3. Dr. Nithin Mathew - Dentin
Incremental lines
Odontoblastic processes
Properties
Physical
Chemical
Innevervation of dentin
Theories of pain transmission
Direct neural stimulation theory
Transduction theory
Hydrodynamic theory 3
4. Dr. Nithin Mathew - Dentin
Age & functional changes
Vitality of dentin
Dead tracts
Sclerotic dentin/ transparent dentin
Clinical considerations
Conclusion
References
4
5. Dr. Nithin Mathew - Dentin
INTRODUCTION
Second layer of the tooth
Structure that provides the bulk and general form of
the tooth
Since it begins to form slightly before the enamel, it
determines the shape of the crown, including the cusps
and ridges and also the number and size of the roots.
5
6. Dr. Nithin Mathew - Dentin
Physically and chemically, it closely resembles bone
Said to be a living tissue since the tubules present in it
contains processes of specialised cells, the
odontoblasts.
Main morphologic difference between bone and dentin
is that some of the osteoblasts exists on the surface of
the bone and when one of the cells becomes enclosed
within its matrix, it is called an osteocyte.
6
7. Dr. Nithin Mathew - Dentin
But the odontoblasts cell bodies remain external to
dentin, but their processes exist within tubules in
dentin.
7
8. Dr. Nithin Mathew - Dentin
STAGES OF TOOTH DEVELOPMENT
Teeth develop in distinct stages that are easily
recognizable at the microscopic level.
Hence, stages of tooth development
(odontogenesis) are described by the histologic
appearance of the tooth organ.
The stages are described as the lamina bud,
cap, early bell and late bell stages of tooth
development. 8
9. Dr. Nithin Mathew - Dentin
LAMINA STAGE
First morphologic sign of tooth development
Visible at approximately 6th week of human
development.
At this stage, the cells in the dental epithelium
and the underlying ectomesenchyme are dividing
at different rates, the latter more rapidly.
9
10. Dr. Nithin Mathew - Dentin
The dental lamina has the full potential to induce
tooth formation by dictating the fate of the
underlying ectomesenchyme.
10
11. 11
a : Nasal Septum
b : Tongue
c : Palatal Processes
d : Dental lamina
12. Dr. Nithin Mathew - Dentin
BUD STAGE
The dental lamina continues to grow and thicken to
form a bud
Cells of the ectomesenchyme proliferate and
condense to form the dental papilla.
At this stage, the inductive or tooth forming
potential is transferred from the dental
epithelium to the dental papilla.
12
13. 13
A : Ectodermal outgrowth
B : Dental Mesenchyme
C : Tongue
D : Oral Cavity Space
E : Oral Ecotoderm
14. Dr. Nithin Mathew - Dentin
CAP STAGE
The tooth bud assumes the shape of a cap that is
surrounded by the dental papilla.
Ectodermal compartment of the tooth organ is
referred to as the dental or enamel organ.
The enamel organ and dental papilla become
encapsulated by another layer of ectomesenchymal
cells, called the dental follicle
14
15. Dr. Nithin Mathew - Dentin
Separates the tooth organ
papilla from the other
connective tissues of the
jaws.
Important step in tooth
development, because it
marks the onset of crown
formation.
15
16. 16
a : Outer Dental Epithelium
b : Inner Dental Epithelium
c : Stellate Reticulum
d : Dental Papilla
e : Dental lamina
17. Dr. Nithin Mathew - Dentin
EARLY BELL STAGE
Dental organ assumes the shape of a bell as cells
continue to divide but at differential rates.
A single layer of cuboidal cells called the external or
outer dental epithelium, lines the periphery of the
dental organ
Cells that border the dental papilla and are columnar
in appearance form the internal or inner dental
epithelium.
17
18. Dr. Nithin Mathew - Dentin
The inner epithelium gives rise to the ameloblasts,
cells responsible for enamel formation.
These cells secrete high levels of alkaline phosphatase.
