Category Archives: Dentin

Age and functional changes in dentin

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Age and functional changes in dentin

(1)    Primary dentin

Primary dentin is formed till root completion.

By age, primary dentin may show gradual reduction in the diameter of the dentinal tubules due to continual deposition of peritubular dentin.

This may lead to decreased permeability and sensitivity of dentin.

(2)    Secondary dentin

Any dentin formed after complete formation of the primary dentin is considered secondary dentin.

After tooth eruption, dentin formation continues at a slower rate throughout life.

This later formed dentin is known as regular or physiologic secondary dentin which may be separated from the primary dentin by a darkly stained line along which the dentinal tubules show sharp bending.

Secondary dentin shows less tubular number per unit area. This change in the structure from primary to secondary dentin is due to the crowding of the odontoblasts which leads finally to elimination of some of them and rearrangement of the remaining odontoblasts.

Secondary dentin may be deposited on the entire pulpal surface of the dentin at uneven rate. It is more pronounced on the floor and roof of the pulpal chamber of posterior teeth. The pulp horns may be obliterated and pulp cavity becomes reduced in size.

in older teeth.

Formation of secondary dentin protects the pulp from exposure

(3) Transparent or Sclerotic dentin

It is regressive alteration in the primary dentin which is characterized by calcification of the dentinal tubules.

-    Mild sufficient stimuli are generated to cause active response on the part of the odontoblasic processes which produce collagen fibers and apatite crystals to begin appearing in the dentinal tubules.

Deposition of apatite crystals is initially only sporadic in the dentinal tubules, but gradually the tubules become filled with a fine meshwork of crystals causing their blocking.

-    Or the odontoblastic processes may undergo fatty degeneration due to mild stimuli and then calcification occurs intratubular.

The refractive indices of dentin in which the tubules are occluded are equalized and such areas become transparent.

Transparent dentin can be demonstrated in ground sections. It appears light in transmitted light and dark in reflected light. Transparent dentin occurs in cases of mild stimuli;

  • As a manifestation of the normal aging process. It is met with, in the teeth of elderly people especially in the roots (particularly near apex), and in the crown midway between the DEJ and the pulp surface.
  • Zones of transparent dentin develop around the dentinal part of type B and C enamel lamellae.
    •    It is found under slowly progressive caries, abrasions, attrition, erosion, cavity preparation.

Such areas of sclerotic dentin are denser and more harder than normal dentin and show decreased permeability.

Sclerotic dentin is regarded as a defensive reaction to dentin and may help prolong pulp vitality.

(4) Dead tract

In case of severe dentin injury or stimulation, the dentinal tubules are in occasion emptied either by complete retraction of the odontoplastic processes or by their complete degeneration. Dead tract is noticed in the primary dentin.

Dentin areas characterized by degenerated odontoblastic processes give rise to dead tracts which demonstrate decreased sensitivity.

Dead tracts occur most often in coronal dentin in the area of narrow pulp horns and are frequently surrounded by bands of sclerotic dentin.

Where reparative dentin seals the affected tubules at their pulpal ends, dentinal tubules fill with fluid or gaseous substances.

In the ground sections, empty dentinal tubules entrap air and appear black in transmitted light and white in reflected light.

This dead tract should not be mistaken from normal dentin when ground sections are made and the odontoblastic processes disintegrate.

(5) Reparative dentin (Tertiary dentin)

It is a localized formation of dentin on the pulp dentin border formed in reaction to severe stimuli such as caries, operative procedures and erosion.

In such cases the odontoblastic processes become exposed or cut and the cells are severely damaged and may degenerate.

The reparative dentin is characterized by great reduction of the tubules that run in twisted course and irregular manner.

Atubuiar dentin

In case of degenerated odontoblasts the undifferentiated cells from the pulp may migrate to the site of injured odontoblasts and differentiate into cells that form dentin.

The structure of the formed dentin is atypical and appears as calcific barrier without the characteristic dentinal tubules and known as a tubular dentin. Osteodentin

During rapid formation of the reparative dentin, some dentin forming cells are often included in the rapidly produced dentin substance. Such cells degenerate and vacate the spaces that they formally occupied and gives similarity to bone tissue and so called osteodentin.

In many cases a combination of types of reparative dentin may be noticed. Frequently reparative dentin is separated from the primary dentin or secondary dentin by a deeply staining demarcation line

(6) Ability to repair

Because the cells of young pulps have high metabolism, so in case of injury recovery occurs rapidly. The potential ability of the pulp-dentin complex to repair itself is reduced by age.

