DENTIN

DENTIN – COMPOSITION, FORMATION, AND STRUCTURES

DENTINOGENESIS

ORIGIN OF THE DENTIN

Dentin is formed by cells called odontoblasts that defferentiated from ectomesenchymal cells of the dental papilla following an organizing influence that emanats from the inner dental epithelium.

Thus the dental papilla is the formative organ of dentin and eventually becomes the pulp of the tooth.

For dentinogenesis and amelogenesis to take place normally, the differentiating odontoblasts and ameloblasts will receive signals form each other –“reciprocal induction”.

CELLS RESPONSIBLE FOR DENTINOGENESIS

There are two types of cells involved in dentin formation - odontoblasts and sub odontoblasts (fibroblasts).

Start of dentinogenesis begins after the final differentiation of the odontoblasts and subodontoblasts.

STAGES OF APPOSITION

1. Elongation of inner enamel epithelium;

2. Differentiation of odontoblasts;

3. Formation of dentin;

4. Formation of enamel.

PREPARATION FOR THE FORMATION OF TOOTH STRUCTURESContinued growth of the tooth germ leads to bell stage, where the enamel organ resembles a bell with deepening of the epithelium over the dental papilla;

Continuation of histodifferentiation(ameloblasts and odontoblasts are defined)

and beginning of morphodifferentiation(tooth crown assumes its final shape).

START OF DENTINOGENESIS

- Begins after the final differentiation of the odontoblats and subodontoblasts;

- Odontoblasts extended theire processes;

- Released space under the basement membrane;

- The first free space is in the growth center.

ENAMEL ORGAN AND DENTAL PAPILLA

The cells of inner dental epithelium exert an organizing influence on the underlying mesenchymal cells in the dental papilla, which later differentiate into odontoblasts;

Outer dental epithelium - cuboidalcells that have a function to organize a network of capillaries that will bring nutrition to the ameloblasts.

DENTAL PAPILLA AND PREODONTOBLASTS Before the inner dental epithelium begins to produce enamel, the peripheral cells of the mesenchymal dental papilla differentiate into odontoblasts under the organizing influence of the epithelium;

First, they assume a cuboidal shape;

The basement membrane that separates the enamel organ and the dental papilla just prior to dentin formation is called the “membrana preformativa”.

preodontoblasts

Membrana

preformativa

ODONTOBLASTS DIFFERENTIATIONIt is brought about by the expression of signaling molecules and growth factors in the cells of the inner epithelium;

a.The dental papilla cells are small and undifferentiated and exhibit a central nucleus and few organelles;

At this time they are separated from inner epithelium by an acellular zone that contains some fine collagen fibrils;

b. Committed dental ectomesenchymal cells that are in a state of mitosis or cell division;

c. Daughter cells that are competent to become odontoblasts remain in the peripheral zone;

d. Differentiated odontoblasts with a polarized nucleus and citoplasmicextentions;

Preodontoblast;

Undifferentiated cell;

Basement membrane;

4 and 5 - subodontoblastic cells.

PREODONTOBLASTSA -preodontoblasts;

В – preameloblasts;

С –basement membrane;

With the begining of the production of dentin it becomes in dentinoenamel junction;

Differentiation of odontoblasts is mediated by expression of signaling molecules and growth factors in the inner dental epithelial cells.

ACELLULAR ZONE

This zone gradually is eliminated as the odontoblasts differentiate and increase in size and occupy this zone;

They are characterized by being highly polarized, with their nuclei positioned away from the inner dental epithelium

Acellularzone

DIFFERENTIATION OF ECTOMESENCHYMAL CELLS OF DENTAL PAPILLA TO PREODONTOBLASTS

Almost immediately after cells of the inner dental epithelium reverse polarity, changes also occur in the adjacent dental papilla;

Ectomesenchymal cells rapidly enlarge and elongate to become preodontoblasts first and then odontoblasts as their cytoplasm increases in volume to contain increasing amount of protein-synthesizing organelles.