In the region of the apical end of the tooth organ, the
internal and external dental epithelial layers meet at a
junction called the cervical loop.
These extends apically to form the Hertwigs
Epitheial root sheath which forms the root dentin
18
19. Dr. Nithin Mathew - Dentin
Early Bell stage
Each layer of the dental organ has assumed
several functions.
The reciprocal exchange of molecular information
between the dental organ and dental papilla
influences the important events that lead to cell
differentiation at the late bell stage.
19
20. Dr. Nithin Mathew - Dentin
LATE BELL STAGE
The dental lamina that connects
the tooth organ to the oral
epithelium gradually disintegrates
at the late bell stage.
Cells of the internal dental epithelium continue to
divide at different rates to determine the precise shape
of the crown.
Shortly after, cells of the internal dental epithelium at
the sites of the future cuspal tips stop dividing and
assume a columnar shape. 20
21. Dr. Nithin Mathew - Dentin
In summary, development of the tooth rudiment
from the lamina to the late bell stages culminates
in the formation of the tooth crown.
As root formation proceeds, epithelial cells from
the cervical loop proliferate apically and
influence the differentiation of odontoblasts from
the dental papilla as well as cementoblasts from
the follicle mesenchyme.
This leads to the deposition of
root dentin and cementum.
21
22. 22
a : Nerve Bundle
b : Alveolar Bone
c : Vasculature
d : Oral Ectoderm
e : Tongue
24. Dr. Nithin Mathew - Dentin
STRUCTURE OF DENTIN
The dentinal matrix of collagen fibres are arranged in
a network.
As dentin calcifies, the HA crystals mask the collagen
fibres
The bodies of 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 mineralised matrix
24
25. Dr. Nithin Mathew - Dentin
Each cell gives rise to one process which traverses the
predentin & calcified dentin within one tubule and
terminates in a branching network to the DEJ or CDJ
25
26. Dr. Nithin Mathew - Dentin
DENTINAL TUBULES
The course of the dentinal tubules
follow a gentle curve in the crown
where it resembles an S shape
Starts at right angles at the pulpal
surface, the first convexity of this
doubly curved course is directed
towards the apex of the tooth
These tubules end perpendicular to
the DEJ & CDJ
26
27. Dr. Nithin Mathew - Dentin
It is almost straight near the root tip and along the
incisal edges and cusps
Dentin thickness ranges from 3-10mm or more
Ratio btwn outer and inner surfaces of dentine is about
5:1
No. of tubules per square millimeter varies from 15000
at the DEJ to 65000 at the pulp – density and
diameter increases with depth
27
28. Dr. Nithin Mathew - Dentin
There are more tubules per unit area in the crown
than in the root
These dentinal tubules have
lateral branches throughout dentin,
which are termed canaliculi or
microtubules
A few odontoblastic processes
extend through the DEJ into
the enamel several millimetres.
These are called
Enamel Spindles 28
31. Dr. Nithin Mathew - Dentin
PERITUBULAR DENTIN
The dentin that immediately surrounds
the dentinal tubules is termed
peritubular dentin
Highly mineralised than intertubular dentin
Twice as thick in outer dentin(approx. 0.75µm) than
inner dentin(approx. 0.4µm)
Calcified tubule wall has an inner organic lining
termed the Lamina Limitans which is high in
glucosaminoglycans (GAG)
31
32. Dr. Nithin Mathew - Dentin
INTERTUBULAR DENTIN
Located btwn the dentinal tubules or more
specifically btwn the zones of
peritubular dentin
One half of its volume is
organic matrix, specifically collagen fibres
The fibrils range from 0.5-0.2µm in diameter and
exhibit crossbanding at 64µm intervals
HA crystals are formed along the fibres with
their long axis oriented parallel to the collagen
fibres
32
33. Dr. Nithin Mathew - Dentin
Well mineralised
Provide tensile strength to dentin
33
35. Dr. Nithin Mathew - Dentin
PREDENTIN
Located adjacent to the pulp tissues
2-6µm, depending on the activity of odontoblasts
First formed dentin and is not mineralised
The collagen fibres undergo mineralization at the
predentin – dentin front, the predentin then
becomes dentin and a new layer of predentin
forms circumpulpally 35
37. Dr. Nithin Mathew - Dentin
ODONTOBLASTIC PROCESSES
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
7µm in diameter & 40µm in length
37
40. Dr. Nithin Mathew - Dentin
PRIMARY DENTIN
Dentin that is formed prior to
eruption of a tooth.