Dentinogenesis

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Dentinogenesis

The odontoblasts that form dentin are differentiated from the ectomesenchymal cells of the dental papilla under the organizing influence of the inner dental epithelium.

Dentinogenesis begins at the incisal edge or cusp tips then spreads down the cuspal slopes, toward the cervical region.

In multi-cusped teeth, dentin formation begins independently at the sites of each future cusp in a genetically determined pattern, spreads down the cusp slopes, and fuses with adjacent formative centers.

Primary dentin formation continues until the external form of the tooth has been completed (till the completion of the root).

Dentin formation does not cease however after the normal anatomy of the tooth has been established but continues, although at a much slower rate. This dentin formed after root formation is known as Secondary dentin.

Dentinogenesis takes place in two phases:

1)    Organic matrix formation :

It is the elaboration of the fibers and the ground substance forming the predentin.

2)    Mineralization :

It involves the calcificatin of the predentin. It begins when a fairly wide band of predentin has been laid down

 

1) Organic matix formation:

After the differentiation of the odontoblasts, the next step in the production of dentin is the formation of the organic matrix.

A- Formation of Mantle Dentin:

Collagen first appears as very distinct large diameter fibrils-The Von Korff fibrils- (0.1 to 0.2 um in diameter) which aggregate in the structureless ground substance immediately below the basal lamina supporting the inner dental epithelium. The fibrils are aligned at right angles to the basement membrane.

In addition to the large diameter fibrils there are small diameter fibrils (of 0.05 urn diameter) formed by the newly differentiated odontoblasts and running randomly between them. These collagen fibrils, together with the ground substance in which they aggregate, constitute the organic matrix of the first formed dentin or mantle dentin.

It has been shown that collagen formation begins at the ribosomal sites related to the cisternae of the rough endoplasmic reticulum. Pro-collagen molecules are then passed, via transport vesicles, to the Golgi complex where they are glycosylated and then, in turn, passed to the secretory pole of the cell in distinct transport vesicles. Once secreted, the pro-collagen is aggregated into the visibly banded collagen outside the cell.

The ground substance follows a similar synthetic pathway within the odontoblast. The odontoblasts, as they secrete the collagen, are still increasing in size, obliterating the extracellular compartment between them and bringing adjacent odontoblasts into contact. Extensive junctional complexes develop where such contact is made to form a distinct row, or layer, of odotoblasts. The odontoblasts also develop alkaline phosphatase activity along their plasma membranes at this time, an activity probably associated with the transport of calcium into the cell.

As the first collagen of the dentin matrix is being deposited, the plasma membranes of the odontoblasts adjacent to the inner enamel epithelium push out several short stubby processes. On occasion, one of these processes may penetrate the basal lamina and interpose itself between the cells of the inner enamel epithelium to form what will later be an enamel spindle. As the odontoblast forms these processes, it also buds off a series of small, membrane-bound vesicles known as matrix vesicles, which come to lie between the large diameter collagen fibrils.

As the matrix is formed, the odontoblast begins to move towards the center of the pulp. As it does, one of the short stubby processes becomes accentuated and is left behind to form the principal extension of the cell, the odontoblastic process. It is into this site that apatite crystallites are introduced.

They first appear within matrix vesicles as single crystals which grow rapidly and rupture from the confines of the vesicle to spread as a cluster of crystallites until they fuse with adjacent clusters to form small islands that subsequently fuse and form a continuous calcified layer. As the apatite crystallites are deposited, they obscure the collagen fibrils of the matrix. In this way mantle dentin is formed.

B-Formation of Circumpulpal Dentin:

After mantle dentin has formed, the remaining primary dentin is deposited. This dentin forms the bulk of the tooth and its formation is essentially similar to that of mantle dentin with three notable exceptions.

First, the collagen fibrils forming the matrix are much smaller in diameter (0.05 um), are more closely packed and interwoven with each other, and are generally aligned at right angles to the tubules.

Second, the ground substance is now an exclusive product of the odontoblast. The organic matrix of the mantle dentin incorporates some preexisting ground substance of the dental papilla. But, because of the close packing of the odontoblast layer, all the ground substance for circumpulpal dentin must originate from these odontoblasts and not from the ground substance of the dental papilla.

