Presented by

Saloni Pathak

(pg 1st yr.)Department of Conservative Dentistry and

Endodontics

Jaipur dental college

INTRODUCTION PHYSICAL AND CHEMICAL PROPERTIES DEVELOPMENT AND MINERALIZATION HISTOLOGY OF DENTIN STRUCTURAL LINES TYPES OF DENTIN AGE AND FUNCTIONAL CHANGES

Also called Substantia Eburnea.

Forms the main bulk and general form of the tooth.

Covered by enamel in crown and by cementum in root.

Determines the shape of the crown and the number and size of the roots.

It has tubules throught its thickness which are given off by odontoblasts.

Colour : light yellow-decidious dentition

pale yellow – permanent dentition

Hardness : less harder than enamel , more harder

than bone and cementum.

It is viscoelastic and subject to slight deformation.

More radiolucent than enamel.

Thickness : 3 to 3.5mm in coronal aspect.

Density 22.1gm/mm

KHN 68

Reflective index 1.54

Specific gravity 2.3

CHEMICAL PROPERTIESTencate has reported that :-

According to weight

According to volume

Inorganic 70%

Organic 20%

Water 10%

Inorganic 45%

Organic 33%

Water 22%

Organic components

Collagen fibrils embedded in the ground substance of mucopolysaccharides.

collagen fibers (82%)

ground substance (18%)

It consist of mainly type 1 collagen and type 3and type 5 collagen in small amount.

Lipids

Growth factors

Serum proteins

Constituents of Ground substance :-

Proteoglycans – Condroitin sulphates

Decorin

Biglycan

Glycoproteins – Dentin sialoprotein (DSP)

Osteonectin

Osteopontin

Phosphoproteins – Dentin phosphoprotein(DPP)

γ-carboxyglutamate

Inorganic components

Consist of hydroxyapatite crystals –plate

shaped.

Much smaller than crystals of enamel.

These crystals are calcium rich and carbon poor.

DIMENSIONS :-

length 60-70nm

width 20-30 nm

thickness 3-4nm

Dentin also contains small amount of sulfates, phosphates ,carbonates.

Development is divided into four stages:

1)Bud stage2)Cap Stage3)Early bell Stage4)Late bell stage

Dentin is formed by cells called odontoblasts, which

differentiate from ectomesenchymal cells of dental

papilla. Thus the dental papilla is the formative organ of

dentin and eventually becomes the pulp of the tooth.

Dentinogenesis is a 2 stage or phase sequence in

which the collagen matrix is formed first and then

calcified. Von Korff’s fibers described that the initial

deposition begins at the cusp tips after odontoblast

differentiation.

STAGES OF DENTINOGENESIS

Odontoblasts differentiation

Collagen matrix formation

Mineralization of matrix

Odontoblast differentiation

UndifferentiatedMesenchymal cell

mitotic spindle perpendicular to basal lamina

Epithelial cell

Inner enamel epithelium

Under the influence of epithelium start differentiating

odontoblast

subodontoblast

Odontoblast differentiate , change from ovoid to columnar shape and nuclie get basally oriented.

One or several processes arrises from the apical end of cells in contact with basal lamina.

length increases to 40 microns and constant width 7 microns.

Proline appears in rough endoplasmic reticulum and golgi apparatus.

Cell recedes leaving behind a single extension.

As matrix formation continues, odontoblastic process

lengthens.

Initially 4 microns of dentin is formed daily till the crown

is formed and erupt into occlusion. after this it reduces to

1 microns.

Occurs by globular calcification.

Deposition of very fine plates of hydroxyapatite on the surface of collagen fibrils and ground substance.

Starts from common centre, so called spherulite form. These are first form of dentin.

Long axis of crystals are parallel to long axis of fibrils.

Important factors in mineralization are :-

Odontoblast secret dentin phosphoprotein (DPP) :-

it is highly ionic and binds to the minrelization front and

controls the growth of apatite crystals.

Osteopontin :- promotes mineralization.

