Untitled Quiz

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.
• 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.