Dentin is the hard connective tissue that forms the bulk of the tooth. It consists of tubules throughout its thickness and determines the shape of the tooth crown. Dentin is formed by odontoblasts that differentiate from dental papilla cells and produce an organic matrix that becomes mineralized. There are three types of dentin - primary, secondary, and tertiary. Primary dentin forms most of the tooth, secondary dentin is deposited after root formation, and tertiary dentin is reparative dentin deposited in response to stimuli. Dentin has a tubular structure and contains both collagen and hydroxyapatite crystals.

1. DENTIN
Complex, intricate, elusive yet fascinating, alluring, amazing. I m not
describing girls but that tissue that makes up the bulk of our tooth structure –
DENTIN.
1) Introduction
2) Development
- Dentinogenesis
- Mineralization.
3) Physical and Chemical properties.
4) Structure of dentin.
5) Types of dentin.
- Primary
- Secondary
- Tertiary
- Pre-dentin.
6) Histology of Dentin.
- Dentinal tubules.
- Intratubular/ peritubular dentin.
- Intertubular dentin.
- Interglobular dentin.
- Incremental lines.
- Granular layer of Tomes.
- Odontoblast process.
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2. 7) Innervation of Dentin
- Intratubular nerves.
- Theories of pain transmission.
8) Age and functional changes.
- Vitality of dentin.
- Dead tracts.
- Sclerotic dentin.
9) Junction of dentin.
10)Clinical considerations:
11)Dentinal anomalies (Developmental)
- Dentin dysplasia.
- Dentinogenesis imperfecta.
- Regional odontodysplasia.
12)Conclusion
13)Bibliography.
INTRODUCTION
It is said that in order to recognize and understand the abnormal, it is
necessary to have an understanding of the normal. So, let us delve into the
myriad features of this second most hardest tissue of the human body and the
armour of the dental pulp – dentin – a tissue that is vital and vibrant since it
contains living protoplasm.
Going back in time, Anthony von Leuwenholk in 1675, explained the
tubular structures of dentin Von Purkinje and Retzins explained about dentinal
2

3. tubules. John Hunter specified it as a hard tissue and Curier gave the name
“Ivory” to dentin. Von Ebner showed presence of collagen fibres in the
intertubular dentin.
DENTINOGENESIS: Starting at the beginning, dentinogenesis or the
process of formation of dentin is a marvel in itself. Since dentin form slightly
before enamel, being the first calcified tissue to be deposited during tooth
embryogenesis, it determines the shape of the crown including the cusps, ridges
and size of roots.
Dentin is the hard connective tissue that forms the bulk the tooth and is
located in both the crown and root of the tooth.
 It consists of tubules throughout its thickness.
 Since it forms slightly before enamel, it determines the shape of the
crown, including the cusps and the ridges.
 Physically and chemically the dentin closely resembles bone.
[The main difference is that some of the osteoblasts that form bone
become enclosed within its matrix substance as osteocytes, whereas the dentin
contains only the processes of the cells that form it].
 Dentin is considered as a living tissue because it contains within its
tubules the processes of the specialized cells, the odontoblasts – the cells
that produce dentin.
3

4. Dentinogenesis:
Dentin is formed by cells the odontoblasts that differentiate from the
ectomesenchymal cells of the dental papilla. The odontoblasts produce an
organic matrix that becomes mineralized to form dentin. Thus the dental papilla
is the formative organ of dentin. Dentinogenesis is a subset of odontogenesis
and starts at the advanced bell stage or the histodifferentiation stage exerting a
reciprocal inductive effect on enamel formation.
Matrix formation involves:
1) Fibrillogenesis; 2) maturation; 3) calcification.
Dentinogenesis begins at the cusp tips with collagen production. As the
odontoblasts differentiate they change from an ovoid to a columnar shape and
nuclei become basally oriented. One or several processes arise from the apical
end of the cell in contact with the basal lamina. The length then increases to
approx. 40µ with width remaining constant. Proline appears in the RER (rough
surface endoplasmic reticulum) and Golgi apparatus. As the cell recedes it
leaves behind a single extension and the several initial processes join into one,
which become enclosed in a tubule. As matrix formation continues, the
odontoblast process lengthens as does the dentinal tubule. Initial increments are
4µ/day. After eruption slows to 1µ/day. After root development may decrease
further although reparative dentin may form at 4µ/day.
As each increment of predentin is formed, it remain a day before it is calcified.
4

