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  • Collagen type I acts as a scaffold tht accommodates a large proportion(app. 56%) of the mineral in the holes and pores of fibrils.Noncollagenous matrix proteins pack the space between collagen fbrils and accumulate along the periphery of dentinal tubules.Thy regulate mineral deposition and can act as inhibitor, promoter, and/or stabilizer; their distribution is suggestive of their role. These proteins are DPP, DSP, DGP, dentin matrix protein-1(DMP-1), bone sialoprotein (BSP) osteopontin, osteonecin.DPP DSP DGP are expressed at gene level as a single molecule called dentin sialophosphoprotein (DSPP) that is then processed into individual components with distinct physiochemical properties.
  • Thus d DP is the formative organ of dentin and eventually becomes the pulp of the tooth.
  • The DP cells are small and undifferentiated , and they exhibit a central nucleus and few organelles.At this tym they r seperated from IEE by an acellular zone that contian some fine collagen fibrils.The ectomesenchymal cells adjoining the acellular zone rapidly enlarge and elongate to become preodontoblast first and thnodontoblast as their cytoplas increases in vol to contain inceasingamt of protein-synthesizing organells.The acellular zone b/w BP and IEE gradually is eliminated as the odontoblast differentiate and increase in size and occupy this zone.These newly differentiated cells are charecterized by being highly polarized , with theirnuclei positioned away from the IEE.
  • korff’sfiber have been described as the initial dentin deposition along the cusp tip.These fiber consist of collagen typ III associated , with fibronectin. The odontoblast process or Tomes’ fiber, left behind in the forming dentin matrix as the odontoblast moves away toward the pulp
  • Globular calcification involves the deposition of crystals in several discrete areas of matrix by heterogenous capture in collagen. with continued crystal growth , globular masses are formed that continue to enlarge and eventually fuse to form a single calcified mass. This pattern of mineralization is best scene in mantle dentin region, where matrix vesicles give rise to mineralization foci that grow and coalesce.In circumpulpal dentin minerlization front can progress in a globular or lenear pattern .Size of globule seems to depends on the rate of dentin deposition, with the largest globules occuring where dentin deposition is fastest.When the rate of formation progresses slowly , the mineralization front appears more uniform and the process is said to be linear.Occurs by globular/calcospheric calcification  deposition of crystals in several discrete areas at a time.Continued crystal growth forms globular masses which coalesce to form a single calcified mass.Seen in circumpulpal dentin.When these globular masses do not completely fuse, small areas of uncalcified matrix are left – Interglobular dentin
  • From that point , dentin formation spreads down the cusp slope as far as the cervical loop of enamel organ, and the dentin thickens until all the coronal dentin is formed.The onset of root formation proceeds the onset of tooth eruption.By the tym tooth reaches to its functional position, about 2/3rd of root dentin will hav been formed.Completion of root dentin formation does not occur in deciduoud tooth untillabt 18 mnts after it erupts and in permanent tooth untill 2-3 yrs after it eruptDentin formation continuous through out the life of the tooth, and its formation results in gradual but progressive reduction in size of pulp cavity.
  • Dentin is harder in permanent teeth than in deciduous teeth. Dentin becomes harder with age, primarily due to increase in mineral content
  • Hydroxyapatite crystals, which average 0.1µm in length, are formed along the fibers with their long axis oriented parallel to the collagen fiber.
  • It is seen most frequently incircumpulpal dentinIt is defect in mineralization pattern , not in matrix pattern ,normal architechtural pattern of the tubule remain unchanged , and they run unitturuped through the interglobular areas.
  • A progressive increase in granularity from CEJ to the apex of tooth.It found only in root dentin , and seen only because of light reflection in thick ground section.More recent interpretation relates this layer to a special arrangement of collagen and non-collagenous matrix proteins at the interface between dentin and cementum.C. These lines are not incremental lines of von Ebner, but rather contour lines of Owen. They reflect a major interruption in the deposition of dentin due to a metabolic distruption during odontogenesis
  • They run at right angles to the dentinal tubules.These lines reflect the daily rhythmicdeposition of dentin matrix as well as a hesitation in the daily formative process. The distance between them varies from 4 to 8µm in the crown to much less in the root. spherical configurationThese are the incremental lines of von Ebner. This is a ground section, but these lines can also be seen in demineralized sections. The lines of von Ebner represent cyclic activity of the odontoblasts during dentin formation. These incremental lines illustrate the daily pattern of dentin deposition that progresses at about 6 µm per day in the crown and about 3.5 µm per day in the root.
