. Dentin Pulp
- 7. Provides the bulk and general form of tooth. Determines the shape of the crown. Physically & chemically the dentin closely resembles the bone. The main morphologic difference between bone & dentin is that some of the osteoblasts that form bone marrow enclosed within its matrix substance as osteocytes, whereas the dentin contains only the processes of the cells that form it. Both are considered vital tissue because they contain because they contain living protoplasm. DENTINDENTIN
- 9. • It is light yellowish in color, becoming darker with age. • It is elastic and subject to slight deformation. • Harder than bone but softer than enamel. • Lower content of mineral salts in dentin renders it more radiolucent than enamel.
- 10. Consists of 35% organic matter and water & 65% inorganic material. The organic substance consists of collagenous fibrils and a ground substance of mucopolysaccharides (proteoglycans and glycos aminoglycans). The inorganic component consists of hydroxyapetite as in bone, cementum & enamel. Organic constituents can be removed from the mineral by incineration or organic chelation.
- 11. • The bodies of the odontoblasts are arranged in a layer on the pulpal surface of the dentin, and only their cytoplasmic processes are included in the tubules in the mineralized matrix.
- 12. •Each cell gives rise to one process, which traverses the predentin & calcified dentin within one tubule.
- 13. •Terminates in a branching network at the junction with enamel or cementum. •Tubules are found throughout normal dentin & are therefore characteristic of it.
- 14. • The course follows a gentle curve in the crown, less so in the root, where it resembles S in shape.
- 15. • Starting at right angles from the pulpal surface, the first convexity of this doubly curved course is directed toward the apex of the tooth. • Near the root tip & along the incisal edges and cusps the tubules are almost straight.
- 16. •These tubules end perpendicular to the dentinoenamel and dentinocementum junctions.
- 17. • The ratio between the outer and inner surfaces of dentin is about 5:1. • The ratio between the numbers of tubules per unit area on the pulpal and outer surfaces of dentin is about 4:1.
- 18. • There are more tubules per unit area in the crown than in the root. • The dentinal tubules have lateral branches throughout dentin, which are termed canaliculi or microtubules. • A few dentinal tubules extend through the dentinoenamel junction into the enamel. These are termed enamel spindles.
- 20. Types of DentinTypes of Dentin Dentin Primary physiologic dentin Secondary physiologic dentin Tertiary dentin or reparative dentin or reactionary dentin or irregular secondary dentin Mantle dentin Circumpulpal dentin Peritubular dentin Intertubular dentin
- 21. The dentin that immediately surrounds the dentinal tubules. It is more highly mineralized than intertubular dentin. It is twice as thick in outer dentin (approx. 0.75um) than in inner dentin (0.4um). By its growth, it constricts the dentinal tubules to a diameter of 1um near the dentinoenamel junction. Organic matrix is lost along with mineral after decalcification. The calcified tubule wall has an inner organic lining termed the lamina limitans, high in glucosaminoglycans (GAG).
- 23. • Forms the main body of dentin. • It is located between the dentinal tubules or, more specifically, between the zones of peritubular dentin. • Its organic matrix is retained after decalcification. • About one-half of its volume is organic matrix, specifically collagen fibers. The fibrils range from 0.5 to 0.2um in diameter and exhibit crossbanding at 64um intervals, which is typical for collagen.
- 25. Dentinal tubules Peritubular dentin Intertubular dentin
- 26. Dentinal tubules Peritubular dentin Intertubular dentin
- 27. Is located adjacent to the pulp tissue. Is 2 to 6 um wide, depending on the activity of the odontoblast. It is the first formed dentin and is not mineralized. As the collagen fibers undergo mineralization at the predentin- dentin front, the predentin then becomes dentin and a new layer of predentin forms circumpulpally.
- 28. They are the cytoplasmic extensions of the odontoblasts. The odontoblasts reside in the peripheral pulp at the pulp- predentin border and their processes extend into the dentinal tubules. The processes are largest in diameter near the pulp and taper further into dentin. The odontoblast cell bodies are approximately 7um in diameter and 40um in length.
