Dentinogenesis & histology of dentin

For my dental students

1. Dentinogenesis & Histology
Of Dentin
Dr/ HeshamDameer

2. 1.Dentinogenesis
2.Physical properties of dentin
3.Chemical composition
4.Dentin structure
5.Types of dentin
6.Age changes of dentin
7.Innervation of dentin
8.Theories of pain transmission through dentin

3. Dentinogenesis is a two-phase sequence
in that:
Dentin matrix
formation (predentin)
which is the elaboration
of uncalcifiedorganic
matrix
Mineralization,
which does not begin
until a fairly wide
band of predentinis
formed.
Collagen fibers
Ground
substance
Hydroxyapatite
crystals
1
2

4. Primary physiologicdentin formation
•Mantle dentin
•Circumpulpal dentin
Primary physiologic dentin is the dentin formed
prior to root completion, it is formed of :

5. Odontoblastsdifferentiation
1.Dentin is formed by odontoblast cells that
differentiate from ectomesenchymalcells ( EMC )
of dental papilla following an organizing influence
of the inner enamel epithelium.
2.Odontoblast differentiation occur in the preexisting
ground substance of the dental papilla

6. 3-EMCof DP undergo a number of cell divisions, in the
final division the mitotic spindles (B) are perpendicular to
the basement membrane supporting the inner E epithelium,
so it gives 2 daughter cells superimposed, the
odontoblasts(C) and the subodontoblasticlayer (F).

7. Odontoblastdifferentiation. The undifferentiated ectomesenchymalcell(A)of the
dental papilla divides(B),with its mitotic spindle perpendicular to the basal
lamina(pink line). A daughter cell(C),influenced by the epithelial cells and
molecules they produce(D),differentiates into an odontoblast(F). Another
daughter cell(E),not exposed to this epithelial influence, persists as a
subodontoblastcell(G). This cell has been exposed to all the determinants
necessary for odontoblastformation except the last .

8. Differentiation of odontoblasts.
Differentiate from
the peripheral
dental papilla cells
(UMC)
At first become
short columnar cell
with many stubby (
short & thick )
processes
Preameloblasts
Basement
membrane
The cells grow in length
(40u) and closely packed
together
Ameloblasts

9. Primary Dentin formation

10. Matrix formation
Forming the bulk of the tooth
dentin .Comprises intertubular
and peritubular dentin Small-
diametercollagen fibrils
parallel to basal lamina .
*Ground substance formed
exclusively by odontoblasts
Glycoprotiens, proteoglycans
and lipids .
Formation of peritubular dentin .
*large-diametercollagen fibrils
perpendicular to basal
lamina(von Korff’s fibers) .
Source: from
Preexisting ground substance
of dental papilla
Glycoprotiens, proteoglycans
Mantle dentin Circumpulpal dentin

12. Odontoblastcells at first have many short
processes, as the odontoblastmoves away
toward the center of the pulp, one of its short
processes becomes accentuatedand left behind
to form the principal extension of the cell, the
odontoblastprocess or Tomes’ fiber

13. Odontoblasticprocess formation
At first more than one process
As more D is laid down, the cells receed
and leave single process ( Tomes’ fiber)

15. Changes in the dental papilla associated with initiation of dentin formation.A,An acellular
zone(*)separates the undifferentiated cells of the dental papilla (preodontoblasts,pOd)
from the differentiating inner enamel epithelium (ameloblasts,Am).BtoD,Preodontoblasts
develop into tall and polarized odontoblasts(Od)with the nucleus away from the matrix they
deposit at the interface with ameloblasts. The matrix first accumulates as an unmineralized
layer, predentin(PD),which gradually mineralizes to form mantle
dentin(D).Odp,Odontoblast process;SI,stratum intermedium;SR,stellate reticulum.

16. A,The odontoblastprocess(Odp)is the portion of the cell that extends above the cell web(cw). Numerous typical,
elongated secretory granules(sg),occasional multivesicularbodies(mvb),and microfilaments(mf)are found in the
process. The small collagen fibrils(Coll)making the bulk of predentinrun perpendicularly to the processes and
therefore appear as dotlikestructures in a plane passing longitudinally along odontoblasts. Bundles of larger-diameter
collagen fibrils, von Korff’sfibers, run parallel to the odontoblastprocesses and extend deep between the cell
bodies.B,At higher magnification, a von Korff’sfiber extending between two odontoblastsshows the typical fibrillar
collagen periodicity.m,Mitochondria;rER,rough endoplasmic reticulum.
Transmission EM image
Korff’s fiber between 2 odontoblasts

