Dentine lecture

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.

Formation of dentin begins when
the tooth germ reach the bell stage.
The dental papilla is the formative
organ of dentin, formed of
ectomesenchymal spindle shaped cells
in loose intercellular substance,
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 organizing effect
(induction) that coming from the
inner dental epithelium.
Dentinogenesis

A good blood supply and alkaline
phosphatase E are required thus, the
dental papilla is the formative organ of
dentin and eventually 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.

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

1. Odontoblast differentiation:
Under the inductive
effect of the inner
dental epithelium,
the peripheral
ectomesenchymal
cells of the dental
papilla differentiate
into odontoblast.

1. Odontoblast differentiation:
Before differentiation, the
inner dental epithelium is
separated from the dental
papilla by a thin basement
membrane. The peripheral
cells of the papilla are spindle
and separated by great amount
of ground substance. As
induction occur, they come into
contact with the basement
membrane. They assume a
short columnar shape and
aligned in a single raw along
the basement membrane.

2. Formative stage:
L/M: it is large, plump cell with an
open faced nucleus situated basally
and a basophilic cytoplasm.
E/M: the apical basophilic cytoplasm
contains the organelles required for
the synthesis of dentin matrix
(pronounced Golgi complex-
prominent rough endoplasmic
reticulum- increased mitochondria)
The secretory odontoblasts form
extensive junction complexes and gap
junction to form distinct row of
odontoblasts, the cell also exhibit
alkaline phosphatase activity which is
necessary for Ca++
transport into the
cell.

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.

These fibers consist of collagen type III. They
originate deep among the odontoblasts, extend
toward the inner dental epithelium, and fan out
in the structurless ground substance
immediately below the epithelium.

2. Formative stage (Odontoblastic process formation):
As the odontoblasts continue to increase in size, they also produce
smaller collagen type I fibrils that orient themselves parallel to the
future dentino-enamel junction. As the first layer of dentin is
deposited, the odontoblastic layer retract from the basement
membrane. The cells when they move into pulpal direction, they
leave behind a single process which become enclosed in a tube
formed of dentin called dentinal tubule. With the successive
deposition of dentin both the process and the tubule grow in length.

3. Quiescent 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.

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.

1. Formation of predentin (dentin1. Formation of predentin (dentin
matrix formation):matrix formation):
The first indication of
predentin formation is the
development of bundles of
fibrils among the fully
differentiated odontoblast.
These bundles were known as
Von Kroff’s fibers, that form
the major component of the
first formed thickness of
dentin and are attached to the
basement membrane of the
inner dental epithelium.

These fibers ( Korff’s fibers) ,These fibers ( Korff’s fibers) ,
were thought to be secreted bywere thought to be secreted by
the subodontoblastic cells of thethe subodontoblastic cells of the
dental papilla. They have andental papilla. They have an
argyrophilic reaction ( stain blackargyrophilic reaction ( stain black
with silver). Under E/M, it waswith silver). Under E/M, it was
found that this black stain is offound that this black stain is of
the ground substances among thethe ground substances among the
cells and not due to the thickcells and not due to the thick
collagen fibers. So, the formationcollagen fibers. So, the formation
and secretion of these fibers isand secretion of these fibers is
proved to be from odontobastsproved to be from odontobasts
and not from other cells.and not from other cells.

After odontoblasts differentiated, the collagen formation
begins in ribosomes sites of RER as procollagen, then pass
to Golgi complex where they are glycosylated to be
transferred as secretory vesicles towards the secretory
poles of the cells.
Once the secretory vesicles secreted outside the cell, the
procollagen molecules aggregated as large fibers of type I
collagen fibers in ground substance which is the product of
odontoblasts incorporated with some of pre-existing
substance of the cell free zone to form Mantle dentin.
The large collagen fibrils are 0.1-0.2 µm in diameter; these
fibrils are aligned at right angles to the basement
membrane, while in the mantle dentin of the root, they are
parallel to it.

The first formed thickness of
dentin is the mantel dentin. As
dentin is further deposited, the
first formed fibers fade
gradually and smaller fibrils
constitute a network in the
dentin subsequent to the
mantle dentin, i.e.
circumpulpal dentin.
Odontoblasts function in the
formation of both the collagen
fibers and the acid
mucopolysaccharides of the
dentine matrix

•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.

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.

2. Maturation (mineralization) of predenitn:2. Maturation (mineralization) of predenitn:
It occurs at a rate that parallel to matrix
formation, and both formation and
maturation of predentin begin at the tip of
the crown and proceeding in a rhythmic
pattern to be gradually completed
cervically. It does not occur until a fairly
wide band of matrix is formed. Thus until
the matrix is completed , the width of
predentin remain constant (10-20 um).
After the odontoblasts form a wide band of
predentin, they bud off matrix vesicles
which are small vesicle exit from their
plasma membrane into the extra cellular
organic matrix.
These vesicles are rich in calcium and
phosphate ions and contains alkaline
phosphatase enzyme, their function is to
provide a special micro-environment to
form the first hydroxyapatite crystals.