Osteonectin :- inhibits the growth of apatite crystals

and promotes its binding to collagen.

Gamma carboxyglutamic acid (GLA) protein :- attract

the calcium.

Genes implicated in dentinogenesis :-

PHEX – for mineralization

MAP1B – for odontoblast differentiation.

When viewed microscopically following structural features can be identified

Dentinal Tubules Peritubular Dentin Intertubular Dentin Predentin Odontoblastic processes Interglobular Dentin

Granular layer of Tomes Dentinoenamel junction

House the major cell processes of odontoblast.

Occupy 20 to 30 % volume of intact dentin.

Follow a gentle S- curve which runs

perpendicular from pulp to periphery

called Primary Curvature.

Along the entire lengths, exhibit

minute secondary curvatures that are

sinusoidal in shape.

In the root, incisal edge and cusp tip

tubules are almost straight.

A – S- shaped TUBULEB- DEJ C- MANTLE DENTIND- PRIMARY DENTIN

Terminal branches

Tubules are longer than the thickness of dentin.

Ratio of outer and inner surface dentin is 5:1.

No. of tubules/unit area on pulpal and outer dentin is 4:1.

Diameter is larger at the pulpal side (1.5-3 mm) than at the periphery(1mm).

Tubules/unit area in crown is more than in root.

Tubules are farther apart in peripheral layer and

more closely packed near the pulp.

No. of dentinal tubules decreases with age, thus

reducing sensitivity.

The dentinal tubules have lateral braches

throughout dentin, called

Canaliculi / microtubules,1 um in

diameter.

They originate at right angles to the

main tubule at every 1-2 um along

its length.

Some may enter adjacent tubules

while others end in intertubular dentin.

Thus form anastomosing canalicular system.

MICROTUBULE

Few dentinal tubules that extend through the DEJ in enamel

for several mm are called enamel spindle.

A – ENAMEL SPINDLEB – DENTINAL TUBULE

Dentinaltubules

Dentinal Tubules

Coronal dentin

Root dentin

Immediately surrounds the dentinal tubules, highly calcified

matrix and forms the walls of tubules .

Highly mineralized , harder, provide added structural

support for intertubular dentin , thus strengthening the

tooth.

It is twice as thick in outer dentin (750nm) than inner

dentin(44nm).

Contains few collagen fibrils and higher proportion of

sulphated proteoglycans.

With the formation of peritubular dentin, there is a reduction in diameter of the process near DEJ

Due to its decreased collage content, dissolves more quickly in acid.

Rich in proteins like dentin sialoprotein.

After decalcification the processes appear to be surrounded by empty space.

Having an inner organic lining called Lamina limitans, consist of glycosaminoglycans (GAG)

A – INTERTUBULAR DENTIN

B – PERITUBULAR DENTIN

C – DENTINAL TUBULE

Located between the dentinal tubules or in other

terms between the zone of peritubular dentin.

Constitute main bulk of dentin.

Although highly mineralized, it is retained after

decalcification.

Its organic matrix consists mainly of interwoven network

of collagen fibrils having diameter of 50-200 um in which

apatite crystals are deposited. Fibrils are arranged

randomly at right angles to dentinal tubules.

Dentinal tubules

Peritubular dentin Intertubular dentin

First formed dentin.

Not mineralized.

Located adjacent to pulp tissue, 2-6 micron

wide.

Its thickness remains constant.

As the collagen fibers undergo mineralization at

the predentin- dentin junction, the predentin

becomes dentin & new layer of predentin forms

circumpulpally .

Thickest during dentinogenesis and diminishes

with age.

This predentin layer, secreted by odontoblasts, is

a protein carbohydrate complex consisting of

proteoglycans , phosphoproteins, glycoproteins

and collagen fibrils.

Its presence is important to maintain the integrity

of dentin.

Zone of hypomineralisation present between the mineralized globules which have failed to coalease into a homogenous mass.

Defect of mineralization & not of matrix formation.