5. An interesting phenomenon and mystery are the von Korff’s fibres. They have
been described as the initial dentin deposition along the cusp tips and because
of the arzyrophilic resorption (stain black with silver). It was long believed that
bundles of collagen formed among odontoblasts. Recently it was revealed that
it was ground substance among cells that stained. Consequently, all predentin is
formed is the apical end of the cell and forming tubule wall. A finding constant
with collagen synthesis in connective tissue and bone. The odontoblasts secrete
both collagen and the intercollagen substance proteoglycans. Thus it is
equivocal whether cell dentin collagen is derived from odontoblast activity. So,
the term von Korff fibre connotes fibres were the only source of mentle dentin
collagen and are densly incorrect.
A special look here is made at the odontoblast life cycle having 4 periods:
1. Prepolarizing stage – wherein the ER is most abundant and cells are
pleomorph.
2. Polarizing stage – Cell alignment characterize this stage.
3. Secretory stage – where fully differentiation of odontoblasts occurs into
cytoplasmic zones. Golgi bodies – RER dominate prosecretory granula
become secretory granules.
4. Resting stage – occurs after deposition and calcification seen by
shortens of odontoblasts, reduction of organelles etc. These structural
5

6. and morphologic changes are retained until functional demands are
imposed for matrix synthesis of secondary dentin.
Mineralization:
Basically, it occurs by globular (or calcospheric) calcification. Earliest crystal
deposition is in the form of very fine plates of hydroapatite on the surfaces of
the collagen fibrils and in the ground substance. Subsequently, crystals are laid
donw within the fibrils themselves. The crystals associated with the collagen
fibrils are arranged in an orderly fashion with their long axes paralleling the
fibril axes and in rows conforming to the 64nm(640A) striation pattern. Within
the globular islands of mineralization crystal deposition appears to take place
radially from common centers in a so-called spherulite form.
The peritubular region becomes highly mineralized at a very early stage. The
ultimate crystal size remains very small about 3nm (30A) in thickness and
100nm (1000A) in length. The apatite crystals of dentin resemble bone and
cementum and are 300 times smaller than enamel crystals.
PHYSICAL PROPERTIES OF DENTIN
1. Dentin is yellowish in colour (In the teeth of young individuals the
dentin is usually light-yellowish in colour, becoming darker with age)
because light can readily pass through thin, highly mineralized enamel
and be reflected by the underlying dentin, the crown of a tooth has a
yellowish appearance.
6

7.  Thicker / hypomineralized enamel does not permit light to pass
through as readily and in such teeth the crown appears whiter.
2. Dentin is elastic and subject to slight deformation.
 This provides flexibility to prevent # of the overlying brittle enamel.
3. Dentin is somewhat harder than bone, but considerably softer than
enamel (because of inorganic content).
4. The dentin, in radiographs appears more radiolucent (darker) than
enamel and more radiopaque (lighter) than pulp (because of the lower
content of mineral salts).
CHEMICAL COMPOSITION OF DENTIN
Dentin consists of 35% organic matter and water 65% inorganic
material.
Organic Matrix: Consists mainly of collagenous (Type I) fibrils and a ground
substance of mucopolysaccharides (proteoglycans and glycos aminoglycans).
Inorganic Component: Consists mainly of hydroxyapatite crystals (i.e.
calcium phosphte  the final form of this mineral salt is crystalline
hydroxyapatite).
 The hydroxyapatite crystals found in dentin are small, slender and
needle – like, unlike those found in enamel.
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8.  Dentin also contains small amounts of phosphates carbonates and
sulfates.
Types of Dentin
In human teeth, 3 types of dentin can be recognized.
a. Primary Dentin forms most of the tooth and outlines the pulp
chamber of the fully formed tooth.
 The outer layer of the primary dentin is called as the
Mantle dentin. It is located immediately subjacent to the enamel
or cementum  It differs for the rest of the primary dentin.
Width of mantle dentin is 80-100 µm.
 This layer is the 1st
layer formed by newly
differentiated odontoblasts.
 It has an organic matrix consisting of ground
substance and loosely packed thick, fan shaped collagen fibres.
Spaces between fibres are occupied by smaller collagen fibrils
lying more or less parallel to the DEJ or DCJ.
 The matrix is slightly less mineralized than the rest
of the primary dentin.
Circumpulpal Dentin: Forms the remaining primary dentin or bulk of the
tooth.
8