Short columnar cells bordering the dental

papilla – inner dental epithelium will

eventually become ameloblasts ;

5. The odontoblasts as they differentiate will start elaborating organic matrix of dentin,

which will mineralize.

6. As the organic matrix of dentin is deposited, the odontoblasts move towards the

center of the dental papilla, leaving behind cytoplasmic extensions which will soon be

surrounded by dentin;

7. Therefore, a tubular structure of dentin is formed.

The odontoblasts appear like protein-producing cells;

DIFFERENTIATION OF ODONTOBLASTS

ODONTOBLASTS AND SUBODONTOBLASTS

odontoblasts

Subodontoblasts

Dentin formation

proceeds toward the

inside of the tooth;

ODONTOBLASTS

А – nucleus;

В - secretory end;

С - secreted matrix.

They are the dentin-forming cells, differentiate from cells of the dental papilla;

They begin secreting an organic matrix around the area directly adjacent to the inner enamel epithelium, closest to the area of the future cusp of a tooth;

ODONTOBLAST PROCESSOR TOMES`FIBER

The odontoblast develops a cell process, the odontoblast process, which is left behind in the forming dentin matrix;

The organic matrix contains collagen fibers with large diameters (0.1–0.2 μmin diameter);

The odontoblasts begin to move toward the center of the tooth, forming an extension called the odontoblast process;

ODONTOBLASTS - LARGE PEAR-SHAPED CELLS

Thus, dentin formation proceeds toward the inside of the tooth;

The odontoblast process causes the secretion of hydroxyapatitecrystals and mineralization of the matrix.

DENTINAL TUBULES FORMATION

As the odontoblastic process elongates, a dentinal tubule is maintained in the dentin, and the matrix is formed around this tubule;

THE BEGINNING OF DENTINAL DEPOSITION

ODONTOBLASTS PROCESSESThe plasma membrane of odontoblasts adjacent to inner epithelium extend stubby processes into the forming extracellular matrix;

On occasion one of these processes may penetrate the basal lamina and interpose itself between the cells of inner epithelium to form what later becomes an enamel spindles;

MATRIX VESICLES

As the odontoblasts form these processes, it also buds off a number of small, mambrane-bound vesicles known as matrix vesicles, which come to lie superficially near the basement membrane.

This area of mineralization is known as mantle dentin and is a layer usually about 150 μm thick.

ODONTOBLAST BRANCHING GROWTHS ON THE PERIPHERY OF THE DENTIN

STAGES OF DENINOGENESIS

Formation of organic matrix:

Fibrogenesis;

Maturation of the organic matrix;

Mineralization of the matrix.

2 STEPS OF DENTINOGENESIS

Odontoblasts with cytoplasmicprocesses forming dentinal tubules;

1. Formation of collagen matrix;

2. Deposition of calcium and phosphate

(hydroxyapatite) crystals in the matrix.

Fibrillogenesis

During fibrillogenesis are formed two kinds of fibers

Von Korff`s fibers or α-fibers - thick collagen fibers perpendicular to the dentin-enamel border are formed by subodontoblasts;

Odontoblasts are forming thin collagen fibers perpendicular to the Korff`s fibers – β-fibers.

SYNTHESIS OF COLLAGEN AND ITS ARANGEMENT IN FIBRILS AND FIBERS

The collagens in dentin are primerytype I with trace amounts of type V collagen and some type I collagen trimer;

The type I collagen is a key structural component of dentin matrix.

