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Questions and Answers
What type of collagen fibers primarily make up the circumpulpal dentin?
What type of collagen fibers primarily make up the circumpulpal dentin?
Which process initiates the formation of hydroxyapatite crystals during dentin mineralization?
Which process initiates the formation of hydroxyapatite crystals during dentin mineralization?
Which feature distinguishes globular calcification from linear calcification?
Which feature distinguishes globular calcification from linear calcification?
What is the diameter of type III collagen fibers, such as Von Korff's fiber?
What is the diameter of type III collagen fibers, such as Von Korff's fiber?
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What is the arrangement of collagen fibers in the root of the tooth?
What is the arrangement of collagen fibers in the root of the tooth?
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Which type of dentin forms the main bulk of a tooth?
Which type of dentin forms the main bulk of a tooth?
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What primarily initiates the process of globular calcification?
What primarily initiates the process of globular calcification?
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What is the orientation of collagen fibers in mantle dentin?
What is the orientation of collagen fibers in mantle dentin?
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What characterizes interglobular dentin?
What characterizes interglobular dentin?
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Which statement best describes the Tomes granular layer?
Which statement best describes the Tomes granular layer?
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What is a principal feature of the dentino-enamel junction (DEJ)?
What is a principal feature of the dentino-enamel junction (DEJ)?
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What is the most sensitive part of the dentin?
What is the most sensitive part of the dentin?
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What role do odontoblasts play in dentin mineralization?
What role do odontoblasts play in dentin mineralization?
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Which theory of pain transmission through dentin suggests that nerve endings are directly stimulated?
Which theory of pain transmission through dentin suggests that nerve endings are directly stimulated?
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What is a defining feature of the dentino-cemental junction (DCJ)?
What is a defining feature of the dentino-cemental junction (DCJ)?
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How does interglobular dentin differ from other types of dentin regarding mineralization?
How does interglobular dentin differ from other types of dentin regarding mineralization?
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What is the first layer of dentin formed during dentinogenesis?
What is the first layer of dentin formed during dentinogenesis?
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Which statement accurately describes the process of mineralization in dentin formation?
Which statement accurately describes the process of mineralization in dentin formation?
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What type of dentin is produced continuously throughout life by odontoblasts in their resting state?
What type of dentin is produced continuously throughout life by odontoblasts in their resting state?
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What is the significance of Tome's fiber in dentin structure?
What is the significance of Tome's fiber in dentin structure?
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What changes occur to odontoblasts as they enter a quiescent state?
What changes occur to odontoblasts as they enter a quiescent state?
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This type of dentin develops during the lifetime of a tooth but following trauma or decay:
This type of dentin develops during the lifetime of a tooth but following trauma or decay:
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What morphological change happens to odontoblasts during their differentiation phase?
What morphological change happens to odontoblasts during their differentiation phase?
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What structure increases the surface area for the secretion of dentin matrix in odontoblasts?
What structure increases the surface area for the secretion of dentin matrix in odontoblasts?
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Study Notes
Dentin
- Dentin is the yellowish tissue that makes up most of the teeth.
- It is harder than bone, but softer than enamel.
- It is primarily composed of apatite crystals of calcium and phosphate.
- Dentin is sensitive to pain, pressure, and temperature.
Physical Properties
- Young dentin is light yellow, darkening with age.
- Dentin is elastic and resilient.
- It is harder than bone but softer than enamel.
Chemical Properties
- Dentin is 70% inorganic material by weight.
- 20% is organic content.
- 10% is water.
Histologic Structure of Dentin
- Odontoblasts line the pulpal surface of dentin.
- Each odontoblast has a long, thin process called a dentinal tubule.
- These tubules run through the entire thickness of the dentin.
- The tubules follow a gentle S-shaped curvature in the crown of the tooth, starting at the pulpal surface.
- The curvature is less prominent in the root.
Dentinal Tubules
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Tubules are perpendicular to the dentinoenamel and dentino-cemental junctions.
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Near the root tips, the tubules are nearly straight, and more spread out in the enamel surface of dentin.