17. Mineralization
The hydroxyapititecrystals first
appear in matrix vesicles(in the
cytoplasm of odontoblasts) as
single crystals that grow rapidly
fuse with the cell membrane and
ruptureto spread as cluster of
crystallites that fuse with
adjacent clusters to form a
continuous layer of mineralized
matrix.
Mantle dentin
( Matrix vesicles are generated by odontoblasts )

18. Dentinogenesis requires a good blood supply, during mantle
dentin formation blood capillaries are found in the
subodontoblasticlayer. As circumpulpaldentinogenesisis
initiated these capillaries migrate between the odontoblasts.
No matrix vesicles are
generated by odontoblasts and mineralization
involves heterogeneous nucleation .
With continued crystal growth, globular masses are
formed, that continue to enlarge and fuse to form a
single calcified mass.
Circumpulpal dentin

19. 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
junctionalcomplex

20. 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 remaining
circumpulpal dentin (no M V ).
Crown
Root

21. Matrix formation Mineralization

22. Pattern of mineralization
1.Globular calcification.
2.Linear calcification.
Depend on the rate of dentin formation

23. Globular mineralization
Involves the deposition of crystals in several discrete
areas of matrix ,with continuous growthglobular
masses are formed that continue to enlarge and then
fuse to form single calcified mass, this pattern is best
seen in mantle dentin.
In circumpulpaldentin the mineralization front may be
globular or linear.

24. Globular mineralization

25. Globular mineralization

26. Linear mineralization
The type of mineralization depends on the rate
of dentin formation, the largest globules
occurring where dentin deposited faster.
When the rate of formationprogress slowly, the
mineralization front appears more uniform
and linear.

27. Linear mineralization

28. Dentin Structure

29. Physical Properties
1.Light yellowish in color.
2.Slightlycompressible and highly
elastic.
3.Harder than bone andsofter than
enamel.
4.Moreradiolucent(in X-ray)than
enamel.
5.Moreradiopaquethan cementum
or bone.

30. Chemical Composition
1.Organic matter (collagen fibrils and a ground
substance) 20% and water 10%
2.Inorganic materials 70% : hydroxyapatitecrystals
3Ca3(PO4)2.Ca(OH)2
Organic and Inorganic substances can be separated
by decalcificationor incineration.

31. Dentin Structure
1.Dentinal tubules.
2.Odontoblasticprocesses.
3.Peritubulardentin.
4.Intertubulardentin.
5.Predentin.

32. L.S. showing pulp, dentin, PDL, and bone . H&E stain
DP PDL
B

33. 1. Dentinal Tubules
*In the crown, DT follow a gentle curve (S-
shaped)except under the incisaledges and cusp
tips(straight)
*Start at right angle from pulpalsurface, the
first convexity toward the root apex.
*In the root, their course are almost straight.

34. LGSsection showing the course
of dentinal tubules

35. Dentinal Tubules
Coronal dentin
Root dentin
By Hesham Dameer

36. *The ratio between the surface areas at the
outsideandinside of the dentin is5:1.
*Accordingly, the tubules are further apart in
the peripheral layer and are closely packed near
the pulp.

37. Dentinal tubules –A: near DEJ, B: near the pulp (EM X3.000)
A B

38. *DT exhibit secondary curvature over their
entire length.
*Have lateral branches (canaliculi), 1 um in
diameter, at right angle to the tubule.
*Have terminal branches –more in root dentin
than in coronal dentin.

39. Terminal branching of dentinal tubules

40. Dentinal tubules

41. Canaliculiin the dentinal tubules. SEM X 15.000

43. 2. OdontoblasticProcesses (Tome’s fibers)
*Are cytoplasmic extensions of the odontoblasts
occupying the DT .
*They are thicker near the cell body, 3-
4micrometer, and taper to 1mic. further into the D.
*They divided near their terminal ends into
several terminal branches.
*They send out thin 2ry processes enclosed in
fine tubules to unite with neighboring ones.

44. Dentinal tubule(A) –Odontoblasticprocess(B)

45. SEM
TEM
OPD: Odontoblast processes, Arrowheads: Dentinal
tubules

46. Lateral communication between dentinal tubules.
Note terminal branches

47. Lateral communication between dentinal tubules

48. *Some terminal branches extend into the enamel
as enamel spindle.
*Others may remain short in dentinal tubules.
*Occasionally a process splits into 2 equally thick
branches.

