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DENTIN
DENTIN
Dentin, the most voluminous mineralized connective tissue of the tooth which is hard tissue and also mildly elastic in nature and forms the pulp and provides general form and shape to the tooth, and is also called Substantia eburnea.
It considered as a vital tissue.
The hardness 1/5th of enamel and increase with age
Determine the shape of the crown , the number and size of the root.
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Dentin
Enamel
Cementum
Color of dentin varies from light yellow in deciduous teeth to pale yellow in permanent dentition, becoming darker with age.
It is elastic and subject to slight deformation.
PHYSICAL PROPERTIES
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Harder than bone but softer than enamel.
Lower content of mineral salts in dentin renders it more radiolucent than enamel.
PHYSICAL PROPERTIES
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Consists of 20% organic matter and 10% water & 70% inorganic material.
The organic substance consists of collagenous fibrils and a ground substance of mucopolysaccharides (proteoglycans and glycosaminoglycan).
CHEMICAL PROPERTIES
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The inorganic component consists of hydroxyapatite as in bone, cementum & enamel.
Organic constituents can be removed from the mineral by incineration or organic chelation.
CHEMICAL PROPERTIES
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STRUCTURES OF DENTIN
1. Dentinal tubules
2.Peritublar dentin
3.Intertublar dentin
4.Predentin
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The dentinal tubules follow a gentle ‘S’-shaped curve in the tooth crown and are straighter in the incisal edges, cusps and root areas.
Starting at right angles from the pulpal surface, the first convexity of this doubly curved course is directed toward the apex of the tooth.
DENTINAL TUBULES
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These tubules end perpendicular to the dentinoenamel and dentinocementum junctions.
Dentinal tubule is lined with a layer of peritubular dentin , which is much more mineralized than the surrounding intertubular dentin.
DENTINAL TUBULES
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There are more tubules per unit area in the crown than in the root.
The dentinal tubules have lateral branches throughout dentin, which are termed canaliculi or microtubules.
A few dentinal tubules extend through the dentinoenamel junction into the enamel. These are termed enamel spindles.
DENTINAL TUBULES
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Peritubular dentin has more mineral content and less collagen fibers than the intertubular dentin.
The peritubular dentin forms the walls of the tubules in all the dentin.
The continuous deposition of peritubular dentin causes reduction in the size of tubular lumen.
PERITUBULAR DENTIN
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Forms the main body of dentin.
It is located between the dentinal tubules or, more specifically, between the zones of peritubular dentin.
Intertubular dentin determine the elasticity of the dental matrix and it’s less mineralized than peritubular dentin.
INTERTUBULAR DENTIN
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Is located adjacent to the pulp tissue which is next to cell bodies of odontoblasts.
Is 2 to 6 microns thick, depending on the activity of the odontoblast.
PREDENTIN
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It is the first formed dentin and is not mineralized.
As the collagen fibers undergo mineralization at the predentin - dentin front, the predentin then becomes dentin and a new layer of predentin forms circumpulpally.
PREDENTIN
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1. Primary dentin
a. Mantle
b. Circumpulpal
2.Secondary dentin
3.Reparative dentin
4.Sclerotic dentin
5. Interglobular dentine
TYPES OF DENTIN
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This type of dentin is formed before root completion, gives initial shape of the tooth, it continuous to grow tell 3 years after tooth eruption and forms the major bulk of the dentin.
Mantle dentin
It is the outer or most peripheral part of the primary dentin & is about 20um thick.
PRIMARY DENTIN
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Circumpulpal dentin
forms the remaining primary dentin or bulk of the tooth, represents all of the dentin formed prior to root completion.
PRIMARY DENTIN
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formed after root completion.
Contains fewer tubules than primary dentin.
There is usually a bend in the tubules where
primary and secondary dentin interface.
Secondary dentin forms at a slower rate then
primary dentin.
SECONDARY DENTIN
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REPARATIVE DENTIN
Known as reactionary, reparative or irregular secondary dentin.
