Dentin

Dr. Nithin Mathew - Dentin
CONTENTS
 Introduction
 Stages of tooth development
 Structure of dentin
 Dentinal tubules
 Peritubular dentin
 Intertubular dentin
 Predentin
 Primary dentin
 Secondary dentin
 Tertiary dentin
 Interglobular dentin
 Granular layer 2

Incremental lines
Odontoblastic processes
 Properties
Physical
Chemical
 Innevervation of dentin
 Theories of pain transmission
Direct neural stimulation theory
Transduction theory
Hydrodynamic theory 3

 Age & functional changes
Vitality of dentin
Dead tracts
Sclerotic dentin/ transparent dentin
 Clinical considerations
 Conclusion
 References
4

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

 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

 But the odontoblasts cell bodies remain external to
dentin, but their processes exist within tubules in
dentin.
7

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

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

 The dental lamina has the full potential to induce
tooth formation by dictating the fate of the
underlying ectomesenchyme.
10

11
a : Nasal Septum
b : Tongue
c : Palatal Processes
d : Dental lamina

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
A : Ectodermal outgrowth
B : Dental Mesenchyme
C : Tongue
D : Oral Cavity Space
E : Oral Ecotoderm

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

 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
a : Outer Dental Epithelium
b : Inner Dental Epithelium
c : Stellate Reticulum
d : Dental Papilla
e : Dental lamina

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

 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

 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

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

 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
a : Nerve Bundle
b : Alveolar Bone
c : Vasculature
d : Oral Ectoderm
e : Tongue

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

 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

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

 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

 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

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

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

 Well mineralised
 Provide tensile strength to dentin
33

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

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

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

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

 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

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

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

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

 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

 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

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

 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

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

 As the calcospherites enlarge, they fuse with the
adjacent calcospherites until the dentin matirx is
completely mineralised
53

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

 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

 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

57
Incremental lines of Von Ebner

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

 The dentinal tubules pass uninterruptedly, thus
demonstrating a defect of mineralization and not of
matrix formation
61

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

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

 Provides resiliency to the crown which is necessary
to withstand the forces of mastication
65

Chemical
 20% organic matter
 10% water
 70% inorganic material
66

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

 Inorganic substances:
•Calcium hydroxy appatite crystals
68

 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

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

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

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

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

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

“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

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

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

 Thus these endings may act as mechanoreceptos
as they are affected by mechanical displacement
of tubular fluid
78

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

 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

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

 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

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

 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

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

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

 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

 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

 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

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

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

The collagen fibres are denatured in Infected
dentin while in Affected dentin, the collagen fibres
demonstrates cross-banding and is physiologically
remineralizable
95

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

REFERENCES
 Orbans oral histology and embryology
 Tencates Oral histology
 Dental Pulp – Seltzer and Bender
 Pathways of the pulp - Cohen
97

Dentin

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