  • The rounded projections of enamel fit into the shallow depressions of dentin. This interdigitation seems to contribute to a firm attachment between dentin and enamel.
  • 1.The attachment of cementum to dentin in either case is quite firm although the nature of this attachment is not fully understood. 2.Predentin-pulp junction is made up of dense collageneousfibers and is present between the uncalcified dentin (predentin) and pulp. 3.Dentin-Predentin junction is the interface between the calcified and uncalcified newly formed dentin called predentin.
  • Pulp recession can be readily detected on radiographs and is important in determining the form of cavity preparation for restorative procedures
  • These dead tracts appear dark in ground section in transmitted light and white in reflected light.Blind tracts appear white in transmitted light.the dentin in blind trcs is called sclerotic dentin.The adaptive advantageof blind tracts is the sealing off of dentinal tubules to prevent bacteria from entering the pulp cavity.Their disintegation is often observed in the area of narrow pulpal horn, bcoz of crowding of odontoblast.Again where repairative dentin seals dentinal tubbules at their pulpal ends, dentinal tubules fill with fluid or gaseous substance.
  • This structural appearance of the dentinal tubule in the primary tooth dentin may be one of the factors contributing to the faster progression of caries
  • While it’s a gud protective barrier, it has relatively weak attachment to the dentin and is subject to dissolution by acids.Its removal during canal prepration increases the quality of seal between endodontic filling materials and root dentinIt may also increses the bond strength of resin posts.
  • Is done for the purpose of removal of smear layer and demineralization of dentin by which microporosities are exposed on dentinal surface.

    1. 1. Presentation by: Garima singh 1st yr PG Dentin 1
    2. 2. • Primary dentin Vs permanent dentin • Infected dentin Vs affected dentin • Smear layer • Dentin bonding system • Conclusion • References • Introduction • Composition of dentin • Dentinogenesis • Physical properties of dentin • Histology of dentin • Types of dentin • Innnervation of dentin • Age and functional changes Contents : 2
    3. 3. • Dentin is a mineralized, elastic, yellowish- white, avascular tissue enclosing the central pulp chamber. • Dentin is characterized by multiple closely packed dentinal tubules that traverse its entire thickness and contain the cytoplasmic extensions of odontoblasts that once formed the dentin and then maintain it. Introduction 3
    4. 4. • Inorganic material 70% – Consist of hydroxyapatite in form of small plates • Organic material 20% – It is about 90% collagen (mainly type I with small amount of type III and type V) – noncollagenous matrix proteins and lipids • Water 10% Composition of dentin 4
    5. 5. • It is a two phase sequence – collagen matrix formation – Mineralization • Outlines are – Differentiation of odontoblast – Formation of mantle predentin – Mineralization Dentinogenesis 5
    6. 6. • Differentiation of odontoblast is brought about by the expression of signaling molecule and growth factors in cells of IEE Odontoblast differentiation 6
    7. 7. • The first sign of dentin formation is the appearance of distinct, large-diameter collagen fibrils (0.1-0.2 mm in dia) called von Korff’s fibres. • As odontoblast continue to increases in size, they also produce smaller collagen type I fibrils that orient themselves parallel to future DEJ. • In this way a layer of mantle predentin appears. Fromation of mentle predentin 7
    8. 8. • Throughout dentinogenesis, mineralization is achieved by continuous deposition of mineral, initially in the matrix vesicle and then at the mineralization front. • Factors :‽ • Proteins are : – Dentin phosphoprotien (DPP)- key protein – Osteonectin-inhibitory effect – Osteopontin- promoter – Gla protein- seeder / nucleaator – Chondrointin sulphate- Mineralization 8
    9. 9. • Two pattern: 1) Globular mineralization Deposiotion of crystals in several discrete areas of matrix by heterogenous capture in collagen. 2) Linear mineralization When the rate of formation progresses slow, the mineralization front appears more uniform. Pattern of mineralization Scanning electron micrograph of globular dentin 9