49. LGS showing enamel spindle

50. The cytoplasmic contents include:
1.Microtubulesof 200-250 A
0
in diameter.
2.Filamentof 50-75 A
0
diameter.
3.Occasional mitochondria.
4.Some dense bodies resembling lysosomes.
5.Coated vesicles.
6.Microvesicles.
Note: (absence of ribosomes and endoplasmic reticulum).

51. 3. PeritubularDentin
*Best seen in cross sections
*It forms a ring shaped transparent zone surrounding
the odontoblasticprocess forms the wall of the DT.
*Peritubular D is more mineralized (9%) than the
Intertubular dentin.

52. Peritubular(A), Intertubular dentin(B) and
Odontoblast process space(C)

53. Dentinal tubules
Peritubular dentin Intertubular dentin

54. 4. Intertubular Dentin
Forms the main body of Dentin, located between the DT.
½ of its volume is organic matrix (fibrils and ground substance).
Collagen fibrils are randomly oriented around the DT .
They run parallel to D surface, at right angles to the tubules.
Hydroxyapatite crystals(1um length) are formed parallel to the
Collagen F. .

55. Near the pulp –random arrangement of calcifying collagen
fibers surrounding dentinal tubules. SEM X 15.000

56. Collagen fibers composing the walls of dentinal tubules

57. Canaliculi(white arrow) –peritubular dentin(black arrow)

58. 5. Predentin
Is thefirst formed dentin (not mineralized).
Located adjacent to the pulp tissue.
Width: 2-6 um.
Mineralized to become Dentinand new layer of
predentin forms circumpulpally.

59. C
A: Dentin B: Predentin

60. P
D
O
D
p
A: Dentin B: Predentin, O: Odontoblasts

61. Types of Dentin

62. 1. Primary physiologicDentin
(Mantle and Circumpulpal)
*The first formed layer beneath enamel and
cementumis known as mantle D. Mantle dentin is
about 20 um thick.
*It contains coarse fibril bundles (Korff’sfibers)
arranged at right angles to the D surface.

63. *The remaining portion of dentin that forms the main
bulk of the tooth is known as circumpulpaldentin.
*It is more mineralized than mantle D.
*Collagen fibrils are fine and closely packed together.
*It represents all dentin formed prior to root completion

64. 2. Secondary physiologicDentin
*Formed under normal condition and may continue
throughout life.
*Formed after root completion.
*It is separated from 1primary Dentin by dark stained
line, the Dentinal Tubules bend sharply at this line.

65. *In 2ry D the D T are comparable to those of 1ry D
both in regular arrangement &in numbers
*It is deposited more in the floor and roof of the
pulpal chamber than on the side walls.
*It is deposited also at the pulp horns, reducing their
hight.

66. SD
PD
GS showing the sharp bend between primary PD & secondary dentin SD

67. D S : showing primary & secondary dentin

68. 3.ReparativeDentin
*Noxious stimuli (Attrition, erosion, abrasion, cariesor
operative procedures) may exposeor cut the
odontoblast processes.
*The entire cell may severely damaged and continueto
form reparative D or degeneratesand replaced by
undifferentiated pulpalcells.

69. *Reparative (tertiary) dentin seals offthe area of
injury ( defense mechanism of the pulp) so, it is
localized to the site of the stimulus.
*Here the tubules are twisted and reducedin number.

70. *Reparative D is separated from
1ryor 2ryD by a deeply
stained line.
*Some D forming cells may be
included( entrapped) inrapidly
produced matrix forming
(osteodentin).

71. Types of Dentin

72. Pulp healing –dentin bridge with normal pulp

73. 4. InterglobularDentin
*It is the unmineralizedor hypomineralizedregions located
between the unfusedmineralized globules of cacification.
*It is observed in the circumpulpaldentin just below the mantle
dentin.
*The DT pass uninterrupted through the uncalcified areas of IGD.
*IGDfollow the incremental pattern of the tooth.
*In ground section the IGDislost, replaced by airand the spaces
appear black.

74. SEM showing Globular dentin

75. Decalcified H & E stained section showing A: Globular dentin
B: Predentin

76. Interglobular Dentin
Inter-
globuler
dentin
Dentinal
Tubules
Dentino
Enamel
Junction

77. Interglobulardentin in decalcified & ground sections

78. 5. Tome’s GranularLayer
*Seen in the ground section adjacent to cementum(CDJ).
*Made of minute areas of IGD.
*It does not follow the incremental pattern.
*It represents an interference with mineralization of surface layer
of root dentin beforecementumformation.
*It may result from thelooping and coalescingof the terminal
branches of the DTas a result of the odontoblaststurning on
themselvesduring early stages of root D formation (recent
evidence).

