Dental histology dentin chap4

1. 1

2. Physical properties
 Dentin forms the bulk of the tooth.
 Is the first formed amongst the dental hard tissues.
 Formation begins in the late bell stage.
 Formed by odontoblast cells.
 Dentin is yellow in color.
 It is elastic in nature.
 firmly bound to enamel at DEJ and to cementum at
CEJ.
2

3. COMPOSITION
Mature dentin
by weight
70% inorganic
20% organic
10%water
By volume
45% inorganic
33% organic
22% water
3

4. Inorganic
• hydroxyapatite crystals
Organic
• type 1 collagen
• traces of type3 and type5
• Traces of lipids and non collagenous matrix proteins
• Fractional inclusion of glycoproteins, proteoglycan
and phosphoproteins.
• Non collagenous matrix proteins comprise of
phosphoproteins, sialoproteins, dentin matrix
proteins1, osteonectin, osteocalcin, osteopoitin
Proteoglycans and some serum proteins.
4

5. BASIC ANATOMY
 Dentin is characterized by the presence of multiple
closely packed dentinal tubules that traverse its entire
thickness and contain the cytoplasmic extensions of
odontoblasts that once formed dentin and now
maintain it
 The cell bodies of odontoblasts are aligned along the
inner aspect of dentin, along the pulp
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6. 6

7. 7

8. TYPES OF DENTIN
 DENTIN CAN BE DIVIDED INTO
1)PRIMARY DENTIN
2)SECONDARY DENTIN
3)TERTIARY DENTIN
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9. 9

10. 10

11. 11

12. PRIMARY DENTIN
 It is further divided into
1)MANTLE DENTIN
2)CIRCUMPULPAL
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13. MANTLE DENTIN
 Is the first formed dentin
 in the crown underlies DEJ
 is about 150 μm wide
 fibrils formed in this zone are perpendicular to the
DEJ and organic matrix composed of larger collagen
fibrils
 Has fewer defects compared to circumpulpal dentin
CIRCUMPULPAL
 Outlines the pulp chamber
 Slightly more (4%) mineralized than mantle dentin.
13

14. SECONDARY DENTIN
• It’s a narrow band of dentin bordering the pulp
• This forms after root formation is complete
• Previously, it was believed that secondary dentin forms
in response to functional stimuli, but it is now
established it is a slow continous deposition of dentin
• Contains fewer tubules than primary dentin
• It is formed more slowly than primary dentin
• It is not formed uniformly
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15. 15

16.  Incremental pattern and tubular structure similar to
primary dentin
 It has the same organic and inorganic ratio
 Greater deposition on the roof and floor of the pulp
chamber.
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17. TERTIARY DENTIN
• Reactive, Reparative, Irregular dentin.
• Produced in reaction to various stimuli
• Produced at cells directly affected by stimulus
• Quality and quantity depends on intensity and duration
of stimulus
• Tubules may or may not be present
• Cells may be included in dentin referred to as
osteodentin
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18. 18

19. Predentin
 Layer of variable thickness - 100-47 μm.
 Lines the innermost portion of dentin, adjacent to the
pulp tissue .
 Unmineralized dentin matrix
 Consists of collagen, glycoproteins and proteoglycans
 Similar to osteoid in bone.
 Predentin is thickest where active dentinogenensis is
occurring.
 Presence is important in maintaining the integrity of
dentin.
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20. 20