9.  It is formed after the layer of mantle dentin is deposited.
 It represents all of the dentin formed prior to root completion.
 The collagen fibrils in circumpulpal dentin are much smaller in diameter
and are more closely packed together and form an inter-woven network.
They are oriented at right angles to the long axis of the tubules.
 The circumpulpal dentin may contain slightly more mineral than mantle
dentin.
b. Secondary Dentin :
 Secondary dentin is a narrow band of dentin bordering the
pulp and is formed after root formation has been completed.
 It was once thought that 2o
dentin was formed only in
response to functional stimuli, but it has been shown that it is formed
in unerrupted teeth as well.
 Thus 2o
dentin represents the continuing, but much slowed
deposition of dentin by the odontoblasts after root formation has
been completed.
2o
dentin has an incremental pattern and a tubular structure.
 It contains fewer tubules than primary dentin.
9

10.  2o
dentin although deposited around the periphery of the pulp space is
not deposited evenly, especially in the molar teeth.
 There is a greater deposition 2o
dentin on the roof and the floor of the
pulp chamber. This leads to an asymmetrical reduction in the size and
shape of the pulp chamber and the pulp horns.
 Clinically this process is referred to as pulp recession, can be readily
detected in radiographs and are important in determining the form of
cavity preparation in certain dental restorative procedures.
For e.g.: Preparation of tooth for a full crown restoration in young
patients presents a substantial risk of involving one of the pulp horns and of
mechanically exposing the dental pulp.
 In older patients, the pulp horn has receded, presenting less danger.
 There is also evidence that 2o
dentin sclerosis more readily than
primary dentin. This tends to reduce the overall permeability of the
dentin, thereby protecting the pulp.
c. Tertiary Dentin : Is also referred to as reactive / reparative /
irregular 2o
dentin.
The formation of reparative dentin is induced by certain (noxious
stimuli) stimuli such as the following : 1. temperature (extreme heat and
10

11. extreme cold) 2. carious lesions 3. chemical agents (calcium hydroxide and
sodium fluoride) 4. demineralized tooth matrix.
 Unlike primary / 2o
dentin, which is formed along the entire pulp dentin
border, tertiary dentin is produced only by the odontoblasts directly
affected by the stimulus.
The quality and quantity or the degree of tertiary, dentin produced is
related to the intensity and direction of the stimulus.
For example: The stimulus of an active carious lesion cause extensive
destruction of dentin and considerable pulp damage.
In such instances, tertiary dentin is deposited rapidly and displays a
sparse, irregular tubular pattern with frequent cellular inclusions.
Tertiary dentin with such cellular inclusions is sometimes called
“osteodentin”.
On the other hand, if the stimulus is less active, tertiary dentin is
deposited less rapidly, its tubular pattern is more regular and there are fewer, if
any, cellular inclusions.
The main function of the reparative dentin is to protect the pulp from the
inward spread of noxious materials along the dentinal tubules (like bacterial
toxins etc.).
11