79. Ground LS showing Tome’s granular layer

80. Dentin
Cementum
Granular layer
of Tomes
By Hesham Dameer

81. 6. Transparent (Sclerotic) Dentin
*Stimuli may lead to deposition of Ca salts (apatite
crystals) inor arounddegenerating odontoblasticprocess
(defense mechanism of Dentin).
It Can be observed:
1. In roots of elderly teeth.
2. Around the dentinal part of type B enamel lamellae.

82. Ground LS showing Enamel caries and sclerotic dentin
(dye-filled dentinal tubules)

83. 3. Under slowly progressing caries.
4. It is harder than normal dentin.
5. Seen only in ground sections.
6. Appears light in transmitted and dark in reflected
light.

84. 7. Dead Tracts
*Seen in ground sections of normal dentin.
*Odontoblasticprocesses disintegrate ( due to caries, attrition,
cavity prep., etc…) and empty tubules filled with air appear.
*Appear black in transmitted light and white in reflected
light.
*Reparative D sealsthese tubules at their pulpal end.
*These areasdemonstrate decreased sensitivity.

85. Dead tract
Ground LS showing Reparative dentin

86. Age and Functional Changes
1.Vitality of dentin.
2.Attrition.
3.Permeability.
4.Secondary dentin.
5.Reparative dentin.
6.Dead tract.
7.Sclerotic dentin.

87. Incremental Lines of dentin
1.Daily Incremental lines
2.Incremental lines of Von Ebner.
3.Contour lines of Owen( hypocalcified
bands).
4.Neonatalline.

88. 2.Incremental lines of von Ebner
*Run at right angles to DT
*Reflect the daily rhythmic deposition of
dentin matrix(4-8 Um)
1.Daily Incremental lines
* 5-dayrhythmic pattern of dentin
deposition (20 Um interval)

89. Incremental lines of Von Ebner

90. 3.Contour lines of Owen
Contour lines are accentuated incremental lines result from
disturbances in mineralization process ( periods of illnessor
inadequate nutrition)
Soft x-ray analysis showed these lines as hypocalcified bands.
4. Neonatalline
1.In deciduous teeth and in the first permanent molar, accentuated
incremental line separates between prenatal and post natal
dentin.
2.It reflects the abrupt change in environment that occurs at birth.
3.It may be a zone of hypocalcification.

91. Contour line of Owen(arrowed)

92. Vitality of D:
*Dentin is a vital tissue since the odontoblasts and their
processes are an integral part of it.
*Vitality is the capacity of the tissue to react to
physiologic and pathologic stimuli
*Pathologic effects of caries, abrasion, attritionor
operative procedures cause changes in D

93. Innervation of Dentin
*Dentin is sensitiveto any kind of stimuli.
*Silver impregnation is not specific to demonstrate nerve
fibers.
*DT contain numerous nerve endings in the predentinand
inner dentin (100-150 um) in close association with the
odontoblasticprocesses within the tubules.

94. *Nerve endings are numerousin the pulp horns.
*Nerve endings are packed with small vesicles containing
neurotransmitter substances.Most of these endings are
terminal processes of the myelinatednerve fibers.
*The primary afferent somatosensory nerves of the dentin
and pulp project to main sensory nucleus of the
midbrain.

95. Theories of pain transmission
through Dentin

96. A: Direct conduction Theory
B: Transduction Theory
C: Hydrodynamic Theory
A B C

98. 1. Direct Conduction Theory:
*In which stimuliin some manner as yet unknown,
directly reach the nerve endings in the inner dentin
in the tubules.
*There is little scientific support of this theory.

99. 2. Transduction Theory:
*In which the membrane of the odontoblastic process is
the primary structure excited by the stimulus and that
the impulse is conductedor transmittedto the nerve
endings in the predentin, odontoblast zone, and pulp.
*This is not a popular theory since there are no
neurotransmitter vesicles in the odontoblastic process to
facilitate the synapse.

100. 3. Hydrodynamic Theory
*In which various stimuli such asheat, cold, air blast
desiccation, mechanical or osmotic pressure affect fluid
movement in the DT
*This fluid movement, either inward or outward, stimulates
the pain mechanism in the tubules bymechanical
disturbance of the nerves endings closely associated with
the odontoblast and its process.
*Thus these endings may act as mechanoreceptorsas they
are affected bymechanical displacement of the tubular
fluid.

101. •Ten Cate’s AR (Oral Histology ,development ,
structure and function ) 8
th
edition, Antonio
nanci. Elsevier Health Sciences, 2008.
•Orban’s Oral Histology and Embryology, 13
th
edition, G S Kumar. Elsevier India, 2011.