Dentinal tubules and its content final/cosmetic dentistry courses

Dentinal tubules and
its content
INDIAN DENTAL ACADEMY
Leader in continuing Dental Education
www.indiandentalacademy.com

 Tencate’s oral histology and embryology-7th edition
 Tencate’s oral histology and embryology-8th edition
 Oral histology-Berkovitz,3rd edition
 Oral histology-Berkovitz,4th edition
 Orban’s oral histology,13th edition
References

LEARNING OBJECTIVES
O At the end of the seminar the learner should be
able to describe
O Dentin and its composition
O What are dentinal tubules
O Contents of the dentinal tubules
O Theories of pain transmission
O Primary, secondary and tertiary dentin
O Age and functional changes

O The dentin forms bulk of the tooth tissues and occupies both the
crown and the root.
O It is surrounded by enamel in the crown
and cementum in the root.

O The organic substance consists mainly of type I collagen fibres
embedded in the ground substance of mucopolysaccharides.
O The inorganic component consists of plate shaped
hydroxyapetite crystals.

O Dentin is permeated by tubules, the dentinal tubules
that run from the pulpal surface to the enamel-
dentine and cementum-dentine junctions.
O The dentine tubules follow a curved,
sigmoid course-the primary curvatures.

O Starting at right angles from the pulpal surface
the first convexity of this doubly curved
course is directed toward the apex of the tooth.
O These tubules end perpendicular to the dej and
dcj.
O Branches of the dentinal tubules near the
terminals are referred to as terminal branches.

O Near the root tip and along the incisal edges
and cusps the tubules are almost straight.
O Over their entire length the tubules exhibit
minute relatively regular secondary curvatures
that are sinusoidal in shape.

O The tubules are longer than the dentin, and are
thick because they curve through dentin.
O The ratio between the outer and inner surfaces
of the dentin is about 5:1.

O Accordingly, the tubules are farther apart in
the peripheral layers and are more closely
packed near the pulp .
O In addition, they are larger in diameter(3 to
4um) near the pulp cavity and smaller (1um) at
their outer ends.

O The ratio between the numbers of tubules per unit
area on the pulpal and outer surfaces of the dentin
is about 4:1.
O Near the pulpal surface of the dentin the number
per square mm varies between 50,000 and 90,000.
O There are more tubules per unit area in the crown
than in the root.

O The dentinal tubules have lateral branches
throughout dentin, which are termed canaliculi or
microtubules.
O These canaliculi are 1um or less in diameter and
originate more or less at right angles to the main
tubule every 1 to 2um along its length.
O Some of them enter adjacent or distant tubules
while others end in the intertubular dentin.

O Peritubular dentin
O The dentin that immediately surrounds the
dentinal tubules.
O This dentin forms the wall of the tubules .
O It is more highly mineralised than the dentin
present between the tubules-intertubular dentin.

O Peritubular dentin differs from the intertubular
dentin by its matrix composition.
O The crystal arrangement appears to be similar.
O It is twice as thick in outer dentin(0.75um)
than in inner dentin(0.4um)

O Types of Dentin
O Primary Dentin: dentin formed prior to root formation or
completion.
O Two Types:
O Mantle Dentin (M) is the area of initial dentin matrix
formation and is the first formed dentin.
O Some Investigators disagree on the location of mantle dentin
and believe it is only located in the crown of the tooth.

O TenCate and Gartner located it in both the
crown just below the DEJ and the root of the
tooth.
O Mantle Dentin is ~20 micrometers thick and
slightly less mineralized than circumpulpal dentin.
O The fibers are perpendicular to the DEJ in the
crown.

O Made principally of Large coarse bundles of
type I collagen.
O However the first sign of dentin formation
contains vonKorff’s fibers, which are large-
diameter Type I collagen fibrils.

O Circumpulpal dentin forms the remaining and the bulk
of primary dentin.
O The collagen fibers are much narrower (~0.05mmthick)
than mantle dentin..
O It is more mineralized than mantle dentin.
O It has more compactly arranged collagen fibers than
mantle dentin.

O Secondary Dentin: dentin produced after root
formation or completion. (NOT due to trauma)
O Secondary Dentin is a narrow band of dentin
around the pulp chamber .
O It is formed subsequent to root completion.
O It is not formed as a response to trauma.

O It is formed at a slower rate than primary dentin.
O It contains fewer tubules than primary dentin.
O It is formed in an unequal fashion and more
secondary dentin produced on the roof and floor of
the pulp than on the walls.

Composition of dentinal tubules
1.Odontoblast process
2.Nerve fibres
3.Unmineralised collagen fibrils

O The odontoblast process are the cytoplamic
extensions of the odontoblasts.
O The odontoblast cells reside in the peripheral pulp at the pulp-
predentin border and their process extend into the dentinal
tubules.
O The processes are largest in diameter near the pulp(3 to 4um)and
taper to approximately 1um further into the dentin.

O The odontoblast cell bodies are approx 7um in dia
and 40um in length.
O The junctions between odontoblasts may be of
gap junctions,tight junctions and desmosomal
junctions.
O The life span of the odontoblasts is equal to the
age of the tooth as once differentiated cannot
undergo further division.

O The odontoblastic processes narrow to about half the
size of the cell as they enter the tubules.
O Evidence shown by transmission electron microscopy
revealed that dentinal tubules 200 to 300um from the
pulp contain processes.
O Scanning electron microscopy, have shown what
appears to be processes at the dentinoenamel junctions.

O Cryofactured human teeth revealed the odontoblast
process to extend to the dej.
O The organic lining membrane of the tubule-lamina
limitans, not the odontoblastic process.
O Investigations using immunoflourescent techniques
revealed tubulin throughout the thickness of dentin.