12.  This protection is accomplished by the “sealing off” of those involved
dentinal tubules so that their potentially harmful contents do not reach
the dental pulp.
 Because of frequent insults that the teeth are routinely exposed to, the
pulp chambers from aged teeth normally show multiple focii of
osteodentin.
Pre-Dentin
The pre-dentin is located adjacent to the pulp tissue i.e. it lines the
innermost (pulpal) portion of the dentin.
 It is the first formed dentin and is not mineralized.
 It consists of collagen and proteoglycans.
 As the collagen fibres undergo mineralization at the pre-dentin front, the
predentin then becomes dentin and a new layer of pre-dentin forms
circumpulpally.
 Pre dentin is thickest where active dentinogenesis is occurring and its
presence is important in maintaining the integrity of dentin, since its
absence appears to leave the mineralized dentin vulnerable to resorption
by odontoclasts (from the pulp).
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13. HISTOLOGY OF DENTIN
When the dentin is viewed microscopically, several structural features
can identified. These include :
1) Dentinal tubules, 2) intra and intertubular dentin, areas of deficient
calcification called 3) interglobular dentin, 4) increment lines and an area seen
solely in the root portion of the tooth known as the 5) granular layer of tomes
and finally cells of the dentin – odontoblasts.
1. Dentinal Tubules
 The course of the dentinal tubules follows a gentle curve in the crown
and less so in the root, where it resembles on S in shape.
 They start at right angles from the pulpal surface and end angular to the
dentinoenamel and dentinocementum junctions.
 Near the root tip and along the incisal edges and cusps, the tubules are
almost straight.
 Over their entire lengths, the tubules exhibit minute, relatively regular 2o
curvatures.
 The ratio between the outer and inner surfaces of dentin is about 5 : 1
accordingly, the tubules are farther apart in the peripheral layers and are
more closely packed near the pulp.
13

14.  They are larger in diameter near the pulpal cavity (3-4 m) and smaller
at their outer ends (1 m).
 The ratio between the nos of tubules / unit area on the pulpal and outer
surfaces of dentin is about 4:1.
 A few dentinal tubules extend through the dentinoenamel junction into
the enamel for several millimeters. These are termed as enamel spindles.
Dentinal tubules make the dentin permeable, providing a pathway for
the invasion of caries.
Microscopic examination of infected dentin shows that the dental
tubules are packed with micro-organisms well ahead of the decalcified
intertubular dentin.
Drugs and chemicals present in a variety of dental restorative materials
can also diffuse through the dentin and create pulpal injury.
2. Peritubular Dentin / Intratubular Dentin
Around the dentinal tubule is a hypermineralized ring of dentin.
This peritubular dentin is the best calcified of all the mineralized
components of dentin. For this reason, it is clearly demonstrated in cross
sections of ground sections of undecalcified dentin with the light microscopic
(because it is so highly mineralized, it is lost in decalcified sections).
14

15.  This can also be demonstrated by electron microscopy.
 The organic matrix of peritubular dentin is sparse and its collagen
components virtually absent.
 The hydroxyapatite cryptals in the peritubular dentin are extremely
overall and very tightly and closely packed.
(Age change) The formation of intratubular dentin is a slow, continuing
process, which can be accelerated by ext – stimuli;
This process causes a progressive reduction in the size of the tubule
lumen, and on occasion, eventually obliterates the tubule space.
When this occurs in several tubules in the same area, the dentin assumes
a glassy appearance - this dentin is known as Sclerotic dentin – which shall be
dealt with later.
Strictly speaking the term ‘Peritubular dentin’ is incorrect because this
dentin forms within the dentinal tubule (nor around it), narrowing the lumen of
the tubule and is because of more accurately referred to as intratubular dentin.
3. Intertubular Dentin
The main body of the dentin is composed of intertubular dentin. It is
located between the dentinal tubules.
15

16.  Although, it is highly mineralized, this matrix like bone and cementum,
is retained after decalcification, whereas peritubular dentin is not.
 About one half of its volume is organic matrix, specifically collagen
fibres, which are randomly oriented around the dentinal tubules.
 Hydroxyapatite crystals are formed along the fibres with their long axis
oriented parallel to the collagen fibres.
Note : Sheath of Newmann  The Junction of P.T. Dentin and I.T. dentin
reacts differently to stains, acids and alkali treatments. Even in ground section a
distinct difference is noted. Because of these differences, it was once believed
that the intertubular matrices were separated by a kind of membrane called the
“Sheath of Newmann”, Electron microscopic studies however do not confirm
the existence of junctional sheath.
4. Globular Dentin
 Results from accumulation of scattered calcium phosphate
calcospherules. The calcospherules eventually form spheroids or
globules of crystalline hydroxyapatite.
 These calcospherules continue to grow appositionally, resulting in the
formation of the large calcified globules.
16