Produces in response to various stimuli such attrition, caries, restorative dentinal procedure.
Tertiary dentin deposited rapidly.Produced only at the site of odontoblast activation
by stimuli.
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Collagen fibers and apatite crystals begin appearing in the dentinal tubules.
Apatite crystals are initially only sporadic in a dentinal tubule but gradually fill it with a fine meshwork of crystals.
Found specially in roots.
SCLEROTIC OR TRANSPARENT DENTIN
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Gradually, the tubule lumen is obliterated with mineral, which appears very much like the peritubular dentin.
Sclerotic dentine is generally observed in the teeth of elderly people.
Transparent or light in transmitted and dark in reflected light.
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SCLEROTIC OR TRANSPARENT DENTIN
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Sometimes mineralization of dentin begins in small globular areas that fail to fuse into a homogenous mass. This results in formation of hypocalcified matrix , These are called interglobular dentin.
Forms in crowns of teeth in the circumpulpal dentin just below the mantle dentin.
INTERGLOBULAR DENTIN
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Follows an incremental pattern.
In dry ground section, a small amount of interglobular dentin may be lost and a space appears black in transmitted light .
INTERGLOBULAR DENTIN
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Two types of structural lines can be found in dentine :
The structural lines related to the formation of the dentin are called incremental lines .
The other types of lines are related to the curvature of the dentinal tubules. (Neonatal line)
STRUCTURAL LINES
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The incremental lines (von ebner), or imbrication lines, appear striations or as fine lines at right angles to the dentinal tubules.
The distance between these lines varies between 4 and 8 microns, which is the amount of dentin formed in 24 hours.
INCREMENTAL LINES
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When the tooth comes into functional occlusion, the daily increment decreases.
The course of the lines indicates the growth pattern of the dentin.
INCREMENTAL LINES
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NEONATAL LINE
These lines represent hypocalcified bands.
In the deciduous teeth and in the first permanent molars, the prenatal and postnatal dentin is separated by an accentuated contour line. This is termed the neonatal line.
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This line represent the disturbance in mineralization due to the abrupt change in environment that occurs at birth.
The Neonatal line is present in both enamel and dentine
NEONATAL LINE
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This is a granular layer seen under transmitted light adjacent to cementum. this is known as Tomes’ granular layer.
Slightly increases in amount from the cementoenamel
junction to the root apex.
The odontoblast initially interacts with ameloblasts or root sheath cells through the basal lamina.
GRANULAR LAYER
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With advancing and for functional requirements number of changes are seen in dentin , the following important are:
Formation of secondary dentin.
Sclerotic dentin.
Formation of reparative dentin.
Dead tract.
AGE AND FUNCTIONAL CHANGES
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The odontoblast processes disintegrate, & the empty tubules are filled with air.
Appear black in transmitted light & white in reflected light.
Often observed in the area of narrow pulpal horns because of crowding of odontoblasts.
DEAD TRACTS
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Demonstrate decreased sensitivity.
Appear to a greater extent in older teeth.
Probably the initial step in the formation of sclerotic dentin.
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DEAD TRACTS
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Infected dentine is the outer layer and is softened and contaminated with bacteria. It is irreversibly denatured and not remineralized
Affected dentine has a demineralized phase, but not yet invaded by bacteria. It can be remineralized.
AFFECTED & INFECTED DENTIN
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In clinical restorative treatment of dentine during cavity preparation it is infected dentine which is completely removed. The affected dentine, which may be remineralized after the completion of restorative treatment, is not removed and is preserved.
AFFECTED & INFECTED DENTIN
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INNERVATIONS OF DENTIN
Plexus of Raschkow (suodontoblastic layer)
The nerve will loose its schwann caoting then pass between the odontoblasts bodies and enter the dentinal tubules ( In crown and fewer in the root )
High at D E J
High near the pulpal surface
Less sensitive area