Some types (of 15) of known collagen

Type Molecular Tissue distribution

Fibril-forming I [a1(I)]2 a2(I) bone, skin, tendon, ligaments

(90%) of body collagen

II [a1(II)]3 cartilage, intervertebral disc,

notochord, vitreous humor of eye

III [a1(III)]3 skin, blood vessels, internal organs

V [a1(V]2 a2(V) as type I

XI [a1(XI] a2(XI) a3(XI) as type II

Fibril-associated IX [a1(IX] a2(IX) a3(IX) cartilage (with type II)

XII [a1(XII)]3 tendon, ligaments (with some type I)

Network-forming IV [a1(IV)]2 a2(IV) basal laminae

VII [a1(VII)]3 anchoring fibrils beneath stratified

squmous epithelia

Some of the fifteen known types of collagen

KORFF`S FIBERSFORMATION

Korff's fibers (corkscrew fibers) passing between odontoblasts and reach

predentin.

The question of the origin of these fibers is controversial.

KORFF'S FIBERS

The first sign of dentin formation is the appearance of distinct, large-diameter collagen fibrils;

They are 0,1 to 0,2 µm in diameter and called von Korff'sfibers;

They originate deep among the odontoblasts, extend toward the inner epithelium, and fan out in the structurless ground substance immediately bellow the epithelium.

FORMATION OF THE FIRST LAYER OF THE DENTIN – THE MANTLE DENTIN

The next step in the production of dentin is formation of its organic matrix;

Odontoblasts differentiate in the preexisting ground substance of the dental papilla;

The first dentin collagen syntesized by them is deposited inthis groun substance.

Layer of polarized odontoblastswith Tomes' fibers.

VON KORFF`S FIBERS APPEAR AS CONVOLUTED, THREADLIKE STRUCTURES THAT ORIGINATED DEEP BETWEEN ODONTOBLASTS

Following differentiation of odontoblasts, first layer of dentin is produced, characterized by appearance of large-diameter type III collagen fibrils (0.1 to 0.2 μmin dia) called von Korff’s fibers, followed by type I collagen fibers.

Odontoblasts and nerve endsbetween them.

Odontoblasts and corkscrew fibers (Korff's fibers)

NONCOLLAGENOUS PROTEINS

The other group of proteins is the noncollagenousproteins;

They are grouped into five categories;

The first and likely the most important group –two proteins, originally classified as dentin-specific:

DPP – dentin phosphoprotein;

DSP – dentin sialoprotein;

After type I collagen, DPP is most abundant of dentin matrix proteins and represent almost 50% of the dentin ECM.

DPP

DPP has a high affinity for type I collagen as well as calcium and protein for initiation of dentin mineralization and is therefore considered a key protein for the initiation of mineralization;

DPP may also affect the shape and size of apatite crystals.

DSP

DSP accounts for 5% to 8% of the dentin matrix;

DSP played a role in cell attachment;

A SECOND CATEGORY OF NONCOLLAGENOUSPROTEINS

Osteocalcin;

Bone sialoprotein;

They are classified as mineralized tissue-spacific, because they are found in all the calciffiedconnective tissies.

A THIRD GROUP OF NONCOLLAGENOUSPROTEINS

They are sinthesized by odontoblasts;

They are:

Osteopontin;

Osteonectin.

PREDENTINNewly secreted dentin is unmineralized and is called predentin;

It is easily identified in haematoxylin and eosin stained section since it stains less intensely then dentin;

It is usually 10-47 micrometers and lines the innermost region of the dentin;

It is unmineralized and consists of collagen, glycoproteins and proteoglycans;

It is similar to osteoid in bone and is thickest when dentinogenesis is occurring.

MANTLE PREDENTINAs the odontoblasts continue to increase in size, they also produce smaller collagen type I fibrils that orient themselves parallel to the future dentinoenamel junction;

In this way a layer of mantel predentin appears.

THE FIRST STAGE IS FORMATION OF MANTLE DENTIN:

Its means the deposition of matrix which is composed of collagen fibers in a ground substance rich in glycosaminoglycans.

The fibers known as Von Korff`s fibers are argyrophilic.

Subodontoblasts may be responsible for a proportion of the very first matrix including the von Korff`s fibers.

Odontoblasts form the major part of mantle dentin matrix.