Third, the pattern of mineralization is slightly different. No matrix vesicles are present as circumpulpal dentin forms. Instead, mineralization spreads from the preexisting mineralized mantle dentin. Organic matrix must always formed before mineral salts can be deposited within it, hence there is always a band of unmineralized dentin, predentin, between the odontoblasts and mineralized dentin.

C-Formation of the Peritubular Dentin.

The rate of coronal dentin deposition is about 4 to 8 um per day and occurs in a regular or incremental manner. As new dentin is formed, further changes occur within the previously formed dentin. The odontoblastic process diminishes in diameter and is responsible for the deposition of a collar of more highly mineralized dentin around itself in the space so created. This collar of hypermineralized dentin is the peritubular dentin.

2) Mineralization of dentin

The initial mineralization of dentin via matrix vesicles has already been described. Continued mineralization of the dentin intertubular matrix results from the deposition of apatite crystallites around and within the collagen fibrils. The crystals are arranged with their long axis paralleling the fibril axes. It has been shown that dentin mineralization follows three different patterns, namely a linear pattern, a globular pattern, and a combination of the two.

A- Linear Calcification

Linear calcification indicates the deposition of crystals along an uninterrupted front and is the principal pattern of mineralization found in the mantle dentin.

B- Globular Calcification.

Globular, or calcospheric calcification refers to the deposition of crystals in several areas of the matrix at one time. With continued mineralization, globular masses develop which enlarge and eventually fuse to form a single calcified mass. This type of mineralization is seen principally in the circumpulpal dentin formed just below mantle dentin.

C- Combination pattern.

In the rest of the circumpulpal dentin a combined pattern of calcification occurs with a globular phase alternating with a linear phase.


Innervation of Dentin

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Innervation of Dentin

Nerves enter the pulp space in company with the afferent blood vessels and generally follow a similar course once within the pulp chamber. They ultimately form an extensive nerve plexus adjacent to the cell- rich- zone. This plexus of nerves is called the subodontoblastic plexus or plexus of Raschkow and found in the roof and lateral wall of the coronal pulp and usually does not appear in the root canal.

This plexus is characteristic of both deciduous and permanent teeth. It is not apparent in the young pulp until root formation nears completion.

As the nerve bundles enter the pulp, they consist of a mixture of both myelinated and unmyelinated large – and small-diameter fibres.

Most of the nerve bundles terminate in the subodontoblastic plexus as free nerve endings; however, small number of axons loses their Schwann cell coating and pass between the odontoblast cell bodies to enter the dentinal tubules in close approximation to the odontoblastic process.

The intratubular nerve fibrils have not been found in the dentinal tubules farther than 200 um from the pulp. They are located in the pulp, predentin, and mineralized dentin close to pulp.

Such intratubular nerves are found only in about one of ten tubules or less in human coronal dentin and are fewer in root dentin. They characteristically contain neurofilaments, neurotubules, numerous mitochondria and many small vesiclar structures,

  • Other nerves loop into the predentin or lie on the predentin surface as a loop and pass out again to the region of the plexus.
  • A few of the nerve endings among the odontoblasts may not be sensory, but may be autonomic (adrenergic) in nature. These endings would play a role in stimulating the odontoblasts such as deposition of reparative dentin in respond to cavity preparation.

Sensitivity of Dentin

One of the features of the pulp- dentin complex is its sensory function. The only sensation appreciated by this complex is that of pain, no matter the stimulus applied.

This pain is often diffuse, making it difficult on occasion to locate the pain.

Many stimuli evoke a painful response which applied to dentin. Dentin is not uniformly sensitive. It is most sensitive at the dentino-enamel junction, quite sensitive close to the pulp.

An explanation of pain transmission through dentin has long been thought. Several theories have been advanced to explain this process.

  1. The transduction theory.
  2. The direct innervation theory.
  3. The hydrodynamic theory.

1-    The transduction theory

The transduction theory maintains that the odontoblast serves as a receptor which conduct an impulse from the dentino-enamel junction, via the odontoblasic process to its cell body where it contacts nerve endings.

Several factors both support and refuse this theory.

The support lies in the fact that:

  1. The odontoblast is of neural crest origin, it could have retained an ability to transduce and propagate an impulse.
  2. Also a close relationship of the odontoblasts with nerve endings is supportive of this theory. A space resembling a synaptic cleft is found between the nerve and the cell.
  3. A third supportive factor is that adjacent odontoblasts have gap junctions that are sites of electrotonic coupling.