17. Interglobular Dentin
Interglobular dentin is the term used to describe areas of unmineralized
or hypomineralized dentin that persist within mature dentin.
 The name describes areas where the globular areas of mineralization
(calcospherites) have failed to fuse into a homogenous mass.
 They are especially prevalent in human teeth in which there has been
a deficiency in vit. D or exposure to high levels of fluoride at the
time of dentin formation.
 Interglobular dentin is seen most frequently in the circumpulpal
dentin just below mantle dentin, where the pattern of mineralization
is largely globular.
 Because this irregularity of dentin is a defect of mineralization and
not of matrix formation, the architectural pattern of the tubules
remains unchanged, and they run uninterruptedly through the
interglobular areas.
Incremental Lines
The incremental lines (Von Ebner / Imbrication lines) appear as fine
lines or striations in dentin.
 They run at right angles to the dentinal tubules and correspond to the
incremental lines in enamel or bone.
17

18.  These lines reflect the daily rhythmic, recurrent deposition of dentin
matrix as well as hesitation in the daily formative process.
 The distance between lines varies from 4-8 m in the crown to much
less in the root.
 The daily increment decreases after a tooth reaches functional occlusion.
The course of lines indicates the growth pattern of the dentin.
Contour Lines (Owen): Occasionally some of the incremental lines are
accentuated because of disturbances in the matrix and mineralization process.
 Such lines are readily demonstrated in ground sections and are known as
contour lines and (owen).
Analysis with soft x-ray has shown these lines to represent hypocalcified
bands.
Neonatal Line: In the deciduous teeth and in the 1st
permanent molars, where
dentin is formed partly before and partly after birth, the pre-natal and the post-
natal dentin are separated by an accentuated contour line.
This is termed as the ‘neonatal line’ and is seen in enamel as well as
dentin.
 This line represents the abrupt change in environment and nutrition.
18

19.  The dentin matrix formed prior to birth is usually of better quality than
that formed after birth, and the neonatal line may be a zone of
hypocalcification.
Granular Layer of Tomes
When dentin is viewed under transmitted light in ground sections, a
granular layer of Tomes can be seen just below the surface of the dentin where
the root of the tooth is covered by cementum.
 A progressive increase in the so-called granules occurs from the
cementoenamel junction to the apex of the tooth.
 These granules were once thought to be minute foci of hypocalcified
dentinal matrix (small foci of interglobular dentin).
However, electron microscopic studies have determined that no
collagenous matrix is present in the granules and hence are not small foci of
interglobular dentin.
Most contemporary reports advocate that “Tomes granular layer is a
series of small air spaces probably caused by looping of dentinal tubules in this
region.
Dentino-Enamel Junction
The surface of the dentin at the dentinoenamel junctions is pitted.
19

20.  Into the shallow depressions of the pit rounded projections of the
enamel. This relation assures the firm hold of the enamel cap on the
dentin.
 In sections, the dentinoenamel junction appears not as straight but as a
scalloped line.
 The convexities of the scallops are directed toward the dentin.
The pitted d.E junction is preformed even before the development of
hard tissues and is evident in the arrangement of the ameloblasts and the
basement membrane of the dental papilla.
In microradiographs of ground sections, a hypermineralized zone about
30 m thick can sometimes be demonstrated at the d.E junction. It is most
prominent before mineralization is complete.
INNERVATION AND SENSITIVITY
The question of dentin innervation and dentin sensitivity to a variety of
stimuli has not been resolved in spite of numerous studies.
Many oral histologists are of the opinion that the microspace between
the odontoblast process and the tubule wall is not large enough to
accommodate nerves. Yet electron micrographs have provided substantial
evidence for their presence in the tubule areas, especially close to the pulp.
20