It is seen in teeth with vitamin D deficiency or exposure of high level of floride during dentinogenesis , hypophosphatasia.

Shows higher concentration of sulfur.

It is seen in circumpulpal dentin just below mantle dentin. It follows incremental pattern.

Interglobuler Dentin

Inter-globulerdentin

DentinalTubules

DentinoEnamelJunction

Inter-globulerdentin

Cytoplasmic extensions of odontoblast cells.

The odontoblast cells lie in the peripheral pulp at the pulp- predentin border & their process extend into the dentinal tubules.

Diameter: 7 um

Length :- 40 um

Diameter largest near pulp (3-4 um) and tapers approx. 1 um in dentin

Odontoblasts and process

Odontoblast cellsOdontoblast process

Dentin Pulp

The processes narrow to about half the size of the cell as they enter the tubules

The processes is composed of microtubules of 20 micron in diameter & small filaments 5 – 7.5 micron in diameter

Divide near the DEJ & extend into the enamel as enamel spindles

Junction b/w enamel and dentin is called DEJ.

Irregular and scalloped.

Convexity of scallops are directed towards dentin and concavity towards enamel.

A membrane is seen b/w the enamel and dentin during tooth development called membrane performativa. After calcification this membrane disappers and the interface is called DEJ.

A ground section of root, when viewed under transmitted

light , a zone adjacent to the cementum appears

granular.This is called Tome’s Granular Layer.

This zone increases in amount from cementoenamel

junction to the root apex.

Appears dark in transmitted light and lighter in reflected

light.

Remain unmineralized.

Shows higher concentration of calcium and

phosphorous.

This granular layer represent the looped terminal

portions of the dentinal tubules in the root dentin.

Dentin

Cementum

Granular layer of Tomes

Formed prior to the root completion and eruption of teeth.

MANTLE DENIN –

First formed dentin in the crown underlying DEJ.

It is the outermost part of the primary dentin & is 20 -150 microm thick .

Bounded by DEJ & zone of interglobular dentin .

It consist of lager collagen fibers (type 3).

Less mineralized.

CIRCUMPULPAL DENTIN –

Forms remaining primary Dentin or bulk of tooth

Represents all Dentin formed before root completion.

Collagen fibrils are smaller in diameter 0.05 micron & are more closely packed than mantle dentin .

More mineral content than mantle dentin .

Narrow band of dentin bordering the pulp and

formed after the root completion and complete

eruption of teeth.

Continues to forms throughout the life of the tooth.

Contains fewer tubules than primary dentin.

Formed more slowly than primary dentin.

At the junction of primary and secondary

dentin a bend is seen in the dentinal tubules.

It is not formed uniformly and appears in greater amount on root and floor of the coronal pulp chambers , where it protects the pulp from exposure in older teeth.

Due to the regular arrangement of dentinal tubules, it is called regular sec.dentin.

With the growth of this dentin there is decrease in size of the pulp chamber with age. So called pulp recession.

Tubules of Secondary Dentin scleroses more rapidly than those of the Primary Dentin. Thus reduce overall permeability of dentin thereby protecting the pulp.

Primaryphysiologicaldentin

Secondaryphysiologicaldentin

Also referred as reparative dentin, response dentin,

irregular secondary dentin.

It is localized formation of Dentin on pulp dentin border ,

formed in reaction to trauma such as caries or

restorative procedures, attrition ,abrasion , erosion.

Formations depends on the intensity & duration of

stimulus.

Forms along entire pulp dentin border by cells directly

affected by the stimuli.

Tertiary dentin may have tubules continous with those of

sec. dentin , tubule spares in no. and irregurarly

arranged or no tubules at all.

This minimizes dentin permeability at the site of

deposition thus giving protection to the underlying dental

pulp.

It help seal off the area of injury causing resolution of

inflammation .

The cells forming tertiary dentin become included in the

dentin , and hence called Osteodentin.