PRYMARY DENTIN

Whereas mantle dentin forms from the preexisting groundsubstance of the dental papilla, primary dentin forms through adifferent process;

Odontoblasts increase in size, eliminating the availability of anyextracellular resources to contribute to an organic matrix formineralization;

Additionally, the larger odontoblasts cause collagen to besecreted in smaller amounts, which results in more tightlyarranged, heterogeneous nucleation that is used formineralization;

Other materials (such as lipids, phosphoproteins, andphospholipids) are also secreted.

MINERALIZED DENTINE MATRIX

FIRST LOYER OF MANTLE DENTIN

CELLULAR ACTIVITY IN THE GERM CENTERS

ODONTOBLASTS AND SUBODONTOBLASTS

MINERALIZATION

The mineral phase first appears within the matrix vesicles as single crystals believed to be seeded by phospholipids present in the vesicle membrane;

The crystals grow rapidly and rupture from the confines if the vesicle to spread as a cluster of crystallites that fuse with adjacent clusters to form a continuous layer of mineralized matrix.

EARLY MINERALIZATION OF THEDENTIN MATRIX

NEW FREE SPACE EXEMPTED FROM THE ODONTOBLASTS FOR A NEW LAYER OF DENTIN

PATTERN OF MINERALIZATION

Two patterns of mineralization can be observed, that seems to depend on the rate of dentin formation:Globular calcification;

Linear calcification.

GLOBULAR MINERALIZATION

It involves the deposition of crystals in several discrete areas of matrix by heterogeneous capture in collagen;

With continued crystal enlarge and eventually fuse to form a single calcified mass;

The pattern of mineralization is best seen in the mineralization foci that grow and coalesce;

MINERALIZATION IN CIRCUMPULPAL DENTIN

It can progress in a globular or linear pattern;

The size of the globules seems to depend on the rate of dentin deposition:When the rate of deposition is fastest, with largest globules occurring;

When the rate of formation progresses slowly, the mineralization front appears none uniform and the process is said to be linear.

odontoblast

Subodonto-blast

predentin

Vast zone

THE TWO DIRECTION OF DENTIN FORMATION –SPREADS DOWN THE CUSP SLOPE AS FAR AS CERVICALLOOP, AND DENTIN THICKENES

A – ODONTOBLASTS; B- PREDNTIN; C –AMELOBLASTS; D – ENAMEL; E – PREDNTIN.

VASCULAR SUPPLY OF THE ODONTOBLASTS

LIFE CYCLE OF ODONTOBLASTS

There are only 3 stages in the life cycle of odontoblasts:

1. Differentiating stage;

2. Formation stage;

3. Quiescent stage.

DIFFERENTIATING STAGE

FORMATIVE STAGE:

Concentration of the cell organelles, granular components and globular elements;

Production of the first amount of dentin (dentin matrix);

The odontoblasts retreat from the basement membrane;

Leaving a single process which become enclosed in the dentinal tubule (tomes fiber;.

With successive deposition of dentin, tubule and process grow in length.

QUIESCENT STAGE:

Actively secreting odontoblasts decrease slightly in size.

The odontoblastic process stop to elongate;

In this stage the odontoblasts produce only secondary dentin.

STAGES OF DENTIN FORMATION AND TYPES OF DENTIN

Dentin is formed throughout

the life of the tooth if the

tooth pulp is alive

А – ОDONTOBLASTS; В – PREDENTIN; C – DENTAL PULP; D –DENTIN.

PRIMARY DENTINPrimary dentin, the most prominent dentin in the tooth, lies between the enamel and the pulp chamber;

The outer layer closest to enamel is known as mantle dentin. This layer is unique to the rest of primary dentin;

Mantle dentin is formed by newly differentiated odontoblasts and forms a layer approximately 150 micrometers wide. It is a more mineralized dentin;

Below it lies the circumpulpal dentin, a less mineralized dentin which makes up most of the dentin layer and is secreted after the mantle dentin by the odontoblasts.

