Dental Anatomy: Dentin Overview

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Questions and Answers

What is the primary function of dentin in the tooth structure?

  • Enclose the root
  • Store minerals
  • Support enamel (correct)
  • Produce enamel

What type of dentin occupies the peripheral area where the basement membrane was previously present?

  • Mantle dentin (correct)
  • Tertiary dentin
  • Primary dentin
  • Circumpulpal dentin

What is the primary type of collagen found in the organic matrix of mantle dentin?

  • Type II collagen
  • Type VII collagen
  • Type I collagen
  • Type III collagen (correct)

What is the term used for the layer of unmineralized matrix between the odontoblast and the mineralizing front?

<p>Predentin (C)</p> Signup and view all the answers

What type of dentin is formed as a response to stimuli and is characterized by its reactive nature?

<p>Tertiary dentin (C)</p> Signup and view all the answers

What type of odontoblast process may penetrate the basal lamina to form enamel spindles?

<p>Short stubby processes (A)</p> Signup and view all the answers

In circumpulpal dentin formation, what is the nature of the collagen fibrils?

<p>Type I and closely packed (B)</p> Signup and view all the answers

What type of dentin is known for its calcification islands that form during its development?

<p>Mantle dentin (B)</p> Signup and view all the answers

Which of the following is not a type of dentin mentioned?

<p>Cervical dentin (A)</p> Signup and view all the answers

What cellular origin do odontoblasts differentiate from?

<p>Ectomesenchymal cells (D)</p> Signup and view all the answers

What type of mineralization is characterized by a slow rate of dentin formation?

<p>Linear mineralization (B)</p> Signup and view all the answers

Which component forms the bulk of the tooth before root formation is complete?

<p>Circumpulpal dentin (C)</p> Signup and view all the answers

What is the primary characteristic of radicular dentin compared to coronal dentin?

<p>It is structurally and compositionally different. (A)</p> Signup and view all the answers

Which type of dentin is formed after root formation is complete?

<p>Secondary dentin (A)</p> Signup and view all the answers

What contributes to the hardness of dentin compared to enamel?

<p>Organic matrix and tubular architecture (D)</p> Signup and view all the answers

What initiates the differentiation of odontoblasts during root dentin formation?

<p>Epithelial cells of HERS (A)</p> Signup and view all the answers

Which type of dentin is associated with localized formation in response to stimuli?

<p>Tertiary dentin (B)</p> Signup and view all the answers

Which mineral is primarily responsible for the inorganic content of dentin?

<p>Calcium phosphate (C)</p> Signup and view all the answers

What is the primary curvature of dentinal tubules characterized by?

<p>S-shaped curves (A)</p> Signup and view all the answers

What explains the increase in the permeability of dentin with age?

<p>Decreased patency of tubules (A)</p> Signup and view all the answers

What is the diameter of dentinal tubules near the pulp?

<p>2.5 μm (D)</p> Signup and view all the answers

Which type of dentin is primarily located between the dentinal tubules?

<p>Intertubular dentin (B)</p> Signup and view all the answers

What is the significance of the neonatal line in dentin?

<p>It separates prenatal and postnatal dentin. (A)</p> Signup and view all the answers

What causes the Tomes granular layer to increase in amount?

<p>Coalescing and looping of terminal portions of dentinal tubules (B)</p> Signup and view all the answers

Which structure represents a hypermineralised ring of dentin found within the dentinal tubule?

<p>Intratubular dentin (B)</p> Signup and view all the answers

What does the fluid/hydrodynamic theory explain about dentin sensitivity?

<p>Fluid movement in tubules affects nerve endings. (C)</p> Signup and view all the answers

How do density and distribution of tubules change from the pulp to the periphery?

<p>Closer near the pulp and farther apart in the periphery. (A)</p> Signup and view all the answers

What is the primary reason for the formation of reparative dentin?

<p>Response to stimulus such as caries or abrasion (B)</p> Signup and view all the answers

What occurs to the odontoblastic process in cases of caries?

<p>It disintegrates and leaves a filled tubule. (C)</p> Signup and view all the answers

Which lines represent disturbances in the mineralisation matrix?

<p>Contour lines of Owen (B)</p> Signup and view all the answers

What is typically seen in areas of interglobular dentin?

<p>Hypomineralisation (A)</p> Signup and view all the answers

What is the role of the odontoblastic process?

<p>To extend cytoplasmic processes into dentinal tubules (B)</p> Signup and view all the answers

Which type of dentin is recognized as having similar refractive indices and is often referred to as transparent dentin?

