Dentin is the mineralized hard tissue that forms the bulk of the tooth beneath enamel and cementum. It is sensitive and continues to form throughout life at the expense of the pulp. Dentinogenesis begins when the dental papilla differentiates into odontoblasts. There are three stages of odontoblast development: differentiation, secretory formation of predentin and dentin, and a resting stage. Dentin is composed of hydroxyapatite crystals embedded in a collagen matrix. It has tubules that house odontoblast processes and dentinal fluid. The structure and composition of dentin provides strength and protection for the pulp.

1. Dentin

2. Definition:
Dentin is the mineralizedDentin is the mineralized hard tissue forminghard tissue forming
the main bulk of the tooth. Covered by enamelthe main bulk of the tooth. Covered by enamel
in the crown and cementum in the root.in the crown and cementum in the root.
2 major properties distinguishes D from E. 12 major properties distinguishes D from E. 1stst
D is sensitive, 2D is sensitive, 2ndnd
D is formed throughout lifeD is formed throughout life
at the expense of pulp.at the expense of pulp.

4. Formation of dentin begins
when the tooth germ reach the
bell stage. The dental papilla is
the formative organ of dentin,
separated from the inner dental
epithelium by cell free zone.
Dentin is formed by cells called
odontoblasts that differentiate
from ectomesenchymal cells of
the dental papilla following an
induction coming from the
inner dental epithelium.
Dentinogenesis

5. A good blood supply and alkaline
phosphatase E are required thus, the
dental papilla is the formative organ of
dentin and it becomes the pulp of the
tooth, a change in terminology generally
associated with the moment of dentin
formation beginning.
As differentiation progresses, the cells
grow in length, the acellular zone
gradually disappeared and reaches
about 40 µ in height and 7 µ in width.
The newly differentiated cells are
characterized by their nuclei positioned
away from inner dental epithelium.
Unlike amelogenesis which has a well
defined end point, dentinogenesis will
continue throughout life of the tooth.

6. 1. Odontoblast Differentiation (Pre-odontoblasts).
2. Formative (secretory) stage:
a. Mantle dentin formation.
b. Odontoblastic process appearance.
3. Quiescent (resting) stage.
Life cycle of odontoblasts

7. The
late
bell
stage

9. 1. Odontoblast differentiation:

10. 1. Odontoblast differentiation:

11. 2. Formative stage:

12. 2. Formative stage (Mantle dentin formation beginning):
secretory odontoblasts are aligned
along the periphery of the pulp.
Functionally, this cell is considered to
consists of 2 distinct parts: cell body in
which synthesis and secretion of
proteins occurs and cell process
whereby secretion occur. The
odontoblastic process consists of one
main bulk with numerous lateral
branches along its length. The first sign
of dentin formation is the appearance
of distinct, large-diameter collagen
fibrils called Von Kroff’s fibersVon Kroff’s fibers.

13. These fibers consist of collagen type III. They
originate deep among the odontoblasts, extend
toward the inner dental epithelium, and
immediately below the epithelium.

14. 2. Formative stage (Odontoblastic process formation):

17. 3. Resting stage:
This stage occurs after
completion of the circumpulpal
dentin. The odontoblast cell
loses most of their protein
forming organelles to
accommodate the decrease in
their function.

18. The fully differentiated and
actively secreting odontoblasts
decrease slightly in size and the
cell process stop to elongate as
dentin formation is reduced.
Meanwhile the odontoblasts had
reached the quiescent stage,
however, they produce dentin in a
very slow rate but may be
reactivated after injury.

19. Dentinogenesis
Matrix formation
(predentin formation)
Mineralization
Predentin maturation

20. 1. Formation of predentin (dentin1. Formation of predentin (dentin
matrix formation):matrix formation):

21. •Formation of circumpulpal dentin:
Once the layer of mantle dentin is formed, dentinogenesis
continue in a slightly different manner to form circumpulpal
dentin which is the basic structure of dentin and forms its bulk.
The odontoblasts increase in size obliterating the intercellular
spaces with extensive junctional complexes develops to form
distinct row of odontoblasts.
As the matrix is formed, the odontoblasts begin to move towards
the pulp. The plasma membrane of the odontoblasts adjacent to
the inner dental epithelium pushes out several short processes
called Odontoblastic Process (Tom’s Fiber).
Occasionally, one of them may penetrate the basement
membrane and interpose itself between the cells of the inner
dental epithelium to form Enamel Spindle.

22. Circumpulpal dentin is formed in a similar way to
mantle but differ from mantle dentin in:
•The collagen fibers are smaller in diameter 0.05 µm
and more closely packed and interwoven with each
other.
•The fibers are generally present at right or oblique
angle to the tubules (parallel to dentin surface).
•The ground substance is exclusively a product of
odontoblasts.