PREDENTIN, DENTIN, ODONTOBLASTS

Predentin

Dentin

Dentinal

tubulesOdontoblasts

SECONDARY AND TERTIARY DENTIN

Secondary dentin is formed after root formation is finished and occurs at a much slower rate. It is not formed at a uniform rate along the tooth, but instead forms faster along sections closer to the crown of a tooth;

This development continues throughout life and accounts for the smaller areas of pulp found in older individuals;

Tertiary dentin, also known as reparative dentin, forms in reaction to stimuli, such as attrition or dental caries.

DENTINOGENESIS; PRIMARY DENTIN; SECONDARY DENTIN;

SECONDARY DENTIN (REGULAR SECONDARY DENTIN)

Secondary dentin is formed after root formation is complete, normally after the tooth has erupted and is functional. It grows much slower than primary dentin, but maintains its incremental aspect of growth ;

It has a similar structure to primary dentin, although its deposition is not always even around the pulp chamber. It is the growth of this dentin that causes the decrease in the size of the pulp chamber with age.

TERTIARY DENTIN (IRREGULAR SECONDARY DENTIN OR REPARATIVE DENTIN)

Tertiary dentin is dentin formed as a reaction to external insult such as caries. It is of two types: reactionary, where dentin is formed from a pre-existing odontoblast;

or reparative, where newly differentiated odontoblast-like cells are formed due to the death of the original odontoblasts, from a pulpal progenitor cells.

Tertiary dentin is only formed by an odontoblast directly affected by stimulus.

Tertiary dentin.

COMPOSITION OF DENTIN

Organic substance:

30-25% from its weight;

About 90% collagen fibers:

About 10% ground substance:

Inorganic substance:

70-75% from its weight:

Hydroxyapatite crystallites.

PROPERTIES OF DENTIN

Yellowish in color;

Elastic;

Less hard than enamel, but more than cementum;

Less radio-opaque than enamel, but more than cementum;

3-10 mm thick.

DENTINDentin is a calcified tissue of the body, and along with enamel, cementum, and pulp is one of the four major components of teeth.

Usually, it is covered by enamel on the crown and cementum on the root and surrounds the entire pulp.

By weight, 70% of dentin consists of the mineral hydroxylapatite, 20% is organic material and 10% is water;

Yellow in appearance, it greatly affects the color of a tooth due to the translucency of enamel;

Dentin, which is less mineralized and less brittle than enamel, is necessary for the support of enamel.

TYPES OF DENTIN

Mantle dentin;

Interglobular dentin;

Circumpulpal dentin;

Predentin.

MANTLE DENTIN

The most superficial layer of dentin;

The most highly mineralized;This is due to:

Predominance of Korff`s fibers;

They are properly arranged in parallel;

This helps in tightly arrangement of crystals;

There are at least intercrystal spaces;

There are at least organic matter.

MANTLE DENTIN

The most highly mineralized dentin;

It is similar in degree of mineralization of enamel;

MANTLE DENTIN

It is situated just below thedentinoenamel junction;

There odonto-blast processes lose their curve.

BRANCHES OF ODONTOBLASTS

At DEJ odontoblasts branch out;

In the lower sections of dentin, they are united in one main branch;

On the surface, go out a greater number of processes than leave from the pulp.

CURVATURE OF THE DENTINAL TUBULESA – neonatale line;

B – Mantle dentin;

C – circumpulpal dentin;

D - S-shaped primary curvateure of the dentinal tubules in human crown dentin;

E – DEJ.

S-SHAPED CURVETURE OF THEDENTINAL TUBULES

A. S-shaped path curveture of the dental tubules;

B. DEJ;

C. Mantle dentin;

D. Circumpulpal dentin.

DENTINAL TUBULES

A. Odontoblasts in the dentinal tubules;

B. DEJ;

C. Enamel;

D. Spindles in the enamel

SPINDLES IN THE ENAMEL

During histogenesis,part of processes were passed the DEJ to stimulate ameloblasts.