<p>Sclerotic dentin (D)</p> Signup and view all the answers

Flashcards

Dentin

Hard tissue forming the bulk of a tooth, protecting the pulp and supporting enamel.

Primary Dentin

The initial dentin formed during tooth development.

Mantle Dentin

Outermost layer of primary dentin, formed first.

Circumpulpal Dentin

The larger inner portion of primary dentin.

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Tertiary Dentin

Dentin formed in response to tooth damage or irritation.

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Odontoblasts

Cells responsible for forming dentin.

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Predentin

Unmineralized layer of dentin between odontoblasts and mineralizing front.

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Matrix Vesicles

Membrane-bound vesicles containing substances important in dentin mineralization.

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Dentinogenesis

The process of dentin formation.

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Collagen Fibrils

Protein fibers forming the organic matrix of dentin.

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Mineralization in dentin

The process where calcium phosphate crystals form in dentin, making it hard.

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Dentin types

Dentin is categorized into primary (mantle, circumpulpal), secondary, and tertiary dentin based on formation timing and stimuli.

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Secondary dentin

Dentin formed after root formation, often a narrow band around the pulp, fewer tubules than primary.

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Dentinal tubules

Tiny channels in dentin, they run from the pulp to the dentin surface; varying shapes, crucial for sensitivity.

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Dentin Composition

Dentin is primarily hydroxyapatite crystals (inorganic, 70%), collagen (organic, 20%), and water (10%).

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Dentin Properties

Dentin is harder than bone & cementum, softer than enamel, more radiolucent, and has greater compressive strength than enamel.

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Tomes Granular Layer

A layer of fine branches of radicular odontoblasts that form a granular surface.

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Secondary Curvatures

Smaller oscillations within the primary curvatures of dentin.

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Dentin Tubule Extent

Dentin tubules extend from the crown's DEJ to pulp and from the root's CDJ to pulp.

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Dentin Tubule Diameter

Dentin tubule diameter varies, with 2.5 μm near the pulp decreasing to 1.2 μm in the middle, and 900 nm near the DEJ.

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Dentin Tubule Density

Tubules are closer near the pulp and farther apart in the periphery, with 50,000-90,000 tubules/mm2 near the pulp.

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Dentin Tubule Branching

Dentin tubules branch extensively; major branches are wider and more common in root dentin.

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Intratubular Dentin

Hypermineralized ring within a dentinal tubule.

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Intertubular Dentin

The main body of dentin between tubules.

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Interglobular Dentin

Hypomineralized areas in the crown's circumpulpal dentin, below mantle dentin.

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Incremental Growth Lines

Lines reflecting rhythmic dentin formation phases of activity and quiescence.

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Contour Lines of Owen

Accentuated incremental lines representing disturbances in mineralisation.

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Neonatal Line

Accentuated contour line separating prenatal and postnatal dentin in deciduous and early permanent teeth.

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Odontoblastic Process

Cytoplasmic extensions of odontoblasts, extending into dentinal tubules.

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Study Notes

Dentin Overview

  • Dentin is the hard tissue forming the bulk of a tooth.
  • It protects the tooth's pulp.
  • It supports the tooth's enamel.

Dentin-Pulp Complex

  • Dentin and pulp are embryologically, histologically, and functionally related.

Types of Dentin

  • Coronal dentin
  • Radicular dentin
  • Primary dentin
  • Secondary dentin
  • Tertiary dentin

Primary Dentin

  • Consists of mantle dentin and circumpulpal dentin.

Tertiary Dentin

  • Also known as reparative dentin or reactive dentin.
  • Formed in response to damage or stimulation.
  • Produced by cells that are directly affected.

Sclerotic Dentin

  • Similar refractive indexes
  • Response to stimuli such as caries, attrition, abrasion, cavity preparation or erosion.
  • Appears white in transmitted light and black in reflected light.
  • Collagen fibres and apatite crystals appear in the dentinal tubules.

Intratubular Dentin

  • A hypermineralised ring of dentin.
  • Found within the dentinal tubule. -It is (40%) more mineralised compared to intertubular dentin.

Intertubular Dentin

  • Major body of dentin.
  • Located between dentinal tubules.

Interglobular Dentin

  • Areas of hypomineralised/unmineralised dentin.
  • Found in tooth crowns.
  • Mineralisation pattern is mainly globular.

Dentinogenesis

  • Primary dentin can be of two types.
  • Mantle dentin occupies the peripheral area where the basement membrane was earlier present.
  • Circumpulpal dentin is the remaining larger segment of dentin.