21. 21

22. 22

23. RECENT CLASSIFICATION
1)Reactionary dentin
 deposited by preexisting odontoblasts
2)Reparative dentin
 deposited by newly differentiated odontoblasts
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24. REACTIONARY &REPARATIVE
DENTIN
 If by extension abrasion, erosion, caries or operative
procedures, the odontoblast processes are exposed or
cut , the odontoblasts die or survive based on the
intensity of the injury.
 If they survive the dentin that is produced is called
reactionary or regenerated dentin.
 Those odontoblasts that are killed are replaced by
migration of undifferentiated cells arising in deeper
regions of the pulp to the dentin interface.
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25.  Its believed that the origin of the new odontoblast is
from cells in the cell-rich zone or from
undifferentiated perivascular cells deeper in the pulp.
 The newly differentiated odontoblasts then begin
deposition of reparative dentin.
 This action to seal off the zone of injury occurs as a
healing process initiated by the pulp, resulting in
resolution of the inflammatory process and removal of
dead cells.
 Reparative dentin is characterized by having fewer and
more twisted tubules than normal dentin.
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26. Fig: Diagrammatic representation of normal and
other types of reparative dentin
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27. DENTINOGENESIS
 Formation of dentin – Dentinogenesis
 Dentin is the first hard tissue to be
formed in the tooth.
 Cells responsible for the formation of
dentin are called Odontoblasts and they
are biologically related to osteoblasts.
 Dentinogenesis starts first at bell stage ,
at the cusp tips.
 Dentinogenesis occurs in two stages –
Matrix Formation and Mineralisation
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28. MINERALISATION
 Enamel , dentin and bone – major tissues developed
through matrix mediated mineralisation processes.
 Matrix of mantle dentin which gets mineralised before
enamel is secreted by ameloblasts. Matrix vesicles
from odontoblasts provide nucleation sites for
mineralisation of the mantle dentin to form outer
layer.
 While, the mineralistion of circumpulpal dentin
proceeds via spreading of deposition from preexisting
mineralised dentin matrix
28

29.  During dentinogenesis three different types of
mineralisation occurs:
- Cell derived matrix vesicles-driven
mineralisation(Mantle dentin)
- Extracellular matrix molecules – derived
mineralisation (Circumpulpal dentin)
- Serum derived precipitation (Peritubular dentin)
 Mineralisation of dentin (except intratubular dentin)
occurs in two patterns
- Linear
- Globular
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30. MATRIX FORMATION &ODONTOBLAST
DIFFERENTIATION
 Dentin matrix(predentin) formation begins at early
bell stage wherein the papilla differentiate into
odontoblasts.
 Signaling molecules and growth factors such as
fibronectin, decorin , laminin and chindroitin sulfate
in the dental papilla are responsible for odontoblast
differentiation.
 Dental papilla cells undergo certain number of mitosis
to differentiate into odontoblasts .
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31.  Odontoblastic differentiation is characterised by
cessation of cell division, changes in cell size and
shape , polarisation of nuclei and increase in organelle
count.
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32. DENTINOGENESIS
VITAL FEATURES REQUIRED FOR DENTINOGENISIS
 Odontoblast Differentiation
 Matrix Formation
 Good Vascular Supply
 Mineralization
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33. 33

34. ODONTOBLAST DIFFERENTIATION
 Differentiation of odontoblast brought about by
signalling molecules and growth factors in the cells of
IEE.
 At this time dental papilla cells are small and
undifferentiated exhibiting central nucleus and few
organelles
 Acellular zone is present in between
 cells adjoining the acellular zone enlarge and elongate
first to form preodontoblast and later odontoblast
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35. 35

36.  Acellular zone is gradually oblitrated as odontoblast
gradually increase in size after differentiating to
occupy this zone
 These newly differentiated cells are characterized by
being highly polarized, with their nuclei positioned
away from inner enamel epithelium
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37. 37

38. Organic matrix formation and
mineralization
 Organic matrix formation is as follows
 The first sign of dentin formation is the appearance of
distinct, large diameter collagen fibrils called Von
Korffs fibers
 Von Korffs fibers consist of collagen type3, they
originate deep among the odontoblasts, extends
towards IEE and fan out among the ground substance
immediately below the epithelium.
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39. Fig: Light micrograph of silver stain section of
early forming dentin.
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40. 40

41.  As the odontoblasts continue to increase in size, they
also produce smaller collagen type1 fibers that orient
themselves parallel to the future DEJ.
 In this way a layer of mantle dentin is formed.
 Immediately after deposition of collagen, the
odontoblasts adjacent to the IEE extends stubby
processes into the forming extracellular matrix.
41

42.  As the odontoblasts secrete matrix they increase in
size till the extracellular compartment between
them is obliterated.
 As the odontoblasts forms these stubby processes,
the odontoblasts bud off small membrane bound
vesicles called as matrix vesicles.
 They come to lie superficially near basement
membrane.
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43. 43

44.  The odontoblasts then develops a cell process, the
odontoblast process or tomes fiber, which is left behind
in the forming dentin matrix as the odontoblasts move
towards the pulp.
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45. 45