MANTLE DENTIN

CIRCUMPULPAL DENTIN

It is the thickest layer of dentin;

It is less mineralized than mantle dentin; The collagen fibers of this dentin are thinner than mantle dentin -β-fibers;

The Korff`s fibers (α- fibers) are less;

The crystals are arranged along the fibers;

They are chaotically arranged and have higher intercrystal spaces.

CIRCUMPULPAL DENTIN

Dentinal tubules with odontoblast`s processes;

ODONTOBLAST PROCESSES IN TUBULES WITH NUMEROUS LATERAL BRANCHES.

LATERAL BRANCHES OF THE ODONTOBLAST PROCESSES

Longitudinal crosssection of the dentin;

Dental tubules;

Lateral branches of the odontoblasts.

Dental tubules afterdemineralization

INTERGLOBULAR DENTINIt is the term used to describe areas of hypomineralized dentin where globular zones of mineralization (calcospherites) have failed to fuse into a homogeneous mass within mature dentin;

It is seen in the circumpulpal dentin just below the mantle dentin;

It is a defect of mineralization and not of matrix formation;

The normal architectural pattern of the tubules remains unchanged, and they run uninterrupted through the interglobular areas.

INTERGLOBULAR DENTIN

D. Circumpulpal dentin;

Igd – interglobular dentin;

e – enamel.

HYPOMINERALIZED AREASBETWEEN THE GLOBULES, TERMEDINTERGLOBULARE SPACES

INTERGLOBULARE SPACES

GREATER INCREASE

GLOBULES OF MINERALIZATIONGlobular appearance of the mineralization in dentin arising from fusion of globules of hydroxyapatite or calcospherites.

GRANULAR LAYER OF TOMESWhen a section of root is studied, a granular-appearing layer of dentin is seen underlying the cementum that covers the root;

This layer is known as the granular layer of Tomes;

This layer is prevalent when the person has had a deficiency in vitamin D;

This layer is most frequently found in the first permanent molars.

Dentinal tubules in different layers of dentin

Dental tubules ininterglobular dentin

Dental tubules in circumpulpaldentin

GRANULAR LAYER OF TOMES

PREDENTINIt is a band of newly formed, unmineralized matrix of dentin at the pulpal border of the dentin;

Predentin is evidence that dentin forms in two stages: First – the organic matrix is deposited;

Second – an inorganic mineral substance is added;

During primary dentin formation, 4µm of predentin is deposited and calcified each day;

After occlusion and function, this activity decreases to 1.0 to 1.5 µm per day;

PREDENTIN

A – Odontoblasts in the pulp;

B - Predentin;

C- Dental pulp;

D - Dentin

В – PREDENTIN; С –THE BOUNDARY OF MINERALIZATION WITH A GLOBULS OF MINERALIZATION.

PREDENTIN

INCREMENTAL LINES All dentin is deposited incrementally, which means

that as a certain amount of matrix is deposited daily, a hesitation in activity follows;

This hesitation in formation results in an alterationof the matrix known as incremental lines, or lines of von Ebner;

Prenatal dentin and postnatal dentin are separated by an accentuated contour line known as the neonatal line and reflects the disturbance in mineralization created by the physiological trauma of birth.

COUNTOUR LINES OF OWEN (А)

Another type of incremental pattern found in dentin is the contour lines of Owen;

They are known as caused by accentuated deficiencies in mineralization;

These are recognized in longitudinal ground sections;

INCREMENTAL LINES, OR LINES OF VON EBNER;

This incremental lines run at right angles to dentinal tubules and generally mark the normal rhythmic, linear pattern of dentin deposition;

The 5-day increment can be seen readily in conventional and ground sections, situated about 20µm apart.

HISTOLOGY OF DENTIN

When the dentin is viewed microscopically, several structural features can be identified: Dentinal tubules;

Peritubular dentin;

Intertubular dentin.

LONGITUDINAL GROUND SECTION OF DENTIN

(A) – Intertubulardentin

(B) – peritubulardentin;

Odontoblastprocesses incanalicules, calledtubules (C).