Odontoblast Differentiation

  • Important for understanding the formation of normal and reparative dentin.

Mantle Dentin Formation

  • Odontoblasts differentiate from ectomesenchymal cells.
  • Secrete collagen (type III) into existing ground substance of dental papilla.
  • Collagen fibrils are large (0.1-0.2µm) and called von Korff's fibres.
  • These fibres intermingle with aperiodic fibrils (type VII collagen).
  • They sit at right angles to the basal lamina.

Matrix Vesicles and Crystal Formation

  • Odontoblasts release matrix vesicles containing calcium, phosphate, alkaline phosphatase, and calcium-binding lipids, enabling hydroxyapatite crystal formation within the vesicles.

Dentin Tubule Course, Extent, and Diameter

  • Dentinal tubule course is generally S-shaped curve, called primary curvature.
  • They make a double curve, starting perpendicular to the pulpal surface and ending perpendicular to the DEJ and CDJ
  • Extent: crown - DEJ to pulp and root - CDJ to pulp
  • Tubules are longer than the thickness of dentin.
  • Diameter: 2.5μm near the pulp, and 1.2μm in the mid portion, and 900μm near the DEJ.

Dentin Tubule Density and Branching

  • Tubules are farther apart in the periphery and closer near the pulp.
  • Tubules per unit area in the pulpal surface are 50,000-90,000.
  • Major and more frequent branching is in the root compared to the crown.

Secondary Dentin

  • Formed after root formation is complete.
  • A narrow band bordering the pulp.
  • Fewer tubules than primary dentin.
  • Different from primary dentin and has a boundary between it and primary dentin.

Reparative Dentin

  • Reaction to various stimuli including abrasion, erosion, and caries.
  • Odontoblasts are killed and replaced by migrated undifferentiated cells.
  • This forms the reparative dentin.

Dead Tracts

  • Odontoblastic processes are lost and the empty tubules are filled with air
  • Can be caused through various procedures.

Contour Lines of Owen

  • Disturbed matrix and mineralisation process results in hypocalcified areas.
  • Accentuated incremental lines that are a result of coincidence of neighbouring dentinal tubules

Neonatal Line

  • Found in deciduous and permanent first molars.
  • Shows an abrupt change in environment, occurring at birth.

Tomes Granular Layer

  • In dry ground sections, a granular zone adjacent to cementum in transmitted light.
  • Increase in amount occurs from the CEJ to the root apex.
  • Produced by coalescing and looping of terminal portions of dentinal tubules.

Predentin

  • Located adjacent to pulp tissue. -~2-6µm wide
  • Unmineralised dentin.

Chemical Composition

  • 70% inorganic content is hydroxyapatite crystals that are smaller than enamel.
  • Other inorganic components are phosphates, carbonates, sulfates, and fluoride.
  • 20% organic content consists of collagen types I, III, V. and other non-collagenous proteins and lipids.
  • Water makes up approximately 10%.

Non-Collagenous Proteins

  • Amelogenins
  • Dentin Phosphoprotein (DPP)/ Phosphoryn.
  • Dentin Sialoprotein (DSP).
  • Dentin Glycoprotein (DGP).

Dentin Sensitivity

  • There are 3 theories related to pain transmission through dentin.
  • Direct Neural Stimulation
  • Fluid/Hydrodynamic Theory
  • Transduction Theory

Contents of Dentinal Tubules

  • Odontoblastic process
  • Dentinal fluid (dental lymph)
  • Lamina limitans
  • Peritubular dentin
  • Nerve endings (predentin and inner dentin)

Clinical Considerations

  • 1mm² of exposed dentin contains 30,000 cells that could be damaged.
  • It's important to seal exposed dentin with non-irritating insulators against bacteria, drugs, undue operative trauma, thermal changes, and irritating restorative materials.

Spread of Caries

  • The tubular system undermines the enamel at the DEJ.
  • It enables invasion of microorganisms.
  • Dentin sensitivity is not a symptom of caries unless the pulp is affected.

Trauma from Operative Instruments

  • Trauma may result in odontoblast aspiration.
  • Reparative dentin formation occurs in the subodontoblastic layer.

Age Changes

  • Dentin vitality, reparative dentin, dead tracts, and sclerotic dentin undergo modifications.

Age and Dentin Vitality

  • Odontoblasts are an integral part of dentin.
  • Dentin reacts to physiologic and pathologic stimuli.
  • Dentin is laid down throughout life.

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