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.

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.

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

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.

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

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.

• Colour
• Hardness
• Brittleness
• Permeability
• Thickness
• Radiograph

Thickness : 3-Thickness : 3-
10mm or even10mm or even
moremore
Radiograph: moreRadiograph: more
radiolucent thanradiolucent than
enamel, moreenamel, more
radiopaque thanradiopaque than
cementum andcementum and
bone due to lowerbone due to lower
mineral contentmineral content

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

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

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.

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.

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.

Histological Structure
Adjacent to the pulpal end of dentin, the odontoblasts are arranged
in a well defined layer, sending their odontoblastic processes
through dentin. Each odontoblast sends one odontoblastic process
that passes in one dentinal tubule where it traverse the dentin
thickness. Adjacent to outer dentin surface, the odontoblastic
processes end by formation of several branches
I. Odontoblast

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

II. Dentinal Tubules with secondary branches

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.

4. The number of
tubules is greater in the
crown than in root/unit
area.
5. The tubules have
lateral branches through
their course known
canaliculi, in which the
lateral branches of
odontoblastic processes
traverse.

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

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

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.

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

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.

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.

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

IV. Peritubular dentin

V. Intertubular dentin

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.

A. Incremental lines of Von Ebner:

B. Contour lines of Owen:

C. Neonatal line:

II. Interglobular dentin:

What about dentinalWhat about dentinal
tubules through thesetubules through these
areasareas??

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.

Theories of granular layer of
Tomes occurrence:
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

Age changes (Repair & Defence Mechanisms)
I. Physiologic secondry dentin:

Repair & Defence Mechanisms
I. Physiologic secondry dentin:

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

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.

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.

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.

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.

IV. Sclerotic dentin ( transparent dentin ):
Sclerotic dentin can be seen in:
1. Eldery tooth root.
2. Around dentinal part of type B & C enamel lamellae.
3. Under slowly progressive caries.
And is characterized by:
1. Harder and denser than normal dentin.
2. Appears light in transmitted light, and dark in reflected
light.

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

Dentine sensitivity
This theory denotes that
dentin is innervated,
however, the nerve fibers of
dentin are proved to be only
limited to the predentin and
in very thin layer of dentin
lying beside the pulp tissue.
as a matter of fact, the
nerve fibers are not
demonstrated beyond these
regions or at the
dentinoenamel area.
I. The direct neural stimulation:

Dentine sensitivity
The nerve fibers arise from the
plexus of Raschkow, enter the
predentin, and return to region
the plexus again.

Dentine sensitivity
The controversy:
1. sensitivity of dentin is more at the dentinoenamel junction,
while the nerve endings didn’t reach that area.
2. The plexus of Raschkow and the intratubular nerves don’t
establish themselves until after eruption by time although the
newly erupted teeth are sensitive
3. The application of local anesthetics to exposed dentin doesn’t
eliminate dentin sensitivity.

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

Dentine sensitivity
The controversy:
1. The demonstration of a synaptic relationship between the
odontoblast and pulpal nerves has not found.
2. The membrane potential of odontoblast measured in vitro is too
low to permit transduction.
3. The application of local anesthetics to exposed dentin doesn’t
eliminate dentin sensitivity.
2. Transduction theory

Dentine sensitivity
This theory proposed to explain dentin sensitivity
involves movement of fluid through the dentinal
tubules. This hydrodynamic theory, which fits
much of the experimental and morphologic data,
proposes that fluid movement through the tubule
distorts the local pulpal environment and is sensed
by the free nerve endings in the plexus of
Raschkow. Thus
2. Hydrodynamic theory:

Dentine sensitivity
The agreements:
1. When dentin is first exposed, small blebs of fluid can be seen on
the cavity floor. When the cavity is dried with air or cotton wool,
a greater loss of fluid is induced, leading to more movement and
more pain.
2. The increased sensitivity at the dentinoenamel junction is
explained by the profuse branching of the tubules in this region.
3. The hydrodynamic theory also explain why local anesthetics,
applied to exposed dentin, fail to block sensitivity and why pain is
produced by thermal change, mechanical proping, hypertonic
solutions, and dehydration.
2. Hydrodynamic theory

Clinical considerations
1. Metallic restorations are excellent
thermal conductors. Therefore it is
appreciate to replace a cement base under
these restorations to protect the pulp by
minimizing pain conduction.
2. Because of the permeability of dentin, in
cavity preparation, sealing of dentinal
tubule is a requisite of effective restorative
dentistry.

Dentine lecture

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