 

The arguments against this theory are:

  1. There are no vesicles containing neurotransmitter substances in the odontoblasts or their processes adjacent to the nerve endings. These vesicles would be needed for the existence of synapses at these sites.
  2. It is believed that the odontoblast process do not extend much farther than about third of the way through dentin which makes it difficult to account for impulse reception.
  3. Measurements of odontoblastic membrane potentials have been found to be low to permit transduction, as are potentials of other known nonconductive tissues.

 

2-    The Direct innervation theory

This theory maintains that stimuli directly interact with nerve endings in the dentinal tubules. This theory is the oldest and was supported when it was believed that nerves extended to the DEJ.

Today, it is difficult to believe that stimuli can traverse the dentin into the predentin zone where nerve receptors are located.

  • Another argument against this theory, is that developmental studies have shown that the plexus of Raschkow and the intratubular nerves do not establish themselves until some time after the tooth has erupted, yet newly erupted teeth are sensitive.
  • In addition, the application of local anesthetics or silver nitrate (a protein precipitant) to exposed dentin does not eliminate dentin sensitivity.

 

3- The Hydrodynamic theory

It is based on the presence of fluid in the dentinal tubules. This dentinal fluid responds mechanically to stimuli applied externally to dentin. It proposes that the fluid movement through the tubule distorts the local pulpal environment and is sensed by the free nerve endings in the plexus of Raschkow.

Thus when dentin is first exposed, small blebs of fluid can be seen on the cavity floor, which when dried, a greater loss of fluid is induced leading to more movement and therefore pain.

The increased sensitivity at the DEJ is explained by the profuse branching of the tubules in this region (terminal branches).

The hydrodynamic hypothesis also explains why anesthetics fail to block dentin sensitivity.

Although many unanswered questions remain, this seems the most reasonable theory of pain conduction through dentin. 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 one time.

Structure of Dentin 2

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Structure of Dentin 1

Structure of Dentin 2

Mantle Dentin

Mantle dentin forms the outer layer of dentin immediately below the DEJ. It is the first layer of dentin formed by the odontoblasts.

It is approximately 20um wide and has an organic matrix consisting of large collagen fibrils (Von Korff fibers) which are arranged at right angle to the dentinal surface paralleling the tubules and fine collagen fibers that run randomly. Mantle dentin is less calcified than the rest of dentin (In the root the large fibers run parallel or oblique to the dentino cemental junction):- No true mantle layer exists in root dentin.

Cireumpulpal Dentin

•All the dentin layers with the exception of the mantle dentin are called cireumpulpal dentin. It consists of fine collagen matrix fibers which wave across each other paralleling the dentinal surface (Perpendicular to the dentinal tubules).

Peritubular Dentin

In both mantle and cireumpulpal dentin, the dentinal tubule is surrounded by hypermineralized ring of dentin forming its wall. It is readily apparent when ground sections of dentin is cut at right angle to the tubules and examined under the light microscope as a transparent zone.

Its width is roughly 0.4 um near the pulpal end of dentin and 0.7um near the DEJ.

The peritubular dentin is sharply demarcated from the intertubular dentin due to its high inorganic and very delicate organic matrix content.

In de-mineralized sections, this is usually lost and the odontoblastic process appears surrounded by empty space which is greater than real diameter of the dentinal tubules.

The formation of the peritubular dentin is a continuous process which can be accelerated by environmental stimuli causing progressive reduction in the size of the tubule lumen and on occasion eventually obliterating it.

Intertubular Dentin

The main body of dentin is composed of intertubular dentin which is located between the peritubular dentin. It consists principally of tightly interwoven network of collagen fibrils in which apatite crystals are deposited within and in between them. The crystals are oriented with their long axis parallel the collagen fibrils. It is less calcified than the peritubular dentin, so in microscopic ground dissections it appears dark surrounding the transparent peritubular dentin.

Incremental lines of Dentin 1- Von Ebner incremental lines

These reflect the rhythmic formation of dentin and variations of structure and mineralization. The distance between the lines corresponds to the daily rate of apposition. In the crown it varies from 4-8um daily and is less in the root.

2-    Contour lines of Owen

These are accentuated incremental lines that reflect disturbances in mineralization. These lines represent hypocalcified bands.