Each odontoblast process is surounded by intervined collagen fibrils, that outline the future dentinal tubule;

The fibrils run circumferentially and perpendicular to the process;

Each tubule is occupied by a process or its ramifications;

Peritubular dentin (deliminated dental tubule) is poor in collagen and more mineralized than the rest of dentin.

The dentin between tubules is referred to as intertubular dentin.

Dentin tubules and odontoblasts

CROSS SECTION OF DENTINDENTINAL TUBULES(С); INTERTUBULAR DENTIN (В); PERITUBULAR DENTIN(А).

INTER- AND PERITUBULAR DENTIN

DENTINAL TUBULES

Dentin tubules Collagen matrix of dentin

Dentin tubules with odontoblastprocesses and their branches

PROPERTIES OF DENTINThe inorganic component - dentin is composed of 87% inorganic hydroxyapatite crystals, fluorapatite and carbonatapatite in the form of small plates;

Organic component - 13% collagen fibers with small amounts of other proteins and water;

Collagen is mainly typ I with small amounts of type III and V;

There are fractional inclusions of lipids and noncollagenous proteins;

The noncollagenous matrix proteins pack the space between collagen fibrils and accumulate along the periphery of dentinal tubules;

Thay comprise the following:

Dentin phosphoprotein – phosphophoryn, dentin sialoprotein, dentin matrix protein 1, osteonectin, osteocalcin, bone sialoprotein, osteopontin, proteoglycans and ect.

PHYSIOLOGY OF DENTIN

Metabolism in dentin is ensured by the pulp;

Metabolism is performed by odontoblast processes;

ODONTOBLASTS

They form a layer lining the periphery of the pulp and have a process extending in the dentin;

The number of dental tubules with odontoblasts are of 59 000 to 76 000 per square millimeeter in a coronal dentin;

NERVE ENDINGS AROUND ODONTOBLASTS IN THEPREDENTIN

FUNCTIONS OF THE ODONTOBLASTSDuring dentinogenesis:

1 Synthesising function:Odontoblastat synthesized proteins, matrixmacromolecules and collagen;

2 Secreting function:Odontoblasts secreted Β-fibers (collagen) and amorphous organic and inorganic matter;

3. Both structurise and mineralise dentinal matrix.

During functional stage odontoblasts:

1. Continued formative function;

2. Ensure the exchange of the dentin;

3. Providing a link betweenenamel, dentin and dentalpulp;

5. They provide sensitivity of the

dentin;

5. They have protective function;

Reparative dentin;Sclerotic dentin;Secondary and tertiarydentinogenesis.

PHYSIOLOGIC SECONDARYDENTINOGENESIS

It represents the slower-paced deposition of dentin matrix that continues after completion of the crown and root of the tooth and spans a lifetime;

While secondary dentin is deposited all around the periphery of the tooth, its distribution is asymmetric, with greater amounts on the floor and roof of the pulp chamber.

TERCIARY DENTINOGENESISIt describes the focal secretion of dentin in response to external influences (dental caries, tooth wear, trauma, and other tissue injury;

Tertiary dentin encompasses a broad spectrum of responses:Regular tertiary dentin;

Displastic atubular dentin;

Reactionary dentin;

Reparative dentin.

Atubular dentin: areas without tubules

Atubular dentin: areas without tubules

Types of secondary dentin

Regular

Line of demarcation:

stain dark

Clinically:

The increase of the dentin thickness and the closure

of the pulp

horns make it much less possible to expose the pulp

chamber during preparation.

Irregular

Line of demarcation:

stain dark

Clinically:

Functions as a barrier against caries.

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.