    10. 10. • Dentin formation begins at the bell stage of tooth development in tissue adjacent to concave tip of the folded inner enamel epithilium.(it is the site where cuspal development begins. • Root dentin forms at a slightly later stage of development. • requires the proliferation of epitilial cells ( hertwig’s epithelial root sheath) from the cervical loop of enamel organ around growing pulp to initiate the differentiation of root odontoblast. Pattern of dentin formation 10
    11. 11. • Many genes are implicated in dentinogenesis, the newer ones being – MAP1B for odontoblast differentiation, and – PHEX for dentin mineralization Genetic regulation of dentinogenesis Kaneko T, Arayatrakoollikit U, Yamanaka Y, Ito T, Okiji T. Immunohistochemical and gene expression analysis of stem-cell-associated markers in rat dental pulp. Cell and tissue research. 2013 ; 351 (3): 425-432. 11
    12. 12. • Color : Pale yellow in deciduous teeth ,Yellow in permanent dentition. Light passes through thin, highly mineralized enamel and is reflected by underlying dentin. Thicker or hypomineralized enamel does not permit light to pass through readily. • Thickness of dentin: Range: 3-10mm Ratio of thickness in primary and permanent teeth is 1:2 Physical properties of dentin 12
    13. 13. • Hardness: Dentin is softer than enamel but more hard than bone or cementum. Hardness of dentin is one fifth (1/5th ) that of enamel; near the DEJ it is three times greater than near the pulp. • The compressive strength of dentin is 217-300 MPa which is much higher than enamel. 13
    14. 14. • Modulus of elasticity of dentin is 1.67x 10⁶ PSI. • Tensile strength of dentin is approx. 40MPa , which is less than cortical bone and approx one half (1/2) that of enamel. 14
    15. 15. • Extend through entire thickness of dentin from DEJ to pulp. • ‘S’-shaped path from the outer surface of the dentin to the perimeter of the pulp in coronal dentin. • Less pronounced in root dentin in the cervical third and in incisal edges and cusps . • Straight in deciduous teeth. Histology of dentin Dentinal tubule: 15
    16. 16. • Diameter of dentinal tubules : – Larger in diameter near pulp - 3 to 4µm, and smaller at the DEJ- 1µm. • Number of Dentinal tubules : – At the pulpal surface of dentin the number /sq mm varies between 50,000 & 90,000. – At DEJ : 8000- 15,000 • More tubules per unit area in the crown than in the root. 16
    17. 17. • The dentin that immediately surrounds the dentinal tubules is termed peritubular dentin. • This dentin forms the walls of the tubules. • It is highly mineralized (about 9% more) than intertubular dentin. – The formation of intratubular dentin is a slow continuing process causing reduction in size of lumen. Peritubular dentin/ intratubular dentin: 17
    18. 18. • The main body of dentin is composed of intertubular dentin. • It is located between the dental tubules more specifically, between the zones of peritubular dentin. • About one half of its volume is organic matrix, specifically collagen fibers which are randomly oriented around the dentinal tubules. Inter-tubular dentin: 18
    19. 19. • It is term used to describe areas of unmineralized or hypo mineralized dentin where globular zones of mineralization (calcospherites) have failed to fuse into a homogenous mass within mature dentin. • These areas are prevelent especially in person which has had a deficiency in vit D or exposure to high level of fluoride at the time of dentin formation. Inter globular dentin: 19
    20. 20. • When root dentin is viewed under transmitted light in ground section , a granular- appearing area, the granular layer of Tomes, can be seen just below the surface of the dentin where the root is covered by cementum. • Caused by a coalescing and looping of the terminal branches of the dentinal tubules. These areas remain unmineralized. Granular layer of TOMES: 20