Classified as Orthodentin, the
tubular form of dentin lacking
of cells found in teeth of all
dentate mammals
Secreted at a relatively higher
rate
Constitutes major part of the
dentin in the tooth 40
41. Dr. Nithin Mathew - Dentin
PRIMARY DENTIN
Mantle dentin is the first
formed dentin in the crown
underlying the DEJ
Regular in structure
Dentinal tubules form S-shape
as a result of directional
movement of odontoblasts
It is the outer or most
peripheral part of the primary
dentin and is about 150µm thick 41
42. Dr. Nithin Mathew - Dentin
Circumpupal dentin forms the remaining
primary dentin or the bulk of the tooth
The fibrils are much smaller in diameter and are
more closely packed together
Slightly more mineral content than in mantle
dentin
42
43. Dr. Nithin Mathew - Dentin
SECONDARY DENTIN
Formed after root completion
Narrow band of dentin
bordering the pulp
Contains fewer tubules than
primary dentin
There is usually a bend in the
tubules where primary and
secondary dentin interface
43
44. Dr. Nithin Mathew - Dentin
SECONDARY DENTIN
Since it is formed after
eruption, the odontoblasts
slightly change direction which
contributes to bending of
dentinal tubules
There is usually a bend in the
tubules where primary and
secondary dentin interface
44
46. Dr. Nithin Mathew - Dentin
TERTIARY DENTIN
By pathologic process or operative procedures,
the odontoblastic processes are
exposed or cut, the odontoblasts
die or survive, depending on the
extend of injury
If they survive, dentin that is
produced are called reactionary or regenerated
dentin
Killed odontoblasts are replaced by the migration
of undifferentiated cells arising in the deeper
layers of the pulp to the dentin interface
46
47. Dr. Nithin Mathew - Dentin
This newly differentiated odontoblasts then begin
deposition of reparative dentin to seal off the zone of
injury as a healing process initiated by the pulp,
Resulting in resolution of the inflammatory process
and removal of dead cells
This type dentin produced by a new generation of
odontoblast-like cells in response to appropriate
stimulus after the death of original odontoblasts is
called Reparative dentin
This reparative dentin has fewer and more twisted
tubules than normal dentin 47
48. Dr. Nithin Mathew - Dentin
Histological difference between reactionary and
reparative dentin is that reactionary dentin is
deficient in acid proteins so it doesn’t stain.
Reactionary dentin appears as either osteodentin
type or orthodentin type
Reparative dentin has structure-less mineralisation
as in bone.
