44. Minitutorial. Fluoride Flashcards

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1
Q

History of fluoride use

A
  • 1901-15 Black and McKay saw tooth mottling and low caries incidence in Colorado Springs
  • 1931 Churchill observes high F in Colorado Springs
  • 1948 Dean starts a long term water fluoridation trial in Grand Rapids, MI
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2
Q

How does fluoride prevent caries?

A
  • reduces demineraisation
  • promotes remineralisation
  • inhibits cariogenic bacteria
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3
Q

How does fluoride stop demineralisation?

A
  • mineral phase of tooth enamel and dentine is an impure calcium hydroxyapatite - biological apatite
  • hydroxyapatite forms a crystal lattice
  • fluoride stabilises this by substituting OH ions by ion exchange and by filling gaps left in crystal structure when OH ions displaced during crystal formation
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4
Q

How does OH ion displacement work?

A
  • due to polarity and size, OH ions can’t fit in calcium triangles
  • they’re displaced either above or below (Z coordinates of 0.19 or 0.31 or 0.69 or 0.81)
  • can lead to exclusion from unit cell
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5
Q

How does fluoride affect apatite solubility?

A
  • children in areas of high F have lower tooth decay
  • replacing OH in apatite with F to make fluorapatite reduces solubility of crystals but levels of F in enamel are too low to account for this
  • F incorporates only into outer layers of apatite - across tooth surfaces it’s uneven and fluorapatite concentrates in stagnant areas (pits/fissures)
  • plaque may enhance fluoraapatite formation and dissolution of hydroxyapatite may leave fluorapatite
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6
Q

How does fluoride aid remineralisation?

A
  • apatite dissolves in acidified plaque fluid
  • raises calcium, phosphate and fluoride local concentrations - fluoride ions in plaque contribute
  • fluoridated apatite (FHA) forms - common ion effect
  • low solubility and precipitates
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7
Q

Practical applications of the remineralisation theory

A
  • use fluoride toothpastes to build up local concentrations of fluoride
  • acidulated phosphate fluoride treatment
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8
Q

Fluoride inhibits bacteria what?

A

metabolism

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9
Q

How does fluoride inhibit bacterial metabolism?

A
  • fluoride uptake by bacteria higher at acid pH - pK of hydrofluroic acid is 3.45
  • pH of plaque fluid during cariogenic challenge is lowered (more acidic)
  • low pH favours formation of HF, which is taken up by bacteria by simple diffusion
  • bacterial cytoplasm pH is almost neutral which favours dissociation of HF
  • causes reduction in cytoplasmic pH and releases fluoride ions which bind to magnesium and inhibit enolase among others
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10
Q

Resistance to fluoride

A
  • generally resistant strains of bacteria haven’t been found clinically
  • some F-resistanrt S.mutans strains have been selected in lab (resistance mechanism not clear, probably multiple things)
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