3-    Neonatal line

It is accentuated incremental line that separates the prenatal from postnatal dentin. They could be seen in the all deciduous tooth and only the first permanent molars.

Interglobular Dentin

Considerable proportion of the mineral in dentin is laid down in the form of globules of calcium the calcospherites. Interglobular dentin are interpreted as areas of deficient mineralization between the globules or calcospherites which have failed to fuse completely.

It is prevalent with vitamin D deficiency and increased fluorine intake during dentinogenesis.They are formed chiefly in the coronal circumpulpal dentin close to the DEJ as interglobular hypomineralized areas.

The dentinal tubules pass uninterrupted through them, however, there is no peritubular dentin where the tubules pass through the globules. The interglobular dentin follows the incremental pattern of the tooth. In ground sections they appear black because the organic matter is lost and replaced by air.

Tomes’ granular layer

It appears only in ground sections (L.S or T.S) as a granular thin layer of dentin subjacent to the peripheral zone of hyalinized root dentin. This granular layer can not be seen in decalcified H&E stained section or on E.M. examination.

  • It is found only in root dentin.
  • They do not follow incremental pattern.
  • The dentinal tubules do not cross this granular

    layer.

It may be due to:

  • Interference with mineralization of the entire surface layer of the root dentin prior to the beginning of cementum formation.
  • May be similar to the mode of formation to the larger interglobular spaces seen in the crown.
  • Or result from the looping of the terminal portions of the dentinal tubules in the first formed root dentin.

The Blood Supply of Dentin

An extensive capillary network is present in the subodontoblastic region of the pulp just below the odontoblasts. Some terminal capillary may extend upwards between the odontoblasts to lie against the predentin.

Fenestrations are sometimes found in the capillaries appearing as small pores within their wall. Such pores probably permit the rapid transfer of nutrient materials.

Structure of Dentin 1

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Structure of Dentin 1

The most characteristic histological features of dentin are the closely packed dentinal tubules which traverse its entire thickness and which contain at least part of their length the cytoplasmic extensions of the odontoblasts, the odontoblastic process. Each cell gives rise to one process. The cell bodies of the odontoblasts are aligned along the inner aspect of dentin. They also form the peripheral boundary of the dental pulp.

A thin layer (10-20um thick) of non-calcified dentin (predentin) is present between the calcified dentin and the odontoblatic cell body layer on the pulp surface.

Surrounding and enclosing the dentinal tubules is an extracellular dentin matrix (formed of the hydroxyapatite crystals, organic matter and water).

The collagen fibers of the dentin matrix are arranged in a random network. As, dentin calcifies, the hydroxyapatite crystals mask the individual collagen fibers. Collagen fibers are only visible at the electron microscopic level.

The Dentinal tubules

  • The dentinal tubules are small, canal like spaces that extend through the entire thickness of dentin.
  • The course of the dentinal tubules resemble an “S” shape. Starting at right angle from the pulpal surface, the first convexity of the “S” is directed toward the apex of the tooth. In the root and in the area of the incisal edge and cusps the tubules are almost straight. These are called primary curvatures. Over their entire length, the tubules exhibit minute regular secondary curvatures within the primary one. These secondary curvatures are due to the spiral track of the odontoblasts from the surface towards the pulp.
  •  Since the inner surface of dentin is narrower than the outer surface, the ratio being 1:5, the tubules are more closely packed near the pulp than is the peripheral layers. The ratio between the numbers of tubules per unit area on the pulpal side to that of the peripheral layer of dentin is about 4:1 ratio.

Near the pulpal side their number is about 30,000 to 75,000 tubules per square mm. There are more tubules per unit area in the crown than in the root. The dentinal tubule taper from the pulpal surface outward. Its pulpal diameter is about 3um, while its peripheral end is about lum.

The dentinal tubules present lateral branches termed canaliculi of about 1 um diameter. They branch from the main tubules some what at right angles and at intervals of 1.0-2.0um along its length. These branches may or may not house lateral cytoplasmic extensions of the odontoblastic processes.

The terminal parts of the tubule branch, resulting an increased number of tubule per unit area in mantle dentin (near DEJ).

The presence of dentinal tubules gives dentin the property of permeability which may provide a pathway for the invasion of caries.