48
50. Dr. Nithin Mathew - Dentin
MANTLE DENTIN
First layer of primary dentin to be deposited
Oldest dentin and produced adjacent to the enamel
in the crown
Can be recognized by he characteristic thick, fan
shaped collagen fibres deposited immediately
subjacent to the basal lamina in histologic sections
Fibres run roughly perpendicular to the DEJ
150µm thick
Slightly less mineralised than underlying dentin
50
51. Dr. Nithin Mathew - Dentin
When viewed under polarised light, the mantle
dentin (RED Band) can be differentiated from the
Circumpulpal dentin (Purple with black dentinal
tubules)
This is due to difference in collagen fibres in
mantle dentin
51
52. Dr. Nithin Mathew - Dentin
CIRCUMPULPAL DENTIN
Formed after the layer of mantle dentin has been
deposited
Constitutes major part of primary and secondary
dentin
Hydroxy appatite crystals are deposited on the
surface and within the fibrils and continue to grow
as mineralization proceeds, resulting in an
increased mineral content of dentin
Circumpulpal dentin is mineralised through
calcospherites in the mineralisation front between
predentin and mineralizing dentin
52
53. Dr. Nithin Mathew - Dentin
As the calcospherites enlarge, they fuse with the
adjacent calcospherites until the dentin matirx is
completely mineralised
53
54. Dr. Nithin Mathew - Dentin
INCREMENTAL LINES
The incremental lines of
Von Ebner or imbrications
lines appear as fine lines or
striations in dentin
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 54
55. Dr. Nithin Mathew - Dentin
The course of the lines indicates the growth
pattern of the dentin
Some of these incremental lines
are accentuated because of
disturbances in the matrix and
remineralization process.
Such lines are known as
Contour lines of Owen
These lines represent hypocalcified
bands
55
56. Dr. Nithin Mathew - Dentin
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
56
60. Dr. Nithin Mathew - Dentin
INTERGLOBULAR DENTIN
Sometimes mineralization of dentin begins in small
globular areas that fail to fuse into a homogenous
mass.
This results in zones of hypomineralisation btwn
the globules. These zones are called interglobular
dentin.
Forms in crowns of teeth in the circumpulpal dentin
just below the mantle dentin
Seen in dental anomlies (hypophosphatasia) 60
61. Dr. Nithin Mathew - Dentin
The dentinal tubules pass uninterruptedly, thus
demonstrating a defect of mineralization and not of
matrix formation
61
62. Dr. Nithin Mathew - Dentin
GRANULAR LAYER
There is a zone adjacent
to the cementum that
appears granular known
as Tome’s granular layer
It slightly increases in amount from the CEJ to
the root apex
Caused by coalescing and looping of the terminal
portions of the dentinal tubules
62
64. Dr. Nithin Mathew - Dentin
PHYSICAL & CHEMICAL PROPERTIES
Physical
Light yellowish in color becomes darker with age
Viscoelastic (86GPa) and subject to slight deformation
unlike enamel (11-20GPa) which is hard and brittle
Harder(68kg/mm2) than bone but considerably softer
than enamel(343kg/mm2)
Lower content of mineral salts in dentin renders it more
radiolucent than enamel
64
65. Dr. Nithin Mathew - Dentin
Provides resiliency to the crown which is necessary
to withstand the forces of mastication
65
66. Dr. Nithin Mathew - Dentin
Chemical
20% organic matter
10% water
70% inorganic material
66
67. Dr. Nithin Mathew - Dentin
Organic substances:
Type I collagenous fibrils
Type V collagenous fibrils (minor)
Non collagenous proteins:
•Dentin phosphoprotien (DPP)
•Dentin matrix protein 1 (DMP1)
•Dentin sialoprotein (DSP)
•Bone sialoprotein (BSP)
•Osteopontin, Osteocalcin
Proteoglycans
Phospholipids
Growth factors:
•Bone morphogenetic proteins (BMP)
•Insulin like growth factors (IGFs)
•Transforming growth factors β (TGF- β)
67
69. Dr. Nithin Mathew - Dentin
Type I collagen is the principal type of collagen
found in dentine
Inorganic crystals are plate shaped and much
smaller than hydroxyl apatite crystals in enamel
Dentin also contains small amounts of phosphates,
carbonates and sulphates.
69
70. Dr. Nithin Mathew - Dentin
INNERVATION OF DENTIN
Nerve fibres were shown to accompany 30-70% of
the odontoblastic process and these are referred
to as intratubular nerves
These nerves and their terminals are found in
close association with the odontoblasts process
within the tubule
70
71. Dr. Nithin Mathew - Dentin
Theories of pain transmission through dentin
3 basic theories of pain conduction through dentin
Direct neural stimulation
Transduction theory
Modulation theory
“Gate” control / Vibration theory
Hydrodynamic theory
71
72. Dr. Nithin Mathew - Dentin
DIRECT NEURAL STIMULATION
According to which nerves in the dentin get
stimulated.
