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z OE > chemistry of hydroxyapatite > Flashcards

chemistry of hydroxyapatite Flashcards

1
Q

what will disturbance in initial enamel matrix deposition lead to?

A

hypoplasia

  • defects occuring during secretory stage
  • manifest as pits and grooves on enamel surface
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2
Q

what will defects during enamel maturation lead to?

A

hypomineralisation / hypomaturation

  • intact surface but opaque appearance and soft
    • discoloured
  • hypomature
    • not fully converted into the final tissue
  • hypomineralised
    • insufficient mineral deposition
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3
Q

what does hypocalcified mean?

A
  • Tissue is fully mature but
  • Mineral deposition hasn’t gone to completion
  • Full thickness of crown has been deposited
  • Normal shape
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4
Q

what is amelogenesis imperfecta

A

Inherited defect of dental enamel, affecting quality and/or quantity of enamel being laid down

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5
Q

give examples of inherited enamel defects

what is the result of them?

A
  • DEJ defects results in an enamel layer that shears easily
  • Secretory stage defects result in insufficient crystal elongation and leave the enamel layer very thin and disorganized
    • Layer can be highly mineralised
  • Maturation stage defects, i.e. deficient matrix degradation, produce thick but soft enamel
    • Rapidly degrades
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6
Q

what is amelogenesis imperfecta caused by?

A

mutations in the human genome

at several different loci

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7
Q

what mutations can lead to hypoplastic amelogenesis imperfecta?

A
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8
Q

what mutations can lead to hypomaturation amelogenesis imperfecta?

A

mutation at 4q13.3

dominant

  • affecting amelotin
  • Overexpression & loss of amelotin leads to amelogenesis imperfecta
    • involved in transition and maturation stage
    • involved in reformation of the basement membrane
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9
Q

what does this show?

A
  • brown-mottled hypomature enamel
  • male with X-linked AI
  • enamel is undermineralised
    • contains non-degraded protein
      • Mutation in cleavage site Leads to retention of excessive amount of protein in the tissue when it undergoes maturation
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10
Q

what does this show?

A
  • alternating areas of normal and hypomature enamel
  • affected female member of family with X-linked AI
    • only half of the tissue is compromised
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11
Q

what are common causes of environmental defects of enamel?

A
  • infectious disease in childhood
    • temporary interruption of normal enamel development
  • fluorosis
    • prolonged ingestion of fluoride excess 5ppm
    • fluoride incorporated in mineral at great excess
    • premature hypermineralisation
    • opacity is irregular
  • ingested supplements are incorporated into matrix
    • pigmentation
    • irreversible
  • dietary deficiencies
    • affect outer layer of tissue
  • trauma
    • during development
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12
Q

describe the changes in physiology during the maturation stage of enamel

A

Ruffle ended

  • Engaged in secretion of enzymes that degrade the matrix
  • Active ion transport
  • Transport ions required for mineralisation process
  • Lower pH

Resorption of protein fragments and water

  • pH is raised back to physiological levels

oscillating pH between low and neutral allows you to accumulate more stable mineral and dissolve more soluble mineral

More perfect formation of hydroxyapatite

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13
Q

why does the pH drop and rise during maturation stage?

A
  • acidification is necessary for degradation
  • EMSP1 works best at lower pH
  • allows dissolution of less stable pH
  • ameloblasts express carbonic anhydrase II during maturation stage
  • CAII produces HCO3-
    • neutralises acid
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14
Q

how is pH regulated during the secretory stage of amelogenesis?

A

Ameloblasts express basal membrane NBCe1 - ion transport protein

  • Allows them to transport bicarbonate ions from the enamel organ into the ameloblast
  • HCO3 - is then secreted apically via AE2 in exchange for Cl- ions
  • therefore pH is stable
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15
Q

how is pH kept by smooth ended ameloblasts during the maturation stage of amelogenesis?

A

pH oscillates in maturation stage

  • Smooth-ended ameloblasts may secrete HCO3 - to raise pH
  • Transport across the cells of bicarbonate is insufficient to neutralise pH
  • Due to lots of mineralisation taking place
  • Carbonic anhydrase 2 - produces bicarbonate ions
  • Both aid regulation of pH back to physiological levels
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16
Q

how is pH kept by ruffled ended ameloblasts during the maturation stage of amelogenesis?

A

pH is not stable but oscillates in maturation stage

  • Ruffle-ended ameloblasts produce an extracellular pH of 5-6
  • No NBCe1
    • No longer pumps ions across membrane
  • AE2 in lateral membrane instead of apical
    • Role in pumping biocarbonate ions out of the cell instead of enamel space
  • ATPase in apical membrane
    • Actively transports protons across the membrane
    • Acidificates the environment
    • Active transport
17
Q

what is the pattern of mineralisation?

A

Starts at cusp

Progresses down tooth crown

18
Q

how does surface enamel differ from the underlying core enamel?

A

Harder

less porous

less soluble

19
Q

how does apatite growth on the crystal surfaces occur?

A

two ways :

  1. rapid growth in epitaxial direction (above each hexagon) forms elongated hexagonal crystals
  2. thickening on the side prism planes at slow rate
20
Q

what substitutions can take place in hydroxyapatite?

what effects do they have?

A

F- for OH- :

  • stabilizing effect
  • caries prevention
  • fluoride taken up passively from circulation
    • only incorporated if in saturation

CO3 2- for OH- or PO4 3- :

  • destabilizing effect
  • much higher solubility product of enamel
  • developmental substitution

Mg2+ for Ca2+:

  • destabilizing effect
  • Cation substitutions
  • occurs in small quantities
21
Q

why does a fluoride substitution have a stabilising effect?

A

Fluoride ion fits more closely within calcium triangle

  • High charge density and symmetry of fluoride ion reduces lattice energy
  • more stable salt
  • a flatter plane
22
Q

what is the most stable salt?

A

Most stable is mixture of fluorapatite and hydroxyapatite

  • 50:50 mixture
  • 100x more stable
  • dispersion of hydroxy ions along the c acid allows hydrogen bonding between fluoride
23
Q

how does the mineral composition of enamel change while aging?

A

Older enamel -

  • hydroxyl increases
    • Relates to remineralisation
  • Decrease in carbonate content
  • Decrease acid phosphate content
    • Incorporated during initial formation
    • Adopting a more perfect hydroxyapatite as maturation occurs

The youngest secretory enamel is the most soluble and the solubility decreases with advancing developmental stages

  • More stable as development advances

z OE (35 decks)

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