Dentin Overview and Types

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Questions and Answers

What serves as the primary protective function of dentin?

Makes up the majority of the tooth

Protects pulp (correct)

Facilitates taste sensation

Supports enamel

Which type of dentin forms after the primary dentin during the life of a tooth?

Coronal dentin

Sclerotic dentin

Secondary dentin (correct)

Mantle dentin

What is mantle dentin primarily composed of?

Type III collagen (correct)

Type I collagen

Type IV collagen

Type II collagen

What is the role of odontoblasts in dentin formation?

They differentiate and secrete organic matrix. Signup and view all the answers

Which type of dentin is characterized by its response to injury or stimulus?

Reparative dentin Signup and view all the answers

What is a key feature of circumpulpal dentin compared to mantle dentin?

No contribution from the subodontoblastic layer Signup and view all the answers

What type of dentin is specifically involved in mineralization and contains hydroxyapatite crystals?

Reactionary dentin Signup and view all the answers

What is the structure of the collagen fibrils in circumpulpal dentin?

Type I and closely packed Signup and view all the answers

What structure remains between the odontoblast and the mineralizing front?

Predentin Signup and view all the answers

What are the large diameter collagen fibrils found in mantle dentin referred to as?

von Korff’s fibres Signup and view all the answers

What initiates the differentiation of odontoblasts?

Epithelial cells of HERS Signup and view all the answers

Which type of dentin is characterized by its slower formation rate?

Radicular dentin Signup and view all the answers

What is the primary chemical composition of dentin?

70% Inorganic, 20% Organic, 10% Water Signup and view all the answers

What is the structural difference between radicular dentin and coronal dentin?

Radicular dentin has different structural and compositional properties Signup and view all the answers

Which aspect differentiates mantle dentin from circumpulpal dentin?

Mantle dentin fibrils are larger Signup and view all the answers

What occurs at the mineralization front in mineralization?

Formation of hydroxyapatite crystals Signup and view all the answers

How does the permeability of dentin change with age?

Decreases with age Signup and view all the answers

What type of dentin is formed in response to stimuli such as caries?

Tertiary dentin Signup and view all the answers

Which of the following best describes the color of dentin?

Light yellowish to dark with age Signup and view all the answers

What is the primary feature of the primary curvature of dentinal tubules?

S-shaped curve Signup and view all the answers

What is the main function of intratubular dentin?

Forms a hypermineralised ring within the dentinal tubule Signup and view all the answers

How many tubules are found per square mm near the pulpal surface?

50,000 – 90,000 Signup and view all the answers

What do contour lines of Owen indicate?

Zones of hypocalcification in dentin Signup and view all the answers

What distinguishes predentin from dentin?

Predentin is unmineralised and forms before dentin Signup and view all the answers

Which theory of dentin sensitivity is the most widely accepted?

Fluid/hydrodynamic theory Signup and view all the answers

What happens to dentin formation after a tooth reaches functional occlusion?

Daily increment of dentin decreases Signup and view all the answers

Which type of dentin is affected by abrasion or caries leading to the formation of reparative dentin?

Intertubular dentin Signup and view all the answers

What does the neonatal line represent in dental anatomy?

A reflection of environmental changes at birth Signup and view all the answers

What is the primary characteristic of sclerotic dentin?

It forms in response to external stimuli Signup and view all the answers

What structure does the term 'Tomes granular layer' refer to?

A granular zone adjacent to cementum Signup and view all the answers

Which statement about interglobular dentin is true?

It contains areas of hypomineralised dentin Signup and view all the answers

Which of these statements is true about dentinal tubules?

They taper in diameter from pulp to DEJ Signup and view all the answers

What is the primary role of odontoblasts?

To produce dentin Signup and view all the answers

What characterizes the branching of dentinal tubules?

Represents terminal branching of tubules Signup and view all the answers

Study Notes

Dentin Overview

Dentin is the hard tissue portion that forms the bulk of a tooth.
It protects the pulp and supports the enamel.

Types of Dentin

Coronal dentin: Found in the crown of the tooth.
Radicular dentin: Found in the root of the tooth.
Primary dentin: The initial dentin formed during tooth development.
Secondary dentin: Formed after root formation is complete. A narrow band bordering the pulp. Fewer tubules than primary dentin.
Tertiary dentin: Also called reparative or irregular secondary dentin. Located on the pulp dentin border. Produced by cells directly affected. Created in reaction to various stimuli, like caries, abrasion, etc.
- Can be produced if odontoblasts are killed due to exposure and/or damage.
- Odontoblasts are replaced by migration of undifferentiated cells (cell rich zone/undifferentiated perivascular cells).
Mantle dentin: First formed mineralised dentin. Outermost part of primary dentin. Seen between the DEJ and interglobular dentin. About 20 µm thick. Fibrils run perpendicular to the DEJ and are larger in size than those in circumpulpal dentin. Few defects.
Circumpulpal dentin: Forms bulk of the tooth dentin that forms before root completes. Collagen fibrils are smaller and closely packed. More mineralized than mantle dentin (4%).
Sclerotic dentin: Also called transparent dentin; has similar refractive indices. Seen in older individuals, especially in the roots. Stimuli include caries, abrasion, cavity preparation, and erosion. Collagen fibers and apatite crystals appear in the tubules.
Interglobular dentin: Areas of hypo/unmineralised dentin. Found in the crown of teeth in circumpulpal dentin just below mantle dentin. Mineralization is largely globular.
Intratubular dentin: Also called peritubular dentin. A hypermineralized ring of dentin found within the dentinal tubule. Found to be 9% or 40% more than intertubular dentin
Predentin: Unmineralized dentin found adjacent to the pulp tissue. 2-6 µm wide.