21. Intertubular Nerves: Dentinal tubules contain numerous nerve endings in the
pre-dentin and inner dentin no farther than 100-150 µm for the pulp. Most of
these small vesciculated endings are located in tubules in the coronal zone,
specifically in the pulp horn (because the tubule diameter is the largest here and
the peritubular dentin is very little or almost absent). The nerves and their
terminals are found in close association with the odontoblast process within the
tubule. The nerve endings interdigitate with the odontoblast process, indicating
an intimate relationship to this cell. It is believed that most of these are terminal
process of the myelinated nerve fibres of the dental pulp.
Three theories might explain dentin sensitivity, they are :
1. Direct neural stimulation: (Scott, Stella and Fuentes) Stimuli in some
manner, reach the nerve endings in the dentin and the dentin is
stimulated. There is little scientific support of this theory.
2. Fluid or hydrodynamic theory (Gysi, Braanstorm, Fish) Various stimuli
such as heat, cold, are blast desiccation or mechanical pressure affect
fluid movement in the dentinal tubules.
 The fluid movement either inward / outward, stimulates the pain
mechanism in the tubules by mechanical disturbance of the
nerves closely associated with the odontoblast and its process.
 Thus, these endings may act as mechanoreceptors as they are
affected by mechanical displacement of the tubular fluid.
21

22. 3. Transduction theory: 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.
 This is not a popular theory since there are no
neurotransmitter vesicles in the odontoblast process to
facilitate the synapse.
In summary, no single proposed mechanism fully explains all the facts
related to dentin sensitivity. It may well be that more than one mechanism
operates at any one time.
AGE CHANGES IN DENTIN
Changes in the structural features of dentin occur with age.
These are :
1. Reparative dentin or Tertiary dentin which has been discussed
earlier.
2. Dead tracts.
3. Sclerotic / Transparent dentin.
1. Reparative dentin: If by extensive abrasion, erosion, caries, or operative
procedures, the odontoblast processes are exposed or cut, the
odontoblasts die, or, if they line, deposit reparative dentin.
22

23.  The majority of odontoblasts in this situation degenerate, but a
few may continue to form dentin.
Reparative dentin is characterized as having fewer and more twisted
tubules than dentin.
2. Dead Tracts: Another age related change in dentin structure, which may
be related to pathologic process is the formation of dentin dead tracts.
Here, the odontoblastic cell processes in the involved dentinal tubules
are degenerated, leaving behind empty, air-filled tubules.
The emptied tubules in these areas and the dentin are referred to as
“dead tracts”.
 They are expectedly less sensitive than those in which the processes are
present in the tubules.
 When ground sections are examined with reflected light, the air-filled
tubules are light and unaffected tubules are dark.
 With transmitted light, however, the tubules are dark and the remaining
dentin light.
 Dead tracts generally extend from the dentinoenamel junction to the
corresponding area of the dentin-pulp interface.
In most instances, the dead tracts are sealed at their pulpal aspect by the
forming of reparative dentin.
23

24. Dead tracts are often encountered on the tips and cusps that have been
subjected to abrasive forces sufficient in intensity to cause attrition and they
appear to a greater extent in older teeth.
 Dear tracts are probably the initial step in the formation of sclerotic
dentin.
3. Sclerotic / Transparent Dentin: It is suggested by some researchers that
the drying or dead processes induce, or otherwise enhance
mineralization resulting in the formation of collagen fibres and apatite
crystals within the dentinal tubules.
The calcified tubular space assumes a different refractive index
becoming transparent. The calcified predentin and process space of the tubule
is known as sclerotic or transparent dentin.
Hardness tests and Roentgen Ray studies indicate these areas to be more
highly mineralized than the other regions of the dentin.
 Sclerotic dentin, because it is characterized physically by increased
transparency with transmitted light, increased hardness and density
and decreases permeability.
Sclerotic dentin is frequently found beneath worn enamel such as occurs
in the incisal area of anterior teeth of the teeth in elderly people.
24

25.  Sclerotic dentin may also be found under slowly progressing caries.
In such cases blocking of the tubules may be considered or defensive
reaction of the dentin, sclerotic dentin is also found beneath tomes
granular layer in the cervical area of older teeth where the cervical
cementum has been exposed to the oral cavity as a result of recession
of the gingival.
CLINICAL IMPORTANCE
The structure of the dentin influences both the pattern of a carious lesion
and the speed which dental caries destroys a tooth; and it accounts for the
sensitivity frequently experienced by patients during the performance of an oral
prophylaxis or during the eating of hot or cold foods.
When at any point the caries process has prevented the enamel as far as
the d.E junction, the carries producing bacteria will also reach this depth and
will come in contact with the peripheral ends of the dentinal tubules.
 Since the bacteria are smaller than the tubular they enter the
tubules. The odontoblastic processes which occupy the tubules are
destroyed, the bacteria travel pulpward in the opened tubules and the
dentin is slowly destroyed.
 Because the bacteria follow the course of the dentinal tubules,
a carious lesion originating around a contact area or in the cervical
25