Osteodentin: The odontoblasts (cells) are included

in the formed dentin

Circumpulpal

dentin

Response

dentin

REPARATIVE DENTIN AND INCORRECT COURSE OF DENTINAL TUBULES

REACTIONARY DENTIN

Is defined as a tertiary dentin matrix secreted by surviving postmitotic odontoblast cells in responce to an appropriate stimuls;

Such a responce will be made to milder stimuli and represents up-regulation of the secretory activity of the existing odontoblast responsible for primary dentin secretion.

REPARATIVE DENTIN

REPARATIVE DENTINIs defined as a tertiary dentin matrix secreted by a new generation of odontoblast-like cells in response to an appropriate stimuls after the death of the original postmitotic odontoblsts responsible for primary and fisyologic secondary dentin secretion;

Such a response will be made to stronger stimuli and represents a much more complex sequence of biologic processes.

REPARATIVE DENTIN

РЕПАРАТИВЕН ДЕНТИН

SCLEROTIC DENTINSclerotic dentin describes dentinal tubules that have become occluded with calcified material;

When this occurs in several tubules in the same area, the dentin assumes a glossy appearance and becomes translucent;

This is deposition of mineral within the tubule without any dentin formation and diffuse mineralization is occurs with a viable odontoblast process still present;

Because sclerosis reduces the permeability of dentin, it may help to prolong pulp vitality.

DEAD TRACTS

Loss a tubular contents (odontoblast processes) results in dead tracts, wich indicate air in the tubules;

Below the dead tract area is sclerotic dentin, wich protect the pulp from bacteria or bacterial products.

DEAD TRACTS IN THE DENTIN

VITALITY AND SENSITIVITY OF DENTINVitality of dentin is its ability to react following physiological or pathological stimuli.

Forming secondary or tertiary dentin, feeling pain are signs of being vital;

Several theories have been cited to explain the mechanism involved in dentinal sensitivity & vitality: The transducer theory,

the conduction theory,

the modulation theory

the Brännström's hydrodynamic theory.

THE TRANSDUCER THEORY

The transducer theory contend that the odontoblast and its process are capable to mediate neural impulse in the same way as nerve cells;

Contra:

But investigations have proved that no pain is experienced in exposed dentin by application of substance known to bare nerve endings.

The measurement of membrane potential of the odontoblastsshows clearly that this potential is very low to contribute in the pain excitation.

THE CONDUCTION THEORY

The conduction theory (intratubular innervation theory) contend that dentin is richly innervated and those nerves mediate the impulse to the brain.

Some new studies show that predentin and the first layer of circumpulpal dentin (0.2mm) is innervated with nerve fiber from the raschkows plexus.

The fibers run parallel to the tomes fiber in the dentin tubules.

The density of those fiber is much higher in the coronal dentin than cervical dentin. Root dentin doesn’t include such fibers.

Some authors contend that those fibers end at the DEJ, but can not be seen in histological slides.

Contra:

It is uncapable to explain the higher sensitivity at the cemento-enamel junction than that felt at other areas.

The conduction theory

THE HYDRODYNAMIC THEORY

The “hydrodynamic theory”, developed in the 1960’s is the widely accepted physiopathological theory of Dentin Sensitivity.

Temperature, physical osmotic changes or electrical and chemical stimuli and dehydration are the most pain-inducing stimuli.

According to this theory, those stimuli increase centrifugal fluid flow within the dentinal tubules, giving rise to a pressure change throughout the entire dentine.

The movement stimulates intradentinalnerve

receptors sensitive to pressure (BARORECEPTORS),

which leads to the transmission of the stimuli .

This simulation generates pain.

THE HYDRODYNAMIC THEORY

Berman describes this reaction as: “The coefficient of thermal expansion of the tubule fluid is about ten times that of the tubule wall.

Therefore, heat applied to dentin will result in expansion of the fluid and cold will result in contraction of the fluid, both creating an excitation of the 'mechano-receptor'.”

APPEARANCE OF A PAIN IN THEDENTIN

The fluid moves through the tubules

and excites nerves

The incentives on dentine causes

movement of fluid in the tubules

include hot and cold, tactile, evaporative, and osmotic,