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Exam 2: DHHD 5001 > Molecular Structure of Enamel Mineral (Amaechi 4) > Flashcards

Molecular Structure of Enamel Mineral (Amaechi 4) Flashcards

1
Q

Concentration of minerals in enamel varies between ____, ___, and ______.

A

Persons, teeth, parts of the same tooth

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2
Q

Molecular structure of HA

A

10 Calcium ions, 6 Phosphate ions, 2 Hydroxyl ions

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3
Q

Distinction between the two Ca positions occurs b/c the
_____ and the _____ Ca ions are surrounded by
different kinds and numbers of other ions.

A

Columnar and Triangular

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4
Q

The PO4 ions occupy the bulk of the unit cell, giving the surface of the hydroxyapatite a net _____ charge

A

negative

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5
Q

The surface charge of the apatite crystals accounts for the following qualities of the enamel crystals:

  1. Strong ______ ability of the apatite
  2. Presence of large number of adsorbed ______ in the apatite
  3. Selective nature of the proteins of the ______
A
  • Ion-exchange
  • trace elements
  • acquired salivary pellicle
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6
Q

Hydroxyapatite crystals lack _______. The measured concentration of the chemical constituents
in the enamel crystals is different from that predicted by the formula for hydroxyapatite, Ca10(PO4)6(OH)2.

A

Stoichiometry

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7
Q

The reasons for this nonstoichiometric characteristics are believed to be due to:

  1. the large number of internal ______ that are tolerated by the hydroxyapatite crystals
  2. surface ______
  3. The presence of ______ apatites
A
  1. substitutions
  2. adsorption
  3. mineral deficient
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8
Q

HA is deficient in ___, ___, and ___.

A

Ca2+, PO43-, OH-

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9
Q

Enamel of teeth is not pure HA. It is usually _____-substituted and contains ____, ______, and _____.

A
  • Carbonate
  • HPO4
  • Trace elements
  • H2O
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10
Q

What property allows cations and anions of similar size or charge to the ions in the hydroxyapatite may substitute for them on the surface and the interior of the crystal?

A

Isomorphic substitution

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11
Q

Na+ or Mg2+ or Sr2+ may substitute for ____.

A

Ca2+

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12
Q

CO32 may substitute for ____.

A

PO43-

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13
Q

CO32- or F- may substitute for _____.

A

OH-

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14
Q

In most of these cases, the impurity ion has a ________ to the ion it is replacing. This results in misfits in the crystal lattice which disturb the crystal structure and in turn make the mineral chemically less stable: in other words more soluble.

A

different charge or size

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15
Q

The major impurities in both dentin and enamel mineral are…

A
  • Carbonate
  • Magnesium
  • Sodium
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16
Q

Formation of fluorapatite is formed by replacement of the ______ by fluoride ions, which are smaller therefore resulting to decrease in a-axis dimension.

A

dipolar OH- groups

17
Q

The fluoride ion in the center of calcium triangle also forms strong interaction forces with _____ resulting to a decrease in Ca to anion and Ca to Ca distances which also contributes to decrease in a-axis.

A

calcium

18
Q

Fluoride ions can also be incorporated into the crystal by formation of ______ with neighboring OH- ions.

A

hydrogen bond (OH-F)

19
Q

Effects of Fluoride incorporation: Improvement in the crystallinity of the apatite by…

  1. increased stability of the ______.
  2. reduction in the number of ______ and ______ within the crystals

The net effect is _______.

A
  1. lattice structure
  2. imperfections and dislocations

-low acid solubility (decreased rate of demineralization)

20
Q

Carbonated hydroxyapatite is formed when Carbonate is incorporated into the apatite by substitution for ________.

A

either 1 PO4 and/or 2 OH-

21
Q

Incorporation of CO3 causes decrease in ___-axis but increase in ___-axis

A
  • A

- C

22
Q

Incorporation of CO3 causes disruption in the
reactions that normally stabilize the apatite
structure, resulting to apatite ____ stable than
pure hydroxyapatite.

A

less

23
Q

Biological apatites are not pure HA. They are usually carbonate-substiuted and calcium deficient, poorly ____, and contains a ____, usually amorphous Ca-phosphate (ACP).

A
  • Crystalline

- 2nd phase

24
Q

The Major aspects of the structure and organization of the apatite crystal which influence its rate of dissolution (development of dental caries) are ______ and _____.

A

Composition and Crystallinity

25
Q

Composition includes presence of ______.

A

Lattice impurities

26
Q

Crystallinity includes the crystal ____, _____ (strains and lattice dislocations), and rate of _____ of dissolving ions through intercrystalline spaces.

A
  • Size
  • Defects
  • Diffusion
27
Q

Affected by substitution:

  • Dissolution increase…
  • Dissolution decreased…
A
  • Carbonate (CO3- -), Strontium (Sr + +), Magnesium (Mg+ +)

- Fluoride (F-)

28
Q

When can ion substitution occur?

A
  • Pre-eruption

- Post-eruption

29
Q

Pre-eruption

A

ionic exchange and equilibration

with tissue fluids

30
Q

Post-eruption

A

ionic exchange and

equilibration with saliva, crevicular fluid & ingested fluids

Exam 2: DHHD 5001 (14 decks)

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