- 29. Odontoblasts and processOdontoblasts and process Odontoblast cellsOdontoblast process Dentin Pulp
- 31. • Mantle dentin is the first formed dentin in the crown underlying the dentinoenamel junction. • It is the outer or most peripheral part of the primary dentin & is about 20um thick. • The fibrils found in this zone are perpendicular to the dentinoenamel junction. • Circumpulpal dentin forms the remaining primary dentin or bulk of the tooth. • Represents all of the dentin formed prior to root completion. • The fibrils are much smaller in diameter & are more closely packed together. • Slightly more mineral content than mantle dentin.
- 33. A narrow band of dentin bordering the pulp and representing the dentin formed after root completion. Contains fewer tubules than primary dentin. There is usually a bend in the tubules where primary and secondary dentin interface.
- 35. The incremental lines of von ebner, or imbrication lines, appear as fine lines or striations in dentin. They run at right angles to the dentinal tubules. These lines reflect the daily rhythmic, recurrent deposition of dentin matrix as well as hesitation in the daily formative process. The course of the lines indicates the growth pattern of the dentin. Some of the incremental lines are accentuated because of disturbances in the matrix and mineralization process. Such lines are known as contour lines of owen.
- 39. These lines represent hypocalcified bands. In the deciduous teeth and in the first permanent molars, the prenatal and postnatal dentin is separated by an accentuated contour line. This is termed the neonatal line. This line reflects the abrupt change in environment that occurs at birth. The dentin matrix formed prior to birth is usually of better quality than that formed after birth.
- 41. • Sometimes mineralization of dentin begins in small globular areas that fail to fuse into a homogenous mass. This results in zones of hypomineralization between the globules. These zones are called interglobular dentin. • Forms in crowns of teeth in the circumpulpal dentin just below the mantle dentin. • Follows an incremental pattern. • The dentinal tubules pass uninterruptedly, thus demonstrating a defect of mineralization & not of matrix formation.
- 44. There is a zone adjacent to the cementum that appears granular. This is known as ‘Tomes granular layer’. Slightly increases in amount from the cementoenamel junction to the root apex. Caused by coalescing and looping of the terminal portions of the dentinal tubules.
- 47. Odontoblasts differentiation Early dentin formation
- 48. 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
- 51. Odontoblast become a protein forming and secreting cell. R E R , Mitochondria and Golgi bodies Ribonucleic acid and alkaline phosphatase Inner epithelium side Large open faced Nucleus R E R Mitochondria Golgi bodies Predentin
- 52. At first more than one process As more Dentin is laid down, the cells recede and leave single process ( Tomes’ fiber)
- 53. The odontoblasts decrease in size and form dentin in a slowly diminishing rate until stimulated to form reparative dentin.
- 55. 1 Matrix formation (Predentin) Collagen Ground fibers substance 2 Mineralization Hydroxyapatite crystals
- 57. A- Mantle dentin The first formed dentin layer in crown And root Fibers are perpendicular to D EJ Fibers are parallel to basement membrane
- 58. 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
- 59. 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 Crown Root
- 60. 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
- 61. M V in matrix Crystal lization 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
- 62. 1-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).
- 63. 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
- 64. Atubular dentin ( area without dentinal tubules) Osteodentin (entrapped cells). Vasodentin (entrapped b.v.)
- 65. 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
- 66. 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)
- 67. 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.
- 68. Trasparent D
- 69. 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.
- 70. • Direct conduction theory in which stimuli directly effect the nerve endings in the tubules. • Transduction theory in which the membrane of the odontoblast process conducts an impulse to the nerve endings in the predentin, odontoblast zone, and pulp. • Fluid or hydrodynamic theory in which stimuli cause an inward or outward movement of fluid in the tubule, which in turn produces movement of the odontoblast and its processes.
- 72. • The rapid penetration & spread of caries in the dentin is the result of the tubule system in the dentin. • The dentinal tubules form a passage for invading bacteria that may thus reach the pulp through a thick dentinal layer. • Air driven cutting instruments cause dislodgement of the odontoblasts from the periphery of the pulp & their aspiration within the dentinal tubule. • Sensitivity of dentin.
- 73. • Infected dentine is the outer layer and is softened and contaminated with bacteria. It is irreversibly denatured and not remineralized • Affected dentine has a demineralized phase, but not yet invaded by bacteria. It can be remineralized. • In clinical restorative treatment of dentine during cavity preparation it is infected dentine which is completely removed. The affected dentine, which may be remineralized after the completion of restorative treatment, is not removed and is preserved.
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