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What is the primary structural unit of enamel?
What is the primary structural unit of enamel?
Which tissue surrounds the loose connective tissue known as pulp?
Which tissue surrounds the loose connective tissue known as pulp?
Which mineral is the principal component of enamel?
Which mineral is the principal component of enamel?
How thick is enamel at the cusps of permanent teeth?
How thick is enamel at the cusps of permanent teeth?
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What is the main characteristic of enamel regarding its regenerative capacity?
What is the main characteristic of enamel regarding its regenerative capacity?
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What is the composition percentage of organic matrix in enamel?
What is the composition percentage of organic matrix in enamel?
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What is the approximate length of an enamel rod?
What is the approximate length of an enamel rod?
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Which junction forms where cementum and dentine meet?
Which junction forms where cementum and dentine meet?
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Enamel is primarily derived from which embryonic layer?
Enamel is primarily derived from which embryonic layer?
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What are bon Ebner lines characteristic of in dentine?
What are bon Ebner lines characteristic of in dentine?
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Which layer of the pulp is directly adjacent to the dentine?
Which layer of the pulp is directly adjacent to the dentine?
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What is a primary characteristic of sclerotic dentine?
What is a primary characteristic of sclerotic dentine?
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The process of odontogenesis results in the transformation of dental papilla into what?
The process of odontogenesis results in the transformation of dental papilla into what?
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What is the typical distance of long period lines in dentine?
What is the typical distance of long period lines in dentine?
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Which region of the pulp contains numerous undifferentiated cells?
Which region of the pulp contains numerous undifferentiated cells?
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What often triggers tertiary dentine deposition?
What often triggers tertiary dentine deposition?
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What is the primary function of the odontoblast layer?
What is the primary function of the odontoblast layer?
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What best describes the permeability of dentine?
What best describes the permeability of dentine?
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The network of nerves in the pulp is referred to as:
The network of nerves in the pulp is referred to as:
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What do the cross striations in enamel indicate?
What do the cross striations in enamel indicate?
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Which characteristic distinguishes enamel striae (Striae of Retzius) from other enamel features?
Which characteristic distinguishes enamel striae (Striae of Retzius) from other enamel features?
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What is the significance of the neonatal line in dental biology?
What is the significance of the neonatal line in dental biology?
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Which feature is described as resembling tufts of grass and arises at the dentino-enamel junction?
Which feature is described as resembling tufts of grass and arises at the dentino-enamel junction?
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What is the primary function of the scalloping pattern at the dentino-enamel junction?
What is the primary function of the scalloping pattern at the dentino-enamel junction?
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Which of the following statements is true about enamel lamellae?
Which of the following statements is true about enamel lamellae?
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Which statement accurately describes enamel spindles?
Which statement accurately describes enamel spindles?
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What rhythm do enamel striae of Retzius follow to reflect the enamel formation process?
What rhythm do enamel striae of Retzius follow to reflect the enamel formation process?
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What is a distinguishing characteristic of perikymata on tooth enamel surfaces?
What is a distinguishing characteristic of perikymata on tooth enamel surfaces?
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Which describes the location and appearance of enamel tufts?
Which describes the location and appearance of enamel tufts?
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What is the primary characteristic of pre-renal failure?
What is the primary characteristic of pre-renal failure?
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Which stage of chronic renal failure involves the highest percentage of nephron loss?
Which stage of chronic renal failure involves the highest percentage of nephron loss?
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What condition can lead to intra-renal failure?
What condition can lead to intra-renal failure?
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How is post-renal failure typically addressed for recovery?
How is post-renal failure typically addressed for recovery?
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Which of the following statements is true about renal insufficiency?
Which of the following statements is true about renal insufficiency?
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What is the result of a 'back-pressure' caused by post-renal failure?
What is the result of a 'back-pressure' caused by post-renal failure?
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What is the primary role of dentine in a tooth?
What is the primary role of dentine in a tooth?
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Which factor is NOT known to affect amelogenesis?
Which factor is NOT known to affect amelogenesis?
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What percentage of the population is reported to have at least one permanently affected tooth due to enamel defects?
What percentage of the population is reported to have at least one permanently affected tooth due to enamel defects?
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Which component represents the majority of the organic matrix in dentine?
Which component represents the majority of the organic matrix in dentine?
