enamel

    Cards (69)

    • What is the hardest biological tissue?
      Enamel
    • What is the composition of enamel?
      96% mineral, 2% organic, 2% water
    • What property of enamel allows it to withstand shearing and impact forces?
      High abrasion resistance
    • Why is enamel considered brittle?
      It has low tensile strength and fractures without support from dentin
    • Can enamel repair or undergo replacement?
      No, it cannot repair or undergo replacement
    • What is the vascular and nerve supply status of enamel?
      Enamel is avascular and has no nerve supply
    • What cells are responsible for the formation of enamel?
      Ameloblasts
    • Where is enamel thickest on the tooth?
      Over cusps and incisal edges
    • What is the thickness of enamel over the cusps of permanent teeth?
      1.5 mm
    • What is the thickness of enamel over the cusps of deciduous teeth?
      1.3 mm
    • How does the surface enamel compare to subsurface enamel?
      Surface enamel is harder, denser, and less porous than subsurface enamel
    • What is the mineral component of enamel?
      Hydroxyapatite crystals
    • What lies between the hydroxyapatite crystals in enamel?
      Water
    • What is the organic component of enamel?
      Matrix proteins
    • What are the two types of organic matrix proteins in enamel?
      Amelogenins and non-amelogenins
    • What role do amelogenins and non-amelogenins play in enamel?
      They control the growth and organization of enamel crystals
    • What is the shape of enamel crystallites in cross-section?
      Hexagonal
    • What is the basic structural unit of enamel?
      Enamel rods
    • How are enamel rods arranged?
      Millions of crystallites arranged into rods and interrod enamel
    • What is the diameter and length of each enamel rod?
      1.6 micrometres in diameter and 2.5 mm long
    • How do interrod crystals differ from rod crystals?
      Interrod crystals deviate 40-60 degrees compared to rods
    • How does the orientation and size of enamel rods contribute to enamel properties?
      They contribute to the level of hardness
    • What is the key hole pattern of enamel rods?
      • Clear head and tail regions
      • Arranged in staggered rows
      • Tail of rod lies between two heads in the row below
      • Heads parallel with rod, tails diverge to the long axis of the rod
    • What are the bands of Hunter and Schreger?
      • 10-13 layers of rods follow the same direction
      • Blocks of rods above and below follow different paths
      • Strengthen enamel and prevent cracks from spreading
    • What do incremental lines in enamel demonstrate?
      They demonstrate the growth of enamel
    • What are short period increments in enamel growth called?
      Cross striations
    • What are long period increments in enamel growth called?
      Enamel striae
    • What are cross striations in enamel?
      Lines that cross enamel rods at right angles to long axes
    • What is the common interval for cross striations?
      1.6 micrometres
    • What do striae of Retzius represent?
      Successive positions of the enamel-forming front
    • How do striae of Retzius appear over cusps and incisal edges?
      They don’t reach the surface unless enamel is lost
    • How many cross striations are typically found between adjacent striae?
      7 to 11
    • What happens to striae if there is a metabolic disturbance during amelogenesis or mineralization?
      Attenuated striae occur
    • What are neonatal incremental lines in enamel?
      Marked striae formed at birth reflecting metabolic changes
    • How do rods change during neonatal incremental lines?
      Rods change direction and thickness
    • What happens to rods after neonatal incremental lines?
      Rods eventually turn back again and regain previous orientation
    • What are perikymata incremental lines?
      • Striae that extend to reach the surface of lateral enamel
      • End as fine grooves running circumferentially around the crown
      • Lost through wear unless well protected
      • Mainly seen on labial surfaces
    • What are the stages of amelogenesis?
      1. Pre-secretory
      2. Secretory
      3. Maturation
      4. Post-maturation
    • What occurs during the pre-secretory phase of amelogenesis?
      Cells differentiate into ameloblasts at the future enamel-dentin junction
    • What characterizes the secretory phase of amelogenesis?
      Ameloblasts form matrix enamel without rod formation
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