The content of the dentinal tubules:

The dentinal tubules are filled with tissue and occupied for part or all of their length by the odontoblastic processes so,

  • The dentinal tubules near the peripheral dentin surface contain amorphous, non cellular-material.
  • The dentinal tubule in intermediate dentin, some tubules clearly contain odontoblastic processes, others apparently empty and contain non-cellular material.
  • All tubules in the inner dentin are occupied by the odontoblastic processes and most of them contain sensory nerve terminal.

In the adult tissue, the extent of the odontoblastic processes varies in the dentinal tubules, however in the early stages of development the processes occupy the whole length of the tubules.

The odontoblastic process (Tomes fibres)

These are the cytoplasmic processes of the odontoblasts that occupy the

dentinal tubules.


Near its base in the predentin, the odontoblastic process shows strands of endoplasmic reticulum, ribosomes, coated vesicles, occasional mitochondria, and abundance of microtubules and filaments arranged in a linear pattern. In calcified dentin, the process shows microtubules, microfilaments and vesicles responsible for the transport and discharge of materials into the periodontoblastic space. The odontoblastic process also show enzymatic activity of oxidative and hydrolytic enzymes. It seems certain that the odontoblastic process is involved in the formation of the peritublar dentin. Terminal branches of the odontoblastic processes may extend to a short distance in the enamel forming enamel spindles.

The Periodontoblastic “Space”

Recent electron microscopic studies show that there is a space between the odontoplastic process and the tubule wall. Tissue fluid within the pulp continued into the dentin through this space. Amorphous substance containing occasional fine mineralized collagen fibers may be seen. Cytoplasmic vacuoles were shown to be discharged from the odontoblastic process to this space.

The odontoblasts

The odontoblasts form a cellular layer lining the periphery of the pulp. Each cell posses a single process extending into a dentinal tubule in the dentin.

In the crown portion of the tooth, the odontoblasts often appear to be arranged in a palisading pattern seemingly forming a layer 3-5 cells thick (Pseudostratified). This is an artifactual appearance caused by crowding of the cells.

The odontoblasts are larger and more in number in the crown than in the root.

In the crown, cell body is columnar in shape, while in the mid portion of the pulp is cuboidal and in the apical part is flattened in appearance.

The odontoblasts vary in its morphological structure depending upon its functional activity.

The odontoblasts in the active synthetic state are columnar in shape of 40um length and 7um diameter showing intensely basophilic cytoplasm with prominent organelles.

These organelles consist of large nucleus located in the basal portion of the cell body (adjacent to the pulp), well- developed Golgi complex located in the dentinal side of the nucleus, numerous mitochondria scattered throughout the cell body, cisternae of rough endoplasmic reticulum, numerous vesicles and membrane- bound granules , microfilaments and micro tubules.

Decreased amount of the intracellular organelles reflects decreased functional activity of the cell. The resting cell shows relatively little cytoplasm and smaller size.

Many complex junctions occur between adjacent odontoblasts which are prominent at the neck of the cell.

DENTIN

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DENTIN

 Dentin is a specialized calcified connective tissue that constitutes the main bulk of the tooth. It is covered by enamel in the crown and by cementum in the root. It surrounds the soft tissue of the pulp.

Dentin and pulp are related tissues embryologically, histologically and functionally forming the dentin- pulp complex.

Dentin forms the hard tissue protective portion of the complex, while the soft tissue pulp portion contains;

  • The cell bodies of the odontoblasts which form dentin.
  • The vascular system which nourishes the avascular dentin.
  • The nerves which provide sensitivity of dentin.

    « The undifferentiated cells which are capable of producing new dentin when necessary.

Dentin is a living and vital tissue since it constitutes the processes of the odontoblasts and neurons.

Physical Properties

  • Dentin is very hard, but its hardness is less than enameJ and more than cementum and bone. The dentin of the permanent teeth is harder than of the deciduous.
  • Dentin is resilient which gives it the capacity to respond to natural masticatory forces.
  • It is light yellow in color.
    • It is permeable to certain molecules which could pass from the pulp to dentin to DEJ, or from the outer environment crossing the enamel to dentin reaching the pulp.

Chemical Properties

Dentin is formed of

  • Inorganic matter 70% by weight
  • Organic matter 20% by weight -Water    10% by weight

The inorganic component consists of hydroxyapatite plate like crystals of O.lum average length (smaller than enamel). Trace elements such as carbonate and fluorine may be also present. The organic matrix consists of

90% collagen (mostly type 1).

8% phosphoprotein and lipids & proteoglycans.

2% ground substance glycoproteins.