23. 2. Maturation (mineralization) of predenitn:2. Maturation (mineralization) of predenitn:

24. Once the first crystal forms within
such vesicle it grows rapidly and
rupture through the vesicle wall to
spread as a cluster of crystallites and
fuse with adjacent clusters to form a
fully mineralized matrix. Apetite
crystals will obsecure the collagen
fibrils of the dentin matrix. However,
when these globules do not fuse with
each other, areas of uncalcified dentin
are left and known interglobular
dentin. The predentin is then
calcified in a linear pattern or
occasionally by globular pattern.

25. Mineralization sequence
of matrix appears
primary by crystal
deposition in the form of
fine plates of hydroxy-
apatite on the surface of
collagen fibrils and the
ground substance.

26. The long axis of crystals are
paralleling the fibril axis in
rows. Occasionally, the
crystals appear to be
deposited in the fibrils
themselves.

27. The dentin mineralization follows two different
patterns, linear and globular depending on the
rate of dentin formation:
*Globular calcification: deposition of crystals in
several areas of the matrix at one time, with
continued calcification, globular masses
develops, which enlarge and fuse to form a
single mass, usually present in mantel dentin
where matrix vesicle give rise to mineralization
fossi that grow and coalesce. The size of
globules depends on the rate of dentin
deposition with the largest globules occurs when
dentin deposition is fast. When it slow down the
mineralization front appears uniform and
mineralization is linear.
* In circumpulpal dentin , mineralization front
can progress in a linear or globular pattern.

28. Dentin

29. 1.The physical and chemical
properties of dentin.
2.The histological structure and
ultrastructure of dentin
3. Age changes and clinical
consideration.

30. Dentin is primarily formed from
secretory products of the odontoblast
and their processes. It is the hard
tissue that constitute the body of each
tooth serving as both a protective
covering of the pulp and as support for
the overlying enamel. Unlike enamel,
dentin is a vital tissue containing the
cell processes of odontoblasts.

31. Physical properties

32. • Colour
• Hardness
• Brittleness
• Permeability
• Thickness
• Radiograph

33. Chemical properties

34. Inorganic
65-70%
Organic
30-35%

35. Mature dentin composed of approximately: 70% inorganic
material, 20% organic material, 10% water by weight.
•Inorganic component: consists mainly of calcium
hydroxyapatite crystals. The crystals are plate like-shape,
appear needle shape in edge view.
Crystals are 0.05-0.06 µm in length and may reach up to
0.1µm.
•Organic component: consists of fibrils embedded in an
amorphous ground substance. The fibrils are collagen over
90% of the organic content, small inclusion of non-
collagenous protein matrix

36. Classification of dentin
According to the sequence of formation, dentine
classified as:
•Primary dentin.
•Secondry dentin.
•Tertiary dentin.

37. Primary dentin
It is the dentin formed before complete
root formation. Most of the tooth is formed
by primary dentin, which outlines the pulp
chamber and is referred to as
circumpulpal dentin. The outer layer is
called mantel dentin and differs from the
rest of the primary dentin in the way it is
mineralized and its collagen content.

38. Secondary Dentin
It develops after root
formation has been
completed and representing
the continuing but much
slower, deposition of dentin
by odontoblast. The ratio of
mineral to organic material
is the same as for primary
dentin.
The greater deposition of secondary dentin on the roof and floor
of the chamber leads to an asymmetric reduction in its size and
shape. These changes in the pulp space, clinically referred to as
pulp recession.

39. Tertiary Dentin
Tertiary dentin is
reparative, response,
or reactive dentin
this is localized
formation of dentin
on the pulp-dentin
border, formed in
reaction to trauma
such as caries or
restorative
procedures.

41. Histological Structure
I. Odontoblast

42. 1. It is the unit
structure of dentin,
which form a
shallow S shape at
the middle part of
the crown (primary
curvature), and
straight at the
cuspal and root
portions of the
tooth.
2. Over the course
of dentinal tubule,
a regular secondary
curvatures are
seen.
II. Dentinal Tubules

43. Histological Structure
II. Dentinal Tubules with secondary branches

44. Histological Structure
3. The tubules are
packed at their pulp
side and further apart
at the dentinoenamel
junction. This
corresponds to the
small diameter of the
tubule at the
dentinoenamel
junction and the
longer diameter at its
pulpal end.
II. Dentinal Tubules