Drawbacks:
The nerves in dentinal tubules are not commonly
seen and even if they are present, they do not extend
beyond the inner dentin
Topical application of local anaesthetic agents do not
abolish sensitivity
Hence this theory is not accepted
72
73. Dr. Nithin Mathew - Dentin
TRANSDUCTION THEORY
According to which the odontoblasts process is the
primary structure excited by the stimulus and that the
impulse is transmitted to the nerve endings in the
inner dentin.
Drawbacks:
Since there are no neurotransmitter vesicles in
the odontoblast process to facilitate the synapse or
synaptic specialization
73
74. Dr. Nithin Mathew - Dentin
MODULATION THEORY
According to which the nerve impulses in the pulp are
modulated through the liberation of polypeptides from
the odontoblasts, when injured.
These substances may selectively alter the
permeability of the odontoblastic cell membrane
through hyperpolarisation, so that pulp neurons are
more prone to discharge upon receipt of subsequent
stimuli
74
75. Dr. Nithin Mathew - Dentin
“GATE” CONTROL / VIBRATION THEORY
This theory states that pain is a function of the
balance between the information travelling into the
spinal chord through large nerve fibre and information
travelling through small nerve fibres.
Large nerve fibres carry Non-nociceptive
information and small nerve fibres carry Nociceptive
information
75
76. Dr. Nithin Mathew - Dentin
According to this theory, A-β fibres which
transmit information from vibration receptors
stimulate inhibitory neurons in the spinal chord,
which inturn act to reduce the amount of pain signal
transmitted from A-δ and C fibres across the midline
of the spinal chord and from there to the brain
76
77. Dr. Nithin Mathew - Dentin
HYDRODYNAMIC THEORY
Most accepted theory
Various stimuli such as heat, cold, airblast
dessication or mechanical or osmotic pressure affect
fluid movement in the dentinal tubules.
This fluid movement either inward or outward,
stimulates the pain mechanism in the tubules by
mechanical disturbance of the nerves closely
associated with the odontoblast and its process
77
78. Dr. Nithin Mathew - Dentin
Thus these endings may act as mechanoreceptos
as they are affected by mechanical displacement
of tubular fluid
78
80. Dr. Nithin Mathew - Dentin
AGE AND FUNCTIONAL CHANGES IN
DENTIN
Vitality of dentin
Odontoblasts and its processes are an integral part of
dentin
And so vitality is understood to be the capacity of the
tissue to react to physiologic and pathologic stimuli,
dentin must be considered a vital tissue
80
81. Dr. Nithin Mathew - Dentin
Dentinogenesis is a process that continues through
out life
Although after the teeth have erupted and have
been functioning for a short time, dentinogenesis
slows and further dentin formation is at a slower
rate. This is secondary dentin
Pathologic changes in dentin such as dental caries,
abrasion, attrition or the cutting of dentin in
operative procedures cause changes in dentin. They
are the dead tracts, sclerosis and the addition of
reparative dentin.