46. Mineralization
 Mineral phase appears first within the matrix vesicles
as single crystals believed to be seeded by
phospholipids present in the vesicle membrane
 Matrix vesicles contain calcium and phosphate ions,
alkaline phosphatase leading to formation of
hydroxyapatite crystals.
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47.  Crystals grow and rupture from the confines of vesicle
and spread as a cluster of crystallites, these fuse with
adjacent clusters and form mineralized matrix.
 Deposition of mineral lags behind matrix formation so
that a layer of organic matrix is always found between
odontoblasts and mineralization front called as
predentin.
 Following mineral seeding, non collagenous matrix
proteins come into play, in this way coronal mantle
dentin is formed
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48. 48

49. Formation of circumpulpal dentin
 After obliteration of extracellular compartment
 Organic matrix formed exclusively by odontoblasts
 Collagen formed is smaller and aligned at right
angles to odontoblastic processes
 Von korffs fibers absent
 Matrix vesicles no longer generated
 Addition of phosphoporyn unique to
circumpulpal dentin
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50. MINERALIZATION PATTERN
 Histologically 2 patterns seen
1. Globular calcification
2. Linear calcification
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51. Globular calcification
 Deposition of crystals in discrete areas of matrix by
heterogeneous capture in collagen, which enlarge and
eventually fuse to form single calcified mass.
 Example as in mantle dentin formation
Linear calcification
 Size of globules depends on deposition of dentin,
 largest globules forming - dentin deposition is fastest
 Example-circumpulpal dentin
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52. VASCULAR SUPPLY
 Good supply - imp during secretory phase
 Beginning of mantle dentin formation - capillaries are
seen in subodontoblastic area
 Circumpulpal dentin formation - capillaries migrate
between odontoblasts and endothelium fenestrates.
 After dentinogenisis is completed - capillaries retreat
and endothelial lining becomes continuous.
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53. 53

54. PREDENTIN
 Is located adjacent to the pulp tissue .
 Is a layer of variable thickness ranging from 10-47
micrometre wide
 Its unmineralised containing collagen and ground
substance
 Its thick in areas of active dentinogenesis
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55. 55

56. Histology of Predentin
 Microscopically, several structures seen like-
 dentinal tubules,
 intratubular dentin,
 intertubular dentin and
 interglobular dentin
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57. DENTINAL TUBULES
 Extend throughout the thickness of dentin
 They follow a S shaped path.
 Configuration indicates the course taken by
odontoblasts
 This is less pronounced in root dentin, cervical 1/3rd
and cusp tips.
 These are called primary curvatures resulting from
crowding of odontoblasts as they move towards the
pulp
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59. 59

60. 60

61. 61

62.  Smaller oscillations within primary curvatures are
called secondary curvatures.
 Tubules taper as they move from pulpal surface towards
DEJ.
 They are 2.5 µm in diameter at pulpal border
 1.2 µm at midportion
 900 nm at tip
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63. 63

64.  Their number ranges from 59000-76000/sqmm near
the pulp.
 Its half the number near enamel.
 Dentinal tubules have a anastomosing canalicular
system, mostly present at terminal portion and root
dentin.
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65. 65

66. INTRATUBULAR DENTIN
 It’s a hypermineralized ring of dentin within the dentinal tubule
 40% more mineralized than intertubular dentin
 Readily demonstrated in cross sections-ground and soft x-ray
analysis
 Originally called as peritubular dentin
 44nm at pulpal end
 750nm at DEJ.
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67. 67

68. SCLEROTIC DENTIN
 Dentinal tubules occluded by calcified material
 Dentin becomes glassy and translucent
 It increases with age and is common in apical 3rd of the
tooth
 Occlusion of tubules begin at 18 years of age without
any identifiable age
 Reduces the permeability of dentin and may help in
protecting pulp
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69. 69

70. INTERTUBULAR DENTIN
 Dentin in between the tubules is called intertubular
dentin
 Represents primary secretion of odontoblasts and
consists of tightly interwoven network of type1
collagen and hydroxyappatite crystals
 Crystals are parallel to the fibers.
 Fibers are arranged at right angles to the tubules
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71. 71

72. INTERGLOBULAR DENTIN
 Areas of unmineralized or hypomineralized areas
 Globular zones of mineralization fails to fuse with
mature dentin
 Mostly seen in circumpulpal dentin, just below mantle
dentin
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74. 74

75.  Defect seen in mineralization not matrix formation, so
tubules are normal
 No intatubular dentin is seen in these areas
 Is seen more in Vit - D deficiency and flourosis
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76. INCREMENTAL GROWTH LINES
 Dentinogenesis is characterized by period of activity
and quiescence, this is represented by incemental
growth lines.
 These lines run at right angles to tubules
 4 µm/day
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77. Incremental lines of von Ebner
 The 5 day rhythmic pattern, represented by lines are
called.
Contour lines of Owen
 Initially believed to be coincidence of secondary
curvatures
 But now believed to be caused by deficiencies of
mineralization.