45. Histological Structure
II. Dentinal Tubules

46. The primary curvature result from crowdingThe primary curvature result from crowding
and the path followed by the odontoblasts asand the path followed by the odontoblasts as
they move toward the center of the pulp.they move toward the center of the pulp.
2ndary curvature due to changes in direction of2ndary curvature due to changes in direction of
much smaller amplitude which result in a spiralmuch smaller amplitude which result in a spiral
track taken by the odontoblast during its coursetrack taken by the odontoblast during its course
from the outer dentin surface to the pulpfrom the outer dentin surface to the pulp

47. Tubules taper from 2.5 um in diameter near the pulp to 1.2Tubules taper from 2.5 um in diameter near the pulp to 1.2
um in the midportion of dentin and 900 nm near the ADJ.um in the midportion of dentin and 900 nm near the ADJ.
No of tubules differ according to tooth age and thicknessNo of tubules differ according to tooth age and thickness
of dentin 30000/mm2 in outer dentin, 40000 in the middle,of dentin 30000/mm2 in outer dentin, 40000 in the middle,
and 760000 in inner dentin. ( the ratio between no ofand 760000 in inner dentin. ( the ratio between no of
tubules/unit area on the pulpal and outer surface is 4:1tubules/unit area on the pulpal and outer surface is 4:1

48. Contents of dentinal tubulesContents of dentinal tubules
Contain od process, afferent nerve terminals,Contain od process, afferent nerve terminals,
extracellular fluid called dentinal fluid orextracellular fluid called dentinal fluid or
dental lymph. If dentin is fractured , fluiddental lymph. If dentin is fractured , fluid
exudates emit from tubules and form dropletsexudates emit from tubules and form droplets
on the surface of dentin. This suggest aon the surface of dentin. This suggest a
pressure force from pulpal tissue outwards thatpressure force from pulpal tissue outwards that
help to limit the progress of chemicals andhelp to limit the progress of chemicals and
toxins toward the pulp. The tissue changes intoxins toward the pulp. The tissue changes in
dentin occurs through this fluid.dentin occurs through this fluid.

49. Histological Structure
1. It is the cytoplasmic process of the odontoblast that
run inside the dentinal tubule.
III. Odontoblastic process

51. Histological Structure
2. It undergoes
several branches at its
terminal end while
along its course it
sends out several
lateral branches
enclosed in the
canaliculi. These
lateral branches fuse
with the lateral
branches of the
adjacent
odontoblastic
processes.
III. Odontoblastic process

52. Histological Structure
3. While the odontoblastic processes usually end at the
dentinoenamel junction, some processes traverse this junction to a
short distance in the space of enamel and are known as enamel
spindle.
III. Odontoblastic process

53. Od process structureOd process structure
differ according to thediffer according to the
site in dentin . Nearsite in dentin . Near
pulp, it contains morepulp, it contains more
organelles, away isorganelles, away is
little organelleslittle organelles

57. Histological Structure
In cross section the wall of the dentinal tubule is seen surrounding
the odontoblastic process, while the dentin is found also external to
the dentinal tubules. The wall of dentinal tubule forms the
peritubular dentin. It is more highly mineralized than inter tubular
dentin ( 40% excess). Can be distinguished from intertubular by by
increase radio-opacity
IV. Peritubular dentin

58. Histological Structure
The dentin found between the dentinal tubules is the intertubular
dentin. It contains less than one half of its volume an organic matrix,
which consists of collagen fibrils dispersed in ground substances.
V. Intertubular dentin

59. The width of peritubular dentin atThe width of peritubular dentin at
the pulpal end is .04 um and .75the pulpal end is .04 um and .75
um at ADJ. if external stimulusum at ADJ. if external stimulus
occurs. It result in acceleration inoccurs. It result in acceleration in
per T D formation. If the stimulusper T D formation. If the stimulus
is severe, marked reduction in DTis severe, marked reduction in DT
occurs till obliteration.occurs till obliteration.
In cross section, peri T D appearIn cross section, peri T D appear
as translucent rings . It wasas translucent rings . It was
thought that the sharp boundry ofthought that the sharp boundry of
this ring due to a special structurethis ring due to a special structure
called Neumann sheath but EMcalled Neumann sheath but EM
failed to prove it as it was shownfailed to prove it as it was shown
the organic fibrils of thethe organic fibrils of the
peritubular D continuous with thatperitubular D continuous with that
of inter tubular D.of inter tubular D.

62. Histological Structure
I. Incremental lines:
A. Incremental lines of Von Ebner.
VI. Hypocalcified structures:
B. Contour lines of Owen.
C. Neonatal line.
II. Interglobular dentin.
III. Granular layer of Tomes.