81
82. Dr. Nithin Mathew - Dentin
DEAD TRACTS
The odontoblastic processes
disintegrate and the empty
tubules are filled with air
Appear black in transmitted light and white in
reflected light
Degeneration is often observed in areas of narrow
pulp horns because of crowding of odontoblasts
82
83. Dr. Nithin Mathew - Dentin
These degenerated empty areas demonstrate
decreased sensitivity
Seen to a greater extend in older teeth
Dead tracts are probably the initial step in the
formation of sclerotic dentin
83
84. Dr. Nithin Mathew - Dentin
SCLEROTIC/TRANSPARENT DENTIN
84
Caries, attrition, abrasion, erosion or
cavity preparation causes collagen fibres
and apatite crystals to begin appearing
in the dentinal tubules
This blocking of tubules may be considered as a
defensive reaction of dentin
These apatite crystals are initially only sporadic
in a dentinal tubule but gradually fill it with a
fine meshwork of crystals
85. Dr. Nithin Mathew - Dentin
As this continues, the tubule lumen is obliterated
with mineral which appears very much like the
peritubular dentin
The refractive indices of dentin in such areas
become transparent
Transparent in transmitted and dark in reflected
light
There is decreased permeability of dentin
85
86. Dr. Nithin Mathew - Dentin
DENTINAL FLUID
Free fluid occupies 1% of superficial dentin and 22%
of total volume of deep dentin
Ultrafiltrate of blood from pulp capillaries
Contains plasma proteins
Serve as a sink from which injurious agents can
diffuse into the pulp producing inflammatory
response
Also serve as a vehicle for egress of bacteria from a
necrotic pulp into periradicular tissue. 86
87. Dr. Nithin Mathew - Dentin
CLINICAL CONSIDERATIONS
Restorative procedures
Cavity preparation – minor routine procedure
– Crisis from the perspective of the pulp
Fluid shifts
Simple restorative procedure – profound
effects on the pulp
87
88. Dr. Nithin Mathew - Dentin
Sensitivity of dentin
On root areas exposed due to receded
gums or periodontal disease.
Root of a tooth becomes exposed - it does not
have a layer of enamel but cementum
Overzealous brushing or using a very abrasive
toothpaste can also cause abrasion of the tooth’s
enamel surface and expose dentin.
Very acidic diet –– can cause tooth erosion and
dissolve the tooth surface, exposing the dentin. 88
89. Dr. Nithin Mathew - Dentin
Permeability of dentin
Tubular structure of dentin provides passage of
solutes and solvents across dentin
Lowest at the DEJ and highest at the pulp –
diameter increases with depth
Divided into 2 categories
Transdentinal movement – fluid shifts in
hydrodynamic stimuli
Intradentinal movement – as occurs
infilteration of hydrophilic resins into
demineralised dentin surfaces
89
91. Dr. Nithin Mathew - Dentin
Smear layer & Smear plugs
Smear Layer - term most often used to
describe the grinding debris left on
dentin by cavity preparation
Cutting debris when forced into dentinal tubules,
it forms plugs known as smear plugs
Smear layer : 1-3 µm
Smear plug : 40 µm
Significance - Lowers the permeability of dentin
surface 91
93. Dr. Nithin Mathew - Dentin
Remaining dentin thickness (RDT)
The major factor in odontoblast response and in
dentin formation
Odontoblast injury increases as the cavity RDT
decreases.
Below 0.25 mm the number of odontoblasts
decreases by 23%, and minimal reactionary dentin
repair is observed.
93
94. Dr. Nithin Mathew - Dentin
Affected & Infected dentin
Infected dentin is that part of dentin which is
contaminated and contains the microorganism with
their toxins, and demineraliaed dentin.
Affected dentin is not occupied by microorganism it
just contains the toxins produced by microorganisms
of the infected dentin, and also there is
demineralization.
94
95. Dr. Nithin Mathew - Dentin
The collagen fibres are denatured in Infected
dentin while in Affected dentin, the collagen fibres
demonstrates cross-banding and is physiologically
remineralizable
95
96. Dr. Nithin Mathew - Dentin
CONCLUSION
Developmentally pulpal cells produce dentin,
nerves and blood vessels.
Although dentin and pulp have different
structures, once they are formed, they react to
stimuli as a functional unit.
Exposure of dentin through attrition, caries or
trauma produces profound pulpal reactions that
tend to reduce permeability and stimulate
formation of additional dentin. 96
97. Dr. Nithin Mathew - Dentin
REFERENCES
Orbans oral histology and embryology
Tencates Oral histology
Dental Pulp – Seltzer and Bender
Pathways of the pulp - Cohen
97