    21. 21. • Incremental lines of von Ebner appear as fine lines or striationsion. • A that reflect rhythmic dentin deposition are more distinctly visualized in this demineralized section. • B is devoid of such lines. This is a characteristic of mantle dentin. • C that reflects the spherule- like mineralization pattern of dentin. Incremental/Imbrication Lines of von Ebner 21
    22. 22. Dentinoenamel junction: • Unique bond between two very dissimilar materials. • It is scalloped or pitted or wavy in outline, with the crest of the waves penetrating towards the enamel. • Function- prevention of delamination. Dentinal junction Shimizu D, Macho A. functional significance of microstructral detail of the primate dentino- enamel junction: A possible example of exaptation. J Hum Evol. 2007;52 :103-111. 22
    23. 23. Dentino-cemental junction: • There is a smooth line junction between the dentin and cementum in permanent teeth. • The cemento-dentinal junction in deciduous teeth is sometimes scalloped. 23
    24. 24. • In human teeth three types of dentin can be recognized– – Primary dentin – Secondary dentin – Tertiary dentin Types of dentin 24
    25. 25. Primary Dentin- • Formed prior to the eruption of the teeth and root completion. • Major bulk of dentin. • It is composed of Mantle dentin and Circumpulpal dentin. • Completed 2-3 years after tooth eruption for permanent teeth and 18 months for deciduous teeth. 25
    26. 26. Mantle Dentin- • The first-formed dentin in the crown underlying the DEJ. • Large collagen fibrils perpendicular to DEJ (0.1- 0.2µm in diameter) : argyrophilic or silver-stained and called von Korffs fibers. • 4% less mineralized than circumpulpal dentin. Circumpulpal Dentin- • Forms bulk of the tooth. • Formed prior to root completion. • Smaller collagen fibrils (0.05µm in diameter); more closely packed together. 26
    27. 27. Secondary dentin- • Formed after completion of root formation. • Continuing, but much slower deposition of dentin. • Narrow band of dentin bordering the pulp. • Contains fewer tubules than primary dentin. 27
    28. 28. • Greater deposition of secondary dentin on the roof and floor of the pulp chamber leads to an asymmetric reduction in size and shape of the chamber and the pulp horns. • The tubules of secondary dentin undergo sclerosis more readily than primary dentin. • This process tends to reduce the overall permeability of the dentin and thereby to protect the pulp. 28
    29. 29. Tertiary dentin- • Tertiary dentin is also known as Reactive, Reparative or Irregular secondary dentin. • It is the dentin that is formed in response to abnormal stimuli such as attrition, abrasion, erosion, trauma, moderate dentinal caries and restorative materials. 29
    30. 30. • Usually appears as a localized dentin deposit on the wall of the pulp cavity immediately subjacent to the area on the tooth that has received the injury (dentin deposits underneath the affected tubules). • Types of tertiary dentin: Reactionary dentin Reparative dentin 30
    31. 31. Reactionary dentin: • When the original odontoblasts that made secondary dentin are responsible for focal tertiary dentin formation. • Rate of formation of dentin is increased. • Tubules remain continuous with the secondary dentin. 31
    32. 32. Reparative dentin: • If the provoking stimulus causes destruction of the original odontoblasts, the newly differentiated odontoblast -like cells secrete less tubular, more irregular dentin called Reparative dentin. • Here, tubules are usually not continuous with those of secondary dentin. 32
    33. 33. • Nerve fibers were shown to accompany 30-70% odontoblastic process, and these are reffered to as intratubular nerves. • Nerve and their terminal are found in close association with odontoblast process withih tubules • It is believed that most of these are terminal processes of mylinated nere fibers of dental pulp. Innervation of dentin: 33
    34. 34. • 3 basic theories of pain conduction through dentin are: • Direct neural stimulation: by which the nerve in dentin get stimulated. • Transduction theory: which presumes that the odontoblast process is primary structure excited by the stimulus and that impulse is transmittes to the nerve endings in inner dentin. Theories of pain transmission through dentin 34