63. Histological Structure
II. Interglobular dentin:

64. Histological Structure
II. Interglobular dentin:
Because this irregularity of dentin is a defect of mineralization and
not of matrix formation, the normal architectural pattern of the
tubules remains unchanged, and they run uninterrupted through the
interglobular areas. However, no peritubular dentin exists where the
tubules pass through the mineralized areas.

65. Histological Structure
This layer can be seen
just below the surface of
the dentin where the root
is covered by cementum.
It occurs from the
cementoenamel junction
to the apex of the tooth.
It is only found in root
dentin and does not
follow the incremental
lines
III. Granular layer of Tomes.

66. Histological Structure
Theories of granular layer of
Tomes occurrence:
III. Granular layer of Tomes.
1. It may be due to interference with
the mineralization of the firstly
formed layer of dentin.
2. They may represent smaller areas
of interglobular dentin than that found
in the crown.
3. Looping of the terminal ends of the
tubules due to different orientation of
odontoblast processes during initial
dentin formation.
4- B.V

67. Age changes (Repair & Defence Mechanisms)
I. Physiologic secondry dentin:
This type of dentin is formed after complete root formation, and is
deposited continously as long as the pulp is vital. However, it is
formed at a lower rate and is separated by darkly stained line from
the primary dentin.

68. Repair & Defence Mechanisms
I. Physiologic secondry dentin:
Near to this line, the
tubule bend more or
less sharply, and
their course shows
varying degrees of
irregularities. It
shows less number
of tubules/unit area
than in primary
dentin, and usually
is deposited with
higher rate at the
roof and floor of the
pulp chamber.

69. Repair & Defence Mechanisms
I. Physiologic secondry dentin:
These changes in the structure and
arrangement of dentinal tubules
may be related to the progressive
crowding of odontoblasts which
ends by the loss of some and
rearrangement of the remaining
ones.
Q: why these changes occur between primary and secondary
dentin?

70. II. Irregular secondary dentin (reparative):
This results from attrition, caries and operative cutting
procedures.
It takes many names such as osteodentin, atubular dentin

71. Repair & Defence Mechanisms
II. Pathologic secondry dentin:
B. Reparative dentin:
Under the previously mentioned conditions that lead to the formation of the
pathological type of dentin, the corresponding odontoblast to the injured area of
dentin will be more or less damaged. If the odontoblasts are less damaged they
will be stimulated to continue dentin formation.

72. Repair & Defence Mechanisms
II. Pathologic secondry dentin:
B. Reparative dentin:
In case of severly damaged odontoblasts, they are replaced by the underlying
undifferentiated mesenchymal cells found in the subodontoblastic layer. Damaged
or newly differentiated odontoblast are stimulated to deposit reparative dentin to
seal off the injured area of dentin.

73. Repair & Defence Mechanisms
II. Pathologic secondry dentin:
B. Reparative dentin:
General characteristics of reparative dentin:
1. The course of the dentinal tubules is twisted.
2. The number of the dentinal tubule is greatly decreased.
3. Odontoblasts are frequently included within the forming reparative dentin
(osteodentin).
4. Reparative dentin is separated from other dentin by deeply stained line.
5. Some areas in reparative dentin does not contain dentinal tubules
( atubular dentine ).

74. Repair & Defence Mechanisms
II. Pathologic secondry dentin:
C. Sclerotic dentin ( transparent dentin ):
In addition to the formation of
reparative dentin as a result of
injurious stimuli, changes also occur
in the surrounding and damaged
dentin. This is seen through the
deposition of calcium salts in or
around the degenerated odontoblastic
process.

75. Repair & Defence Mechanisms
III: Dead tract :
Odontoblastic processes may disintegrate by any injrious stimuli, most oftenly in
areas of narrow pulp horn due to odontoblasts crowding. In ground section these
dentinal tubules appear black where they are empty. Dentinal tubules with
degenerated odontoblastic processes are called dead tracts.

76. Dentine sensitivity
The only type of sensation obtained
in dentine pulp complex is pain.
There are three basic theories of
pain conduction through dentin.

77. Dentine sensitivity
I. The direct neural stimulation:

78. Dentine sensitivity
The nerve fibers arise from the
plexus of Raschkow, enter the
predentin, and return to region
the plexus again.
I. The direct neural stimulation:

79. Dentine sensitivity
The controversy:
I. The direct neural stimulation:

80. Dentine sensitivity
This theory considers the odontoblast to be a
receptor cell. This was argued that because the
odontoblast is of neural crest origin, it retains an
ability to transduce and propagate an impulse.
2. Transduction theory

81. Dentine sensitivity
The controversy:
2. Transduction theory

82. Dentine sensitivity
2. Hydrodynamic theory:

83. Dentine sensitivity
The agreements:
2. Hydrodynamic theory

84. Clinical considerations