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Module 4 - Saliva > Biological mineralisation > Flashcards

Biological mineralisation Flashcards

1
Q

what is the structure of hydroxyapatite?

A

OH- ion surrounded by 3 Ca2+ ions
surrounded by 3 PO43-ions
enclosed by 6 Ca2+ ions

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2
Q

what happens to hydroxyapatite when fluoride is introduced?

A

F- may replace the OH-
Stabilises the lattice
= fluorapatite

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3
Q

what is the critical pH when apatite dissolves in hydroxyapatite and fluorapatite?

A

hydroxyapatite - 5.5
fluorapatite - 4.5

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4
Q

what are the theories of mineralisation?

A

alkaline phosphatase hypothesis
homogenous nucleation
heterogenous nucleation

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5
Q

what is the alkaline phosphatase hypothesis?

A

alkaline phosphatase enzyme hydrolyses organic phosphates and releases inorganic phosphates

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6
Q

what are the problems with the alkaline phosphatase hypothesis?

A
  • Organic phosphates too low to be an effective source.
  • Other sites contain alkaline phosphatase e.g., kidney.
  • Normal serum (phosphate) is sufficient.
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7
Q

what is homogenous nucleation?

A

the formation of a 1st solid from a solution of ions in which no solid previously existed
- serums contain Ca2+ and PO43- (tissue fluid) can form hydroxyapatite crystals

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8
Q

what is the issue with homogenous nucleation as a theory?

A

In a supersaturated solution of Ca2+ and PO43_ hydroxyapatite crystallites do not form but can sustain crystal growth. Hydroxyapatite crystals do not form spontaneously in the bloodstream, ions in serum can sustain crystal growth.

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9
Q

what is heterogenous nucleation?

A

A foreign solid will assist nucleation of a crystal, especially If it has a similar lattice structure.

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10
Q

in heterogenous nucleation, what may act as an epitaxic agent for crystal formation?

A

organic matrix

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11
Q

what are possible heterogenous nucleators?

A

collagen
proteoglycans
lipids
phosphoproteins

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12
Q

what do matrix vesicles provide?

A

an ideal microenvironment for crystal formation and growth.

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13
Q

what do matrix vesicles contain?

A

high concentrations of Ca2+ and PO43- which are released into the extracellular tissue so crystals grow and rupture vesicle

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14
Q

what part of mineralisation are matrix vesicles involved in?

A

dentine

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15
Q

summaries mineralisation initiation?

A

heterogenous nucleation - epitactic properties of matrix
matrix vesicles help initiate initial mineralisation of dentine

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16
Q

summarise subsequent mineralisation?

A

heterogenous nucleation
crystal growth in supersaturated serum

Module 4 - Saliva (7 decks)

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