O It is appropriate to consider that some odontoblast
processes traverse the thickness of dentin.
O In other areas a shortened process may be
characteristic in tubules that are narrow or obliterated
by mineral deposit.
O In the other areas a shortened process may be
chatacteristic in tubules that are narrow or obliterated
by mineral deposit.

O The odontoblast process is composed of microtubules
of 20um in dia and small filaments 5 to 7.5um in dia.
O The microtubules and intermediate filaments run
longitudinally throughout the tubules.
O Occasionally mitochondria, dense bodies resembling
lysosomes, microvesicles and coated vesicles that may
open to the extracellular space are also seen.

O The odontoblast processes divide near the dej and
may indeed extend into the enamel as enamel
spindles.
O Periodically along the course of the processes
side branches appear that extend laterally into the
adjacent tubules.

O Intratubular nerves
O Nerve fibres accompany 30 to 70% of the odontoblastic process.
O These referred to as intratubular nerves.
O Dentinal tubules contain numerous nerve
endings in the predentin and inner dentin.

O Most of these small vesiculated endings are located
in the tubules in the coronal zone, specially in the
pulp horns.
O There may be single terminals or several dilated
and constricted portions.
O In either case, the nerve endings are packed with
small vesicles, either electron dense or lucent,
depends on whether there has been discharge of
their neurotransmitter substance.

O They interdigitate with the odontoblast process,
indicating and intimate relationship to this cell.
O Synapse like relation between the process and
nerve fibres were demonstrated.
O Most of these are terminal processes of the
myelinated nerve fibres of the dental pulp.

O Theories of pain transmission through dentin
O 1.Direct neural stimulation
O 2.Fluid or Hydrodynamic theory
O 3.Transduction theory

O Direct neural stimulation, by which the nerves in the
dentin get stimulated.
O The nerves in the dentinal tubules are not commonly
seen and even if they are present, they do not extend
beyond the inner dentin.
O Topical application of local anesthetics do not
abolish sensitivity. Hence this theory is not accepted.

O Fluid or hydrodynamic theory
O Various stimuli such as heat, cold, air blast desiccation,
or mechanical or osmotic pressure affect fluid
movement in the dentinal tubules.
O 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.

O These endings may act as mechanoreceptors as
they are affected by mechanical displacement
of the tubular fluid.

O Transduction theory
O This theory presumes that the odontoblast process
is the primary structure excited by the stimulus and
that the impulse is transmitted to the nerve endings
in the inner dentin.
O This is not a popular theory since there is no
neurotransmitter vesicles in the odontoblast process
to facilitate the synapse or synaptic specialization.

Age and functional changes
1. Physiologic regular secondary dentin
2 Pathologic irregular secondary (tertiary) dentin
3. Transparent (sclerotic) dentin

Physiologic regular secondary
dentin
• This is the type of dentin formed under
Physiologic conditions after complete root
formation.
• It is deposited continuously as long as the
pulp is vital.
• It is formed at a lower rate and is separated
by a darkly stained line from primary dentin

• It has less number of tubules.
• It occurs in the entire pulpal surface.
• Higher deposition at the roof and floor of
the pulp chamber.

Physiologic regular secondary
dentin
• The size of the pulp cavity decreases and obliteration of
the pulp horns.
• The course of the dentin canals is more irregular.

Pathologic irregular secondary
dentin
• It is also known as tertiary or reparative
dentin
• This type of dentin is formed as a protection for
the pulp against severe stimulus (pathological
conditions or irritations), such as
• Attrition
• Caries
• Preparations
• It is formed at a localized area (e.g. pulp horn)
• Some UMC in the subodontoblastic layer
differentiate to new odontoblast to form dentin.

• The number of the tubules is reduced.
• Tertiary dentin has frequently twisted tubules.
• Reparative dentin is separated
from other types by a darkly
stained line.

O Dead Tracts (empty dentinal tubules that lead
directly to pulp)
O If the carious demineralization of enamel
reaches dentin, the carious lesion allows
bacteria to enter the dentinal tubules.
O Odontoblasts can then be either damaged or
killed, as well as their processes.

O If killed, then there will be areas of dentin with
no odontoblasts.

Sclerotic Dentin
O Sclerosis of dentin is the naturally occurring deposition
of minerals within tubules that results in the occlusion of
the dentinal tubules and a thicker layer of peritubular
dentin.
O It is highly mineralized.
O Deposited inside the periphery of the tubules.
O The tubules become smaller in diameter and less
permeable and so transmit stimuli to a lesser degree.www.indiandentalacademy.com

O Markings on Dentinal Tubules
O Length of the Dentin tubule
O i. Has striations called Daily Imbrication
Lines of Von Ebner
O In between the lines is the amount of dentin
that you make in 1 day (4-8μm)

O ii. Wide arcs of rings in dentin are called Contour
Lines of Owen
O a. Result from metabolic disturbances during
development.
O b. Indicative of health of person during dentin
formation.
O Hypocalcified dentin.

O Permeability of dentin
O Dentin tubules becomes occluded by growth of
peritubular dentin or by reprecipitation of minerals
from demineralised areas of dental caries.
O Exposed dentinal surface becomes hypermineralised.
O Dentin permeability depends upon the patency of
dentinal tubules.

O Tubular occlusion, smear layer formation, lack
of tubular communication between primary
and irregular secondary dentin will result in
reduced permeability.
O Reduction in dentin permeability would lessen
the sensitivity of dentin.

O Dentin permeability increases rapidly as the pulp
chamber is approached because the number and
diameter of the tubules are more per unit area
towards pulp than towards periphery.
O The outward flow of dentinal fluid and the
odontoblasts act as barriers for entry of bacteria or
their toxins.

O Thank you

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