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The diameter at the pulpal end is larger (3-4 micrometers) than at the enamel end (1 micrometer).
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Primary curvature is a straight course in incisal/occlusal thirds and dentin of the root.
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Secondary curvature is an S-shape following the primary curvature.
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The diameter near the pulp is 4 micrometers, and at the outer surface is 1 micrometer.
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The number of tubules per unit area at the pulpal surface is about 4 times that of the enamel surface.
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There are more tubules per unit area in the crown compared to the root.
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Lateral branches of dentinal tubules are called canaliculi or microtubules (1 micrometer in diameter).
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Some tubules extend through the DEJ into enamel called enamel spindles.
Contents of Dentinal Tubules
- Dentinal tubules contain an odontoblastic process.
- Tissue changes in dentin occur within the extracellular fluid.
- Afferent nerve endings are present in the tubules.
- Odontoblastic processes contain organelles in the predentin area (mitochondria, RER, lysosomes, microtubules, intermediate filaments).
- Organelles are fewer in the odontoblastic processes of mineralized dentin.
Odontoblastic Process
- Odontoblastic processes have fine branches that extend along their course, contained within lateral extensions of dentinal tubules.
- These branches unite with those of adjacent processes to form a plexus beneath the DEJ.
- Some odontoblast process branches cross the DEJ and extend into enamel as enamel spindles.
- In the root, dentinal tubules end in Tome's granular layer.
Peritubular Dentin (Intratubular Dentin)
- High mineralization (40% minerals, 90% mineralization at the pulpal tissue fluid inside the tubules, or dental lymph).
- In transverse sections, odontoblastic processes appear surrounded by empty space.
- It appears as shining rings surrounding black dots (odontoblastic process spaces) in transverse ground sections.
Intertubular Dentin
- Makes up the majority of primary dentin between dentinal tubules.
- Less mineralized than peritubular dentin, with approximately half the volume made up of organic matrix.
- Collagen fibers are aligned around the tubules.
- Hydroxyapatite crystals are approximately 0.1 micrometers in length and aligned parallel with the collagen fibers.
- Appears darker than peritubular dentin in demineralized sections, and contains more organic matrix.
Types of Dentin
- Primary physiologic dentin
- Secondary physiologic dentin
- Tertiary dentin (reparative dentin, reactionary dentin)
- Circumpulpal dentin
- Peritubular dentin
- Intertubular dentin
Predentin
- A layer of unmineralized dentin, 2-6 micrometers wide, located adjacent to pulp tissue.
- It is the first formed dentin matrix.
- Its thickness depends on the odontoblasts' activity.
Primary Dentin
- Formed before the root is complete.
- Divided into mantle dentin and circumpulpal dentin.
- Mantle dentin is the first formed dentin in the crown and is 20 µm thick. Its organic matrix is formed by collagen fibrils arranged perpendicular to the DEJ, these are von Korff's fibers.
- Circumpulpal dentin forms the bulk of the tooth. Its collagen fibrils are smaller in diameter (0.05 µm). and more closely packed.
Circumpulpal Dentin
- The remaining portion of primary dentin.
- Forms the bulk of the tooth.
- Collagen fibrils are smaller in diameter.
- Slightly more mineralized than mantle dentin.
- Calcification is a hybrid of linear and mixed mechanisms.
Secondary Dentin
- Formed after root formation is completed and progresses throughout life.
- Formed at a slower rate than primary dentin.
- Dentinal tubules are less regular.
- Separated from primary dentin by a demarcation line.
Tertiary Dentin
- Also known as reparative or reactionary dentin.
- Secreted in response to injury or irritation of the overlying dentin or enamel.
- It can be localized, with dentin being laid down only in the affected area.
- If dentin is produced by pre-existing odontoblasts, it is reactionary; if produced by newly differentiated odontoblast-like cells, it is reparative.
Hypocalcified Structures of Dentin: Incremental Lines of Von Ebner
- Incremental lines of Von Ebner are alternative bands that show the rhythmic deposition of dentin matrix, approximately every 5 days.