Dentin Formation (Dentinogenesis)

Primary dentin: Can be of two types, mantle dentin and circumpulpal. Mantle dentin forms from ectomesenchymal cells. It secretes organic matrix collagen (type III) into preexisting ground substance of dental papilla. Collagen fibrils are of large diameter (0.1-0.2µm). These structures intermingle with aperiodic fibrils (type VII collagen), dangling from the basal lamina, arranged at right angles to the basal lamina. Organic matrix of dentin contains these large-diameter collagen fibrils. Also, the odontoblast gives out short stubby processes that penetrate the basal lamina (enamel spindles). Odontoblasts bud off matrix vesicles (membrane-bound vesicles) that contain calcium and phosphate ions, alkaline phosphatase enzyme, and calcium binding lipids. This permits hydroxyapatite crystals to form within the matrix vesicles. Crystals grow, form islands of calcifications that fuse. Collagen fibrils obscured. Mineral deposition lags behind organic formation. A layer of unmineralised matrix (predentin) forms between the odontoblast and the mineralization front.
Circumpulpal dentin Formation: Intercellular space between the odontoblast is obliterated, and the organic matrix has no contribution from the subodontoblastic layer. Collagen fibrils are smaller, type I & tightly packed; interwoven and aligned at right angles to the odontoblastic process. No matrix vesicles. Mineralization involves heterogeneous nucleation.

Dentin Tubules

Course: S-shaped curve (primary curvature). Doubly curved course starting at right angles to the pulpal surface and ending perpendicular to the DEJ and CDJ.
- First convexity is directed towards the tooth's apex. Odontoblasts crowd moving from DEJ to pulp.
- Smaller oscillations (secondary curvatures) within the primary curvatures.
Extent: Crown – DEJ to pulp. Root – CDJ to pulp.
Diameter: 2.5 µm near pulp, 1.2 µm in mid-portion, and 900 nm near the DEJ.
Density: Tubules are farther apart in periphery and closer near pulp. Near pulpal surface: 50,000-90,000 tubules/mm². More tubules in crown than root.
Branching: Major branching (500-1000 µm diameter). Represent terminal branching of tubules. More frequent in root dentin than in coronal dentin.

Dentin Composition

Inorganic content: 70% hydroxyapatite crystals (plate-shaped, smaller than enamel). Phosphates, carbonates, sulfates, fluoride.
Organic content: 20%. Collagen types I, III, V (not arranged in bundles), lipids, and non-collagenous proteins.
Water: 10%

Dentin Sensitivity

3 theories for pain transmission:
- Direct neural stimulation
- Fluid/hydrodynamic theory
- Transduction theory

Dentin's Contents in Tubules

Odontoblastic process.
Dentinal fluid (dental lymph?).
Lamina limitans.
Peritubular dentin
Nerve endings (predentin and inner dentin—up to 100-150 μm from pulp).

Dentin's Clinical Considerations

1mm² of exposed dentin = 30,000 damaged cells.
Use non-irritating insulating substances to seal exposed dentin.
Spread of caries:
- Tubular system undermines enamel at the DEJ.
- Microorganisms invade.
- Dentin sensitivity is not a symptom of caries unless pulp is affected.
Trauma from operative instruments.
Aspiration of odontoblast within the tubule.
Reparative dentin forms below odontoblastic layer.

Important Structures and Junctions

Dentinoenamel Junction (DEJ)* and Cementodentinal Junction (CDJ)

Age Changes in Dentin

Vitality of dentin, reparative dentin, dead tracts, sclerotic dentin.

Dentin's Incremental Growth Lines

Dentinogenesis is rhythmic with alternating phases (activity and quiescence).
Daily rhythmic deposition of matrix, with hesitations.
Incremental lines (von Ebner) represent daily formative processes.
Best seen in longitudinal sections, running perpendicular to dentinal tubules.
Distance between lines varies (4-8 µm in crown, much less in root).
Daily increments decrease after the tooth reaches functional occlusion.
Contour lines of Owen: Accentuated incremental lines, matrix and mineralization process disturbances; represent hypocalcified areas. Earlier referred to a line resulting from the coincidence of secondary curvatures of neighboring dentinal tubules.
Neonatal line: Accentuated contour line, seen in deciduous and permanent first molars. Reflects abrupt environmental changes at birth. Separates prenatal and postnatal dentin. Dentin matrix formed before birth is better quality. Can be a zone of hypocalcification.

Tomes Granular Layer

In dry ground sections, a granular zone is adjacent to cementum in transmitted light.
Amount increases from the CEJ to root apex.
Caused by coalescing and looping of terminal portions of dentinal tubules.
Earlier seen as minute hypomineralised areas of interglobular dentin, which are only spaces visible in ground sections. Not in H&E stained sections or electron micrographs. Looping is related to a slower rate of dentin formation in the root.

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Description

Explore the essential aspects of dentin, the hard tissue that forms the bulk of a tooth. This quiz covers various types of dentin, including coronal, radicular, and primary dentin, along with their roles in tooth protection and development.