Dentin Notes

Primary, Secondary, And Tertiary Dentin Types Of Dentin

 Primary dentin

• Dentin which is formed before root completion is known as primary dentin
• There are two types of primary dentin
  1. Mantle dentin
     • It is first formed dentin in the crown
     • It is the outermost part of the primary dentin
     • It contains larger von Korff s fibres
     • It provides a cushioning effect to the tooth
  2. Circumpulpal dentin
     • It is the primary dentin that outlines the pulp chamber

 Secondary dentin

• Secondary dentin is a narrow band of dentin bordering the pulp
• Secondary dentin is the dentin that is formed after root formation
• Secondary dentin contains fewer tubules
• This reduces the overall permeability of dentin
• Secondary dentin represents continued, slower deposition of dentin by odontoblasts

3. Tertiary dentin

• Tertiary dentin is dentin produced by odontoblasts in response to pulpal irritation caused by chemical, thermal, or microbial stimuli
• Tertiary dentin contains very few irregular tubules
• Tertiary dentin is subclassified into
• Reactionary dentin
• Tertiary dentin is deposited by pre-existing odontoblasts
• Reparative dentin
• Tertiary dentin is deposited by newly differentiated odontoblast-like cell

Read And Learn More: BDS Previous Examination Question And Answers

Osteodentin

• Osteodentin  is cellular inclusions within the matrix of reparative dentin.
• Osteodentin  is seen in vitamin A deficiency and in conditions where ameloblasts fail to differentiate properly.
• When a stimulus is a carious lesion, there is extensive destruction of dentin and pulpal damage
• To repair it, tertiary dentin is deposited rapidly with sparse and irregular tubular patterns and some cellular including
• This is referred to as osteopontin

Tome’s granular layer

• A granular appearing area has been seen in the transmitted light-granular layer ;
• Tome’s granular layer  is present just below the surface of the dentin where Features:
• Tome’s granular layer  increases from CEJ to apex of the tooth D Remains unmineralized
• Consists of high concentrations of calcium and phosphorous
• Have a special arrangement of collagen and noncollagenous matrix protein at the interface between dentin and cementum

Cause of development:

• Branching and looping

Denticles

• Calcifications within pulp are called pulp stones or denticles Dystrophic calcification is most commonly seen in pulp. (AIIMS -99)

Denticles Types:

• True pulp stones
• They have dentinal tubules and odontoblastic processes
• False pulp stones
• They do not have dentinal tubules
• Common in coronal pulp
• Free pulp stones
• Entirely surrounded by pulp tissue
• Attached pulp stones
• They are partly fused with dentin
• Embedded pulp stones
• They are entirely surrounded by dentin

 Dentinal Tubules

• Dentinal tubules extend through the entire thickness of the dentin from the dentin enamel junction to the pulp.
• They follow an S-shaped path from the outer surface of the dentin to the perimeter of the pulp.
• The tubules are longer and thicker than dentin because they curve through dentin.
• They end perpendicular to the DEJ and DCJ.

Dentinal tubules Size:

• 2.5 pm in diameter near the pulp.
• 1.2 pm in diameter in the midportion of the dentin.
  900 nm near DEJ.

Dentinal tubules Number:

• There are more tubules per unit area in the crown than in the root.

Dentinal tubules Branches:

• Terminal branches – near the terminals.
• Lateral branches/ canaliculi – throughout the dentin.

Mantle dentin

• Mantle Dentin is first formed dentin in the crown before a tooth erupts into the oral cavity.
• Mantle Dentin is the outermost part of primary dentin.
• Mantle Dentin is 20 pins thick.
• Mantle Dentin provides a cushioning effect to the tooth.
• Mantle Dentin contains larger diameter Von Korff’s fibers.
• Mantle Dentin is less mineralized.
• Mantle Dentin involves globular mineralization.

 Neonatal line

• Neonatal Line is a wide contour line.
• Neonatal Line  separates the dentin formed before birth and that formed after birth.
• Neonatal Line  is found in those teeth mineralizing at birth.
• Neonatal Line  reflects the disturbance in mineralization created by the physiologic trauma of birth.
• The dentin matrix formed prior to birth is usually of better quality than that formed after birth.