- The distance between them is about 20 µm.
Hypocalcified Structures of Dentin (Neonatal Line)
- An accentuated line of von Ebner that separates prenatal from postnatal dentin, and is seen in all deciduous teeth and the first permanent molars.
- It's produced by the disturbance in nutrition.
Interglobular Dentin
- Unmineralized or hypomineralized areas of dentin where the pattern of dentin mineralization is globular in nature.
- Found in circumpulpal dentin, just below the mantle dentin in the crown.
- Odontoblastic processes pass uninterrupted through the tissue.
Tomes Granular Layer
- Found adjacent to cementum.
- Thickness increases from the CEJ to the root apex.
- Contains small black dots visible in ground sections, which are not hypo-mineralized areas.
- Dentinal tubules do not cross this layer.
- Doesn't follow an incremental pattern of formation.
- They may represent smaller areas of interglobular dentin than seen in the crown.
- May result from looping of the terminal ends of D. tubules due to different orientations of odontoblast processes during initial dentin formation.
Dentino-Cemental Junction (DCJ)
- Smooth boundary, but difficult to determine exactly.
- Marked by Tomes' granular layer.
Dentino-Enamel Junction (DEJ)
- Scalloped, with convexities toward the dentin.
- Tight junction due to interdigitation of dentin and enamel crystals.
- Interdigitation of collagen fibers of dentin with enamel's HA crystals.
Dentin Sensitivity
- Dentin is very sensitive to various stimuli (cold, air, cavity preparation, heat, electric stimuli).
- Most sensitive area is the DEJ.
- Sub-odontoblastic layer contains a nerve plexus called Raschkow's plexus.
Theories of Pain Transmission Through Dentin
- Direct neural stimulation theory
- Odontoblastic transduction theory
- Hydrodynamic theory
Dentinogenesis
- Process of dentin formation.
- Occurs in two steps:
- Matrix formation: (predentin).
- Mineralization: crystals.
Life Cycle of Odontoblasts
- Odontoblasts arise from undifferentiated mesenchymal cells in dental papilla.
- U.M.C divide giving two cells, one of them remaining undifferentiated.
- The other cell differentiates into odontoblasts.
- Differentiated odontoblasts are short cells with multiple short processes arising from the distal end of the cell.
- Odontoblasts, after differentiation, becomes columnar cells, and densely packed together.
- They're connected by junctional complexes.
- Odontoblasts contain abundant cytoplasm, mitochondria, rough endoplasmic reticulum, and Golgi apparatus.
- They also contain secretory granules, and ribonucleic acid, and alkaline phosphatase enzymes.
- Odontoblasts enter a resting stage after complete root formation and continue to produce secondary dentin throughout life.
Age Changes of Dentin
- Secondary dentin is produced at a slower rate than primary dentin.
- Its dentinal tubules are less regular.
- Its formation starts after root formation, and continues throughout life.
- Separated from primary dentin by a demarcation line.
- Filled with calcified materials to decrease permeability of the dentin, protecting the pulp.
Sclerotic Dentin (Transparent Dentin)
- Develops due to mild stimulus or aging.
- Calcified material occludes the tubules, leading to a transparent appearance.
- Common in the apical third of the root and midway between the crown and pulp.
- A protective response to prolong tooth vitality.
Dead Tracts (Opaque Dentin)
- Caused by severe stimulus (e.g. erosion, deep carries, severe attrition).
- Odontoblastic processes die or retract, leaving empty dentinal tubules.
- Appears dark in transmitted light and white in reflected light.
- Bound by sclerotic dentin.
- Sometimes empty tubules are obliterated by minerals called a blind tract.
Dentinogenesis
- Two steps
- Formation of the matrix (predentin).
- Mineralization (crystals).
Types of Dentin Mineralization
- Globular calcification: appears in the mineralization front beneath DEJ after a band of 10-20 µm of predentin is formed.
- Linear calcification: occurs when the rate of Dentinogenesis decreases, and the crystals spread more regularly.
- Mixed calcification: linear and globular calcification that may appear in circumpulpal dentin.
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