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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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

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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.

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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.

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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

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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.

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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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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 m.

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.

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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.

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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

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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.).

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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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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.

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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).

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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.

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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.

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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.

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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.

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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.

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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.

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Intertubular Nerves: Dentinal tubules contain numerous nerve endings in the

pre-dentin and inner dentin no farther than 100-150 m 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.

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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.

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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.

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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.

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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

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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

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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.

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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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[ 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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