Primaryphysiologicaldentin

Secondaryphysiologicaldentin

Tertiarydentin

Primaryphysiologicaldentin

Secondaryphysiologicaldentin

Tertiarydentin

Dead tracts

Tertiary dentin is further classified into :-

• Reactionary dentin /Regenerated dentin

• Reparative dentin

By trauma stimuli odontoblast processes are exposed , cut/killed ,die or survive.

Those cells who survived – produce dentin called Reactionary/Regenerated dentin.

Those who are killed – are replaced by the migration of undifferentiated cells from the cell rich zone or undifferentiated perivascularcells present deeper inside the pulp.

The newely differentiated odontoblast than begin deposition of Reparative dentin

This action to seal off the zone of injury occurs as a healing process initiated by the pulp, resulting in resolution of the inflammatory process and removal of dead cells.

This zone of hard tissue thus formed is called Reparative Dentin.

Due to the irregular nature of dentinal tubules , these type of dentin is called irregular sec. dentin.

Tertiary dentin is differ from other form of dentin, as it contains dentin phosphophoryn.

Incremental lines of Von Ebner

Contour lines of Owen

Neonatal lines

They appear as fine lines or striations in dentin .

They run at right angles to the dentinal tubules.

These lines reflects daily rhythmic, recurrent deposition of dentin matrix in the daily formative process .

Distance between lines varies from 4 –8 micron in the crown to much less in the root .

Daily increment decreases as the tooth comes into functional occlusion.

Incremental line of von Ebner

Some of the incremental lines are accentuated because

of disturbances in the matrix & mineralization process

,these are called contour lines of Owen.

They lie at right angle

to the von ebner lines.

These lines represents

hypocalcified bands.

DentinEnamel

Lines ofOwen

Dentino-enamel Junction

In deciduous teeth & in first permanent molars, where dentin is formed partly before & partly after the birth, the prenatal & post natal dentin separated by accentuated contour line

Seen in enamel as well as dentin.

The line represents the disturbances in mineralization due to the abrupt changes in environment that occurs at birth.

It is a zone of hypocalcification.

The dentin matrix formed prior to birth is better quality than that formed after birth.

NEONATAL LINE IN ENAMEL

NEONATAL LINE IN DENTIN

Formation of secondary dentin

Formation of reperative dentin

Dead tracts

Sclerotic dentin

The presence of caries , attrision , abrasion , erosion, cavity preparation or any external stimuli may cause increase in dentin deposition as well as increase in mineralization of old existing dentin.

Which leads to excessive formation of collagen fibers and appatite crystals in dentinal tubules.

That leads to complete obliteration of dentinal tubules as a defensive reaction of dentin.

Apatite crystals are initially only sporadic in a dentinal tubules but gradually the tubule becomes fluid with a fine meshwork of crystals.

Gradually tubule lumen is obliterated with mineral, which appears very much like Peritubular dentin.

Due to the high mineral content, they appear

transparent.

Sclerotic dentin is observed in teeth of elderly people,

specially roots , also observed under slowly progressing

caries.

Sclerosis reduces the permeability of dentin & help to

prolong pulp vitality.

Appears dark in reflected light and transparent in

transmitted dentin.

Dentin formed due to aging is harder than that formed

below carious lesion.

It is harder than normal dentin and fracture toughness is

reduced, elastic properties are altered.

Crystals present in this dentin are smaller than those

present in normal dentin.

Dental cariesSclerotic dentin

In ground section of dentin, when viewed under transmitted light shows sometimes dark lines that follow the course of dentinal tubules.These are called Dead Tracts.

They are dead degenerated odontoblast processes in dentinal tubules.

These tubules are empty and are filled with air and that appears dark in transmitted light.

Occur in condition such as attrision , erosion, abrasion, cavity preperation.

It is often observed in areas of narrow pulp horn because of crowding of odontoblasts.

Appears greater in extent in older teeth due to aging

process. These areas demonstrate decreased

sensitivity.

They are probably the initial step in formation of sclerotic

dentin.

A – DEAD TRACTS

B – SECONDARY DENTIN

C – TERTIARY DENTIN