78. 78

79. TOMES GRANULAR LAYER
 Its found near dentinocemental junction
 Its seen to progressively increase from CEJ to the apex
of the tooth
 This we observe because sections are made through
the looped terminal portions of dentinal tubules seen
in root dentin
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80. 80

81. DENTINOENAMEL JUNCTION
 Its found in the form of series of scallops
 SEM reveals it to be a series of ridges which increases
the adherence between dentin and enamel
 More pronounced in coronal dentin where occlusal
stress is more.
 Shape and nature prevents shearing of enamel
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82. 82

83. 83

84. DENTINOCEMENTAL JUNCTION
 Its peripheral to the granular layer of tomes
 It’s a thin structureless layer
 No scalloping seen
 The junction is relatively straight
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85. 85

86. DENTIN SENSITIVITY
 It’s a most unusual feature of pulp-dentin complex
 Among numerous stimuli that can evoke a painful
response are
 cold air or water
 mechanical contact by probe or bur
 by dehydration
 3 HYPOTHESIS
86

87. 1) DIRECT INNERVATION THEORY
 It says the dentin contains nerve endings that
respond when stimulated
DRAW BACKS
 Although the nerves in odontoblasts control the
activity of odontoblasts, they usually do not monitor
change in environment.
 Although some nerves within some tubules may cause
sensitivity but it does not solely depend on
stimulation of nerve endings.
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88. 88

89. 2) HYDRODYNAMIC THEORY
 The tubular nature of dentin permits fluid
movement to occur within the tubule when a
stimulus is applied, the movement is registered
by free nerve endings.
 This movement distorts local pulpal environment and
is sensed by nerve endings in plexus of Raschow.
 when dentin is cut this fluid escapes which causes
pain.
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90. 90

91. 3) MECHANORECEPTOR THEORY
 The odontoblasts serve as receptors and are
coupled to nerves in the pulp.
 This mechanism states that odontoblasts as a receptor
cell is of neural crest origin which retains an ability to
transduce and propagate an impulse.
DRAW BACKS
 But lack of synaptic response and low membrane
potential are against this theory.
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92. 92

93. Age changes
 Dentin is a vital tissue that is laid down throughout
life.
 Although after the teeth have erupted and have been
functioning for a short time , dentinogenesis slows and
further dentin formation is at a much slower rate.This
is the secondary dentin.
 Pathologic effect of dental caries, abrasion, attrition or
the cutting of the dentin for operative procedures
causes changes in dentin and these are described as
development of dead tracts, scelerosis and addition of
reparative dentin.

94. DEAD TRACTS
 Loss of odontoblast may occur in teeth containing vital
pulp as a result of caries, abrasion, attrition, cavity
preparation or erosion.
 Reparative dentin seals the dentinal tubules at their
pulpal ends, dentinal tubules filled with fluid or gaseous
substances.
 In ground sections such groups of tubules may entrap air
and appear black in transmitted and white in reflected
light.
 Dentin areas characterized by degenerated odontoblast
processes give rise to dead tracts which are probably the
initial step in formation of sclerotic dentin.
94

97. CLINICAL CONSIDERATION
 The cells of the exposed dentin should not be insulted by
bacterial toxins, strong drugs, undue operative trauma,
unnecessary thermal changes or irritating restorative materials.
It is advisable to seal the exposed dentin surface with a non
irritating, insulating substance.
 The rapid penetration and spread of caries in dentin is the result
of tubule system in dentin. The dentinal tubules provide a
passage for invading bacteria and their products through either
their thin or thick dentinal layer.
 The sensitivity of the dentin has been explained by the
hydrodynamic theory, that alteration of the fluid and cellular
contents of the dentinal tubules causes stimulation of the nerve
endings in contact with these cells

98. 98
• The basic principle of treatment of
hypersensitivity are to block the
patent tubules or to modify or block
the pulpal nerve response.
• The most inexpensive and first line
treatment is to block the patent
tubules with dentrifices containing
potassium nitrate and/or stannous
fluoride.