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What happens to enamels' appearance as individuals age?
What happens to enamels' appearance as individuals age?
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What is the primary inorganic component of dentine?
What is the primary inorganic component of dentine?
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In dentinal tubules, what happens to the diameter as it moves from the pulp to the periphery?
In dentinal tubules, what happens to the diameter as it moves from the pulp to the periphery?
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Which condition is characterized by the complete absence of enamel?
Which condition is characterized by the complete absence of enamel?
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What occurs at the periphery of a prism in response to caries?
What occurs at the periphery of a prism in response to caries?
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What is the primary cellular component located within dentinal tubules?
What is the primary cellular component located within dentinal tubules?
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Study Notes
Teeth Structure
- Teeth are composed of three mineralized tissues: Enamel, Dentine, and Cementum.
- A loose connective tissue - the pulp - is surrounded by these hard tissues.
- Enamel and Dentine meet at the Dentino-enamel junction (DEJ).
- Cementum and Dentine meet at the Cemento-Dentinal junction (CDJ).
Amelogenesis
- Enamel is derived from ectoderm.
- Secreted by ameloblasts.
- Produced once in a lifetime and has no regenerative capacity.
Enamel Physical Properties
- Thickest over cusps and incisal edges.
- 2.5mm thick cusps in permanent teeth, 1.3mm in deciduous teeth.
- Exhibit high abrasion resistance but is extremely brittle.
Enamel Chemical Properties
- Primarily composed of Calcium Hydroxyapatite (HAP):
- Makes up 95-96% by weight.
- Present as crystallites.
- Contains a small percentage of water (2% by weight) and organic matrix (1-2% by weight), including enamel proteins.
Enamel Histology
- Highly mineralized, making it difficult to study.
- Ground sections are needed for light microscopy, as enamel is lost in demineralized sections.
Enamel Rod (Prism)
- The basic structural unit of enamel.
- Composed of millions of HAP crystals packed.
- 2.5mm long and 5-6 micrometres thin.
- Runs from the DEJ to the surface.
- Its diameter corresponds to the diameter of the cell that produced it.
- Cross sections reveal various patterns:
- Pattern 1 (near DEJ and surface).
- Pattern 2.
- Enamel striae.
Cross Striations
- Lines running perpendicular to the long axes of enamel prisms in longitudinal sections.
- Found at intervals of 4-6 micrometres across the rods.
- Reflects a circadian rhythm in enamel matrix secretion.
Enamel Striae (Striae of Retzius)
- Obliquely running lines across prisms in longitudinal sections, appearing as concentric rings in cross sections.
- Represent successive positions of the enamel forming front.
- Occur due to a circaseptan (7-day) rhythm of enamel formation and demarcation between activity and quiescence.
- Exaggerated striae may indicate systemic influences.
Perikymata
- Incremental growth lines appearing as linear grooves on the tooth enamel surface.
- Run circumferentially around the crown.
- Perikymata grooves.
- Perikymata ridges.
Neonatal Line
- A type of striae of Retzius present in both enamel and dentine of primary teeth, rarely in permanent dentition.
- Marks the time of birth, usually appearing darker and larger than other striae.
- Used in forensic dentistry to determine the child's death time (before or after birth).
Dentino-Enamel Junction (DEJ)
- Boundary between enamel and dentine, exhibiting a scalloping pattern prominent under cusps and incisal edges.
- Concavities toward enamel and generally less mineralized.
- Provides stress relief during mastication.
- Features extending from dentine to enamel can be observed:
Enamel Tufts
- Resemble tufts of grass extending from the DEJ into the inner third of enamel.
- Occur at approximately 100-micrometre intervals.
- Travel in the same direction as prisms.
- Considered hypo-mineralized areas.
Enamel Spindles
- Short, linear, dark, club-shaped structures extending up to 25 micrometres into enamel.
- Forged by entrapment of odontoblast processes between ameloblasts.
- Commonly found beneath cusps, best visualized in longitudinal sections.
Enamel Lamellae
- Linear enamel defects running through the entire thickness of enamel.
- Narrower, longer, and less common than enamel tufts.
- Most visible in transverse sections.
- May arise developmentally due to:
- Incomplete maturation of a prism group.
- Cracks after eruption caused by occlusal loading.
