Molecular Structure of Enamel Mineral (Amaechi 4) Flashcards
Concentration of minerals in enamel varies between ____, ___, and ______.
Persons, teeth, parts of the same tooth
Molecular structure of HA
10 Calcium ions, 6 Phosphate ions, 2 Hydroxyl ions
Distinction between the two Ca positions occurs b/c the
_____ and the _____ Ca ions are surrounded by
different kinds and numbers of other ions.
Columnar and Triangular
The PO4 ions occupy the bulk of the unit cell, giving the surface of the hydroxyapatite a net _____ charge
negative
The surface charge of the apatite crystals accounts for the following qualities of the enamel crystals:
- Strong ______ ability of the apatite
- Presence of large number of adsorbed ______ in the apatite
- Selective nature of the proteins of the ______
- Ion-exchange
- trace elements
- acquired salivary pellicle
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.
Stoichiometry
The reasons for this nonstoichiometric characteristics are believed to be due to:
- the large number of internal ______ that are tolerated by the hydroxyapatite crystals
- surface ______
- The presence of ______ apatites
- substitutions
- adsorption
- mineral deficient
HA is deficient in ___, ___, and ___.
Ca2+, PO43-, OH-
Enamel of teeth is not pure HA. It is usually _____-substituted and contains ____, ______, and _____.
- Carbonate
- HPO4
- Trace elements
- H2O
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?
Isomorphic substitution
Na+ or Mg2+ or Sr2+ may substitute for ____.
Ca2+
CO32 may substitute for ____.
PO43-
CO32- or F- may substitute for _____.
OH-
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.
different charge or size
The major impurities in both dentin and enamel mineral are…
- Carbonate
- Magnesium
- Sodium
Formation of fluorapatite is formed by replacement of the ______ by fluoride ions, which are smaller therefore resulting to decrease in a-axis dimension.
dipolar OH- groups
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.
calcium
Fluoride ions can also be incorporated into the crystal by formation of ______ with neighboring OH- ions.
hydrogen bond (OH-F)
Effects of Fluoride incorporation: Improvement in the crystallinity of the apatite by…
- increased stability of the ______.
- reduction in the number of ______ and ______ within the crystals
The net effect is _______.
- lattice structure
- imperfections and dislocations
-low acid solubility (decreased rate of demineralization)
Carbonated hydroxyapatite is formed when Carbonate is incorporated into the apatite by substitution for ________.
either 1 PO4 and/or 2 OH-
Incorporation of CO3 causes decrease in ___-axis but increase in ___-axis
- A
- C
Incorporation of CO3 causes disruption in the
reactions that normally stabilize the apatite
structure, resulting to apatite ____ stable than
pure hydroxyapatite.
less
Biological apatites are not pure HA. They are usually carbonate-substiuted and calcium deficient, poorly ____, and contains a ____, usually amorphous Ca-phosphate (ACP).
- Crystalline
- 2nd phase
The Major aspects of the structure and organization of the apatite crystal which influence its rate of dissolution (development of dental caries) are ______ and _____.
Composition and Crystallinity
Composition includes presence of ______.
Lattice impurities
Crystallinity includes the crystal ____, _____ (strains and lattice dislocations), and rate of _____ of dissolving ions through intercrystalline spaces.
- Size
- Defects
- Diffusion
Affected by substitution:
- Dissolution increase…
- Dissolution decreased…
- Carbonate (CO3- -), Strontium (Sr + +), Magnesium (Mg+ +)
- Fluoride (F-)
When can ion substitution occur?
- Pre-eruption
- Post-eruption
Pre-eruption
ionic exchange and equilibration
with tissue fluids
Post-eruption
ionic exchange and
equilibration with saliva, crevicular fluid & ingested fluids