26. area of a tooth, extends in an apical direction as it approaches the
pulp.
 The horizontal spread of caries is considerably more rapid in
dentin than in enamel. A tooth with only a small area of caries
visible on the surface may be so extensively carious in the dentin the
clinical restoration is impossible.
 The progress of dental caries is often retarded, but not
stopped, by defense reactions that take place in the pulp. One such
reaction is the production of sclerotic dentin. Another defense
reaction against caries is the formation of reparative dentin (at the
location whre the bacteria – filled tubules reach the pulp).
Another characteristic of dentin of particular interest to the dentist is the
location of the “Tomes granular layer” and its effect on the comfort of the
patient.
As we have seen the Tomes granular layer consists of a narrow band of
unmineralized areas in the root dentin immediately beneath the cementum.
 A natural aging process which occurs in nearly all mouths is the gradual
recession of the gingival and a resulting exposure of the cementum at
the necks of the teeth.
In the performance of oral prophylaxis it is necessary to cleans this
exposed cervical cementum. This means working very close to Tomes granular
26

27. layer, which being unmineralized and in close contact with the odontoblastic
processes, causes this area to be very sensitive to hot or cold foods. But after a
few weeks or months, the dentin beneath the exposed surface usually becomes
sclerotic and the patient ceases to notice discomfort.
Dentin Anomalies: Most dentin anomalies such as the dentin dysplasias and
dentinogenesis imperfecta, involve autosomal patterns of inheritance.
It is now understood with some certainty that dentin can respond to
calcium regulating hormones (such as vit D) and adverse changes in serum
calcium levels.
For e.g. patients with parathyroid gland adenomas frequently show a
widened predentin zone and enlarged dentinal tubules.
Both are indicative of dentin resorption and probably demonstrate that
the odontoblasts, active in dentiongenesis throughout life, can function in
dentin resorption as well.
Both dentin resorption and apposition are indicative of dentin
remodeling throughout the life of the tissue.
Dentinogenesis Imperfecta : (Hereditary opalascent dentin)
3 Types:
 Type I – always occurs in association with osteogenesis imperfecta *
deciduous teeth more affected.
27

28.  Type II – This type is not associated with osteogenesis imperfecta unless
by chance * both dentitions are equally affected.
 Type III – (Brandywine type) is a racial isolate and is characterized by
the same clinical appearance as I and II but with multiple pulp exposures
of the deciduous teeth * both dentitions are affected.
 Clinically, they exhibit a characteristic unusual translucent line.
 Because of an abnormal d.E junction, the scalloping is lost  leading to
early loss of enamel by #ing away after which the dentin undergoes
rapid attrition because the teeth are severely flattened.
Radiographically  obliteration of the pulp chambers and root canals by
continud forming of dentin.
In type III, there is a great variability in the deciduous teeth  they
appear as “Shell teeth”, the enamel of the tooth appears normal but the dentin is
extremely thin and the pulp chambers are enormous, this large size of the pulp
chambers is not due to resorption, but rather due to insufficient and deflection
dentin formation.
So, on the radiographs, the teeth appear as shells of enamel and dentin
surrounding extremely large pulp chambers and root canals.
Histologically – Irregular tubules often with areas of uncalcified matrix.
In some areas three may be complete absence of tubules.
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29. [ Treatment – cast metal crowns on posterior teeth and J. C. on anterior
teeth, fillings are not usually permanent because the dentin is soft].
CONCLUSION
There is a proverb that what the mind doesn’t know, the eyes cannot see.
So, not only is it necessary to know, but also to understand and apply the
knowledge of dentin to the myriad applications of dentistry so as to achieve a
more holistic and fulfilling therapeutic goal and ultimately satisfied individuals
both the clinician as well as the patient.
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