Interglobular dentin

• Interglobular Dentin is unmineralized or hypomineralised dentin, and It is prevalent in Vit.
• deficiency and with high exposure to fluoride, It is mostly seen in circumpolar dentin,
• Interglobular Dentin occurs due to a defect of mineralization and not of the matrix, Thus, dentinal tubules run uninterrupted.
• Interglobular Dentin is frequently seen in the cervical and middle third followed by a cuspal and coronal third in the crown,
• Interglobular Dentin is also seen highest in the cervical third followed by the middle third in the root.

Tomes granular layer

• A granular appearing area seen in transmitted light in ground sections of root dentin is called tomes’ granular layer.
• Tomes Granular Layer is present just below the surface of the dentin where the root is covered by cementum.
• This zone increases from the cementoenamel junction to the apex of the tooth.
• They represent sections made through the looped terminal portions of dentinal tubules.
• This layer has a special arrangement of collagen and non-collagenous matrix proteins at the interface between dentin and cementum.
• Interglobular—— dentinft

 

Dead tracts

• Dentinal tubules are emptied by complete retraction of the odontoblast process from the tubule or through the death of the odontoblast.
• The dentinal tubules then become sealed off so that in the ground section air-filled tubules appear by transmitted light as black dead tracts.
• They are most often in coronal dentin.
• Frequently bound by bands of sclerotic dentin.
• These areas demonstrate decreased sensitivity.
• They are the initial step in the formation of sclerotic dentin.

Odontoblasts

• Odontoblasts are columnar cells forming dentin.
• They have oval nuclei present in the basal part of the cell.
• Adjacent to the nucleus, rough-surfaced endoplasmic reticulum and the Golgi apparatus are present.
• Between adjacent cells, there is the presence of tight and desmo.
• soma junctions.
• They are approximately 5-7 pm in diameter and 25-40 pm in length.
• They are present adjacent to the present.
• Their number corresponds to the number of dentinal tubules.
• The odontoblast morphology and its organelles vary with the functional activity of the cell.
• The odontoblast’s cell bodies remain external to dentin, but their processes exist within tubules in the dentin.
• The odontoblasts secrete both collagen and other components of the extracellular matrix.

Tonofilaments

• Tonofilaments are the filamentous strands present in the epithelial cells.
• They are fibrous proteins synthesized by the ribosomes.
• They appear as long filaments with a diameter of approx 8 nm.
• They belong to a class of intercellular filaments.
• They consist of intracellular proteins known as cytokeratins.
• When they become aggregated to form bundles of filaments, they are known as tonofibrils.
• These tonofilaments are not contractile but are important in the maintenance of cell shape and contact between adjacent cells and the extracellular matrix.

 Reparative dentin

• Reparative Dentin is a type of tertiary dentin formed by a newly differentiated odontoblast-like cell.
• Reparative Dentin  is produced by odontoblasts in response to pulpal irritation caused by chemical, thermal, or microbial stimuli.
• Reparative Dentin  is formed only in localized areas in reaction to trauma such as caries or restorative procedures.
• Reparative Dentin  has few and more twisted dentinal tubules.
• The formation of the reparative dentin seals off the zone of injury.
• Due to the irregular nature of the dentinal tubules, it is also known as irregular secondary dentin.

Curvatures in dentin

1. Primary curvatures:

• They are sigmoidal curves.
• They resemble a gentle S-shape curve.
• They are formed as the dentinal tubules follow a gentle curve in the crown which is less curved in the root.

2. Secondary curvatures:

• They are minute, regular and sinusoidal in shape.
• They are present over the entire length of the tubules.

 Osteodentin

• The cells forming tertiary dentin become included in the dentin and are referred as osteopontin.
• Osteodentin is produced in response to rapidly progressing caries.
• Osteodentin  has irregular nature of the dentinal tubules.
• BMP is involved in its production.
• Osteodentin  develops due to a deficiency of vitamin A.

 

 Contour lines of Owen

• These lines result from a coincidence of the secondary curvature between neighboring dentinal tubules
  They are caused by accentuated deficiencies in mineralization
• These are easily recognized in ground sections
• These lines are accentuated because of disturbances in the matrix and mineralization process

 Incremental lines of von Ebner

• Incremental lines of von Ebner appear as fine lines or striations in dentin
• They run at a right angle to dentinal tubules
• They represent a normal rhythmic, linear pattern of dentin deposition in an inward and rootward direction
• Its course indicates the growth pattern of dentin.
• The distance between lines varies from 4-8 mm in the crown too much less in the root
• The daily increment decreases after the tooth reaches functional occlusion