Enamel Clinical Considerations
- Age Changes:
- Wear away slowly with age, known as attrition.
- Tend to darken with age.
- Caries:
- Vulnerable to acid attacks (demineralization).
- Mineral loss occurs at the periphery of the prism.
- Restoration:
- Acid etching is used for restoration.
- Secondary caries can occur.
- Developmental Enamel Defects:
- Common, affecting 8-80% of the population.
- Amelogenesis (enamel formation) is sensitive to environmental changes.
- Causes of Enamel Defects:
- Infection: Turner tooth, Hutchinson's teeth.
- Radiation: Enamel defects or complete absence of teeth.
- Trauma: Hypoplasia.
- Fluoride: Fluorosis.
- Hereditary: Amelogenesis imperfecta.
Dentine
- Forms the bulk of the tooth.
- Ectomesenchymal in origin.
- Produced by odontoblasts (dentinogenesis).
- Covered by enamel in the crown and cementum in the root.
- Provides protection for dental pulp and support for overlying enamel.
- A vital tissue containing odontoblast processes and nerves.
- Tubular structure.
Dentine Physical Properties
- Pale yellow in color.
- Harder than bone and cementum but softer than enamel.
- Organic matrix and tubular structure provide compressive, tensile, and flexural strength.
- Permeable.
Dentine Chemical Properties
- 70% inorganic, 20% organic, and 10% water by weight.
- Inorganic component: Calcium Hydroxyapatite.
- Organic matrix: Collagen (90%) - Type 1, and traces of III and V.
Dentine Structural Components
- Odontoblastic processes.
- Dentinal tubules.
- Peritubular dentine.
- Intertubular dentine.
Odontoblastic Processes
- Extensions of odontoblast cell bodies into dentinal tubules.
Dentinal Tubules
- Functional unit of dentine.
- Extend radially from pulp to DEJ and CDJ.
- Contains odontoblastic process, occasional nerve fibers and extracellular fluid.
- Taper from pulpal (2.5 micrometres) to periphery (1 micrometre).
- Tubular Density:
- Near pulp: 50,000/mm^2.
- In the middle: 40,000/mm^2.
- May appear as alternating light and dark bands, known as "Bon Ebner lines," running perpendicular to tubules.
- 4 micrometres apart in the crown, 2 micrometres in the root.
- Long Period Lines:
- Andresen lines.
- 10-20 micrometres apart.
Dentine Clinical Considerations
- Highly sensitive tissue, leading to dentine sensitivity upon exposure.
- Permeable, causing pulpal irritation.
- Tertiary dentine deposition occurs in response to severe injury.
- Sclerotic dentine is deposited in response to external stimuli, like slowly advancing caries.
Dental Pulp
- Derived from ectomesenchyme (dental papilla).
- During dentinogenesis, dental papilla becomes dental pulp.
Dental Pulp
- Contained within the pulp chamber of the crown and the root canal.
- Connects with the periodontium at the apical foramen.
- Remains active throughout life, responding to external stimuli.
Pulp Regions
- Odontoblast layer:
- Peripheral layer adjacent to dentine.
- Subodontoblast layer:
- Cell-free zone (of Weil):
- Directly beneath odontoblasts.
- Contains processes of fibroblasts, traversing blood vessels, and a network of nerves (plexus of Raschkow).
- Cell-rich zone:
- Numerous undifferentiated cells: fibroblasts, macrophages, lymphocytes.
- Cell-free zone (of Weil):
- Pulp core:
- Periphery: Smaller vessels and nerves.
- Associated with a sudden reduction in renal function accompanied by accumulation of waste products in the blood.
- Marked decrease in urine output, or rarely, urine flow ceases.
Renal Failure
- Pre-renal failure:- Impairment of renal blood flow, usually reversible upon identifying and correcting the cause.
- Intra-renal failure:- Damage occurs to the nephron itself, which may be reversible, depending on the severity.
- Post renal failure:- Obstruction in the urinary collecting system distal to the kidney.
Chronic Renal Failure
- Gradual loss of kidney function over months to years, ultimately irreversible, leading to end-stage renal disease.
- Three stages:
- Decreased renal reserve:- Loss of up to 50% of nephrons.
- Renal Insufficiency:- Loss of 75-80% of nephrons.
- End-stage renal disease:- Loss of >90% of nephrons.
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