    35. 35. • Hydrodynamic theory: various stimuli affect fluid movement in dentinal tubule. • This fluid movement , either inward/ outward stimulates pain mechanism in tubules by mechanical distribution of nerves closely associated with the odontoblast and its process. • Thus these endings may act as mechanoreceptors as they are affeced by mechanical displacement of tubular fluid. • 35
    36. 36. • Dead tracts and blind tract: • When dentin is damaged, odontoblastic processes die or retract leaving empty dentinal tubules. These areas with empty dentinal tubules are called dead tracts. • With time these tracts can become completely filled with mineral. This region is called blind tracts. Age and functional changes: 36
    37. 37. • Longitudinal ground section of permanent teeth dentin showed DT following an ‚S‛-shaped curve, where as in primary DT follow a straight curve. • Density of innervation is less in primary teeth as compare to the permanent teeth. Primary dentin and permanent dentin Chowdhary N ,Subba Reddy VV. Dentin comparison in primary and permanent molars under transmitted and polarised light microscopy: An in vitro study. J Indian Soc Pedod Prev Dent. 2010; vol 28(3) : 167-172 37
    38. 38. • Primary tooth showing incremental lines at an angle to the dentinal tubules, whereas permanent tooth showing incremental lines at right angles to the dentinal tubules 38
    39. 39. • Infected dentin: Superficial layer which is soft and leathery in consistency and dark brown in color. – It has a high concentration of bacteria and collagen is irreversibly denatured . – It is not remineralizable and must be removed • Affected dentin: Deeper layer which is hard in consistency and light brown in color. – It does not contain bacteria and is reversibly denatured. Therefore this layer preserved Infected dentin & affected dentin 39
    40. 40. • Whenever dentin has been cut or abraded, a thin altered layer is created on the surface. • Composed of denatured collagen, hydroxyapatite and other cutting debris. • Serves as a bandage over the cut dentinal surface because it occludes many of dentinal tubules with debris called smear plugs. • Clinical significance : Smear layer 40
    41. 41. • The fundamental principle of adhesion to tooth substrate is based upon an exchange process by which inorganic tooth material is exchanged for synthetic resin. • This process involves 2 phases 1. Etching of tooth surface, 2. Hybridization phase • Clinical relevance of etching time on dentin demineralization: Dentin bonding system 41 Perdigấo J, Lopes M. The effect of etching time on dentin demineralization. Quintessence int.2001 ; 32:19-26.
    42. 42. 42 Clinical implications: • Dental caries • Dentin hypersentivity • Dentinogenesis imperfecta • Dentin dysplasia
    43. 43. • Dentin is a living tissue. It is covered by enamel in crown portion and by cementum in root portion. • It will become sensitive if covering of either enamel or cementum will lost due to any reason. • So, all efforts should be made during restorative procedures to preserve as much healthy dentinal tissue as possible. Conclusion 43
    44. 44. • Chowdhary N ,Subba Reddy VV. Dentin comparison in primary and permanent molars under transmitted and polarised light microscopy: An in vitro study. J Indian Soc Pedod Prev Dent. 2010; vol 28(3) : 167-172 • Kaneko T, Arayatrakoollikit U, Yamanaka Y, Ito T, Okiji T. Immunohistochemical and gene expression analysis of stem-cell- associated markers in rat dental pulp. Cell and tissue research. 2013 ; 351 (3): 425-432. • Shimizu D, Macho A. functional significance of microstructral detail of the primate dentino-enamel junction: A possible example of exaptation. J Hum Evol. 2007;52 :103-111. • infected.html References 44
    45. 45. • Gallagher R, Balooch M, Balooch G, Wilson R, Marshall S, Marshall G. Coupled nanomechanical and Raman microspectroscopic investigation od human third molar dentinoenamel junction. J Dent Biomech. 2010;1:1-4. • Perdigấo J, Lopes M. The effect of etching time on dentin demineralization. Quintessence int.2001 ; 32:19-26. • Nanci A. Tencate’s Oral histology. 8th ed. 2013 • Kumar GS. Orban’s oral histology and embryology. 12th ed. India: Elsevier, 2009 45
    46. 46. 46