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2ND YR- CSA - Chemistry lecs > THE CHEMISTRY OF ENAMEL CARIES > Flashcards

THE CHEMISTRY OF ENAMEL CARIES Flashcards

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1
Q

Under what conditions will ionic materials precipitate?

A

If the surrounding solution is above the saturation point

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2
Q

Under hat conditions will ionic materials dissolve?

A

If he surrounding solutions below the saturation point

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3
Q

When is saturation achieved|?

A

when the solubility product reaches a certain value

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4
Q

What is the solubility product for a binary salt XY?

A

Ksp={X}{Y}

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5
Q

What is the chemical formula for calcium hydroxyapatite?

A

Ca10(PO4)6(OH2

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6
Q

What is the solubility product for calcium hydroxyapatite?

A

Ksp = [Ca]^10 x [PO4]^6 x [OH]^2

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7
Q

If the supernatant is not supersaturated with respect to the hydroxyapatite what will happen?

A

Dissolution will occur

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8
Q

Give an example of dissolution in dentistry?

A

Caries and bone resorption

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9
Q

In the case go hydroxyapatite what can change the nature oft he phosphate anion?

A

The pH

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10
Q

What is the solubility product?

A

The solubility of a substance that can be split into separate ions is the solubility product?

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11
Q

What letters do we use to represent eh solubility product?

A

Ksp

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12
Q

Ksp is the product of what?

A

The concentration (mol/L) of the component ions raised to the appropriate power in. saturated solution

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13
Q

How calcium hydroxyapatite what increases the solubility product?

A

The carbonate and magnesium increases the solubility product

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14
Q

What happens if the solubility product of calcium hydroxyapatite increases?

A

Demineralisation occurs

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15
Q

What can we add to calcium hydroxyapatite to decrease the solubility product?

A

Fluoride

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16
Q

At low pH levels describe the concentration calcium hydroxyapatite?

A

The plaque fluid may be undersaturated with respect to enamel hydroxyapatite but supersaturated with respect to fluroapatite

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17
Q

Is fluroapaptite more or less soluble comparison to calcium hydroxyapatite?

A

Less soluble

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18
Q

State the chemical formula of fluroapaptite

A

Ca10(PO4)6F2

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19
Q

What is critical in understanding enamel/ apatite dissolution?

A

Ionisation of the phosphate ion

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20
Q

How do phosphate salts form?

A

When positively charged ions attach to the negatively charged oxygen atoms of the phosphate ions forming an ionic compound

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21
Q

State the positive ion fund in calcium hydroxyapatite

A

Ca2+

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22
Q

Name the different forms inorganic phosphate is preset in a fluid

A

H3PO4
(H2PO4)–
(HPO4)2–
(PO4)3–

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23
Q

What determines the concentration and proportion of the different forms of inorganic phosphate ions in fluid?

A

The pH

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24
Q

If theres a low pH which inorganic phosphate will be present in the highest proportion?

A

H3PO4

25
Q

Increasing the Ph of saliva increases the concentration of which inorganic phosphate?

A

(PO4)3-

26
Q

Blow what pH does dissolution occur?

A

Below a pH OF 5.5

27
Q

Why does dissolution occur below a pH of 5.5?

A

As theres more (H2PO4)- than (HPO4)2- ions

28
Q

Above pH 5.5 name the dominant phosphate ion

A

(HPO4)2-

29
Q

Below pH 5.5 name the dominant phosphate ion

A

(H2PO4)-

30
Q

What does the critical pH depend on?

A

The pKa of the phosphate ion in solution and the pKa of the phosphate ion in the crystal surface

31
Q

Name the (H2PO4)- ion

A

Dihydrogen phosphate

32
Q

What happens to enamel below a pH of 5.5?

A

Demineralisation occurs

33
Q

Describe what happens to inorganic phosphate ions as protons are dded?

A

H+ binds to (PO4)3- ions graduallyrednucinthe ionic binding of these ion to the Ca2+ ions in hydroxyapatite crystals

34
Q

What are protons?

A

Hydrogen ions (H+)

35
Q

What causes the decrease in pH in our mouths?

A

Fermentation of sugars by bacterial

36
Q

If the pH is higher than 4.5 and fluoride is present what happens?

A

The biofilm fluid is supersaturated with respect to fluorapatite and there is a re-precipitation of minerals in the enamel

37
Q

As well as pH what dos th solubility of hydroxyapatite depend on?

A

The ionic levels of the hydroxyapatite components of the surrounding medium

38
Q

After the exposure to sugars has stopped what happens in the biofilm?

A

Acids in the biofilm are cleared by saliva and converted to salts
This increases the pH again

39
Q

Describe he biofilm fluid at pH higher than 5.5

A

The biofilm fluids supersaturated with respect to hydroxyapatite and fluroapatite

40
Q

Why is fluid being supersaturated with respect to hydroxyapatite and fluroapatite beneficial to enamel?

A

Ad calcium and phosphate lost by enamel can be more effective recovered if fluoride is still present in the biofilm

41
Q

Clinically, describe how early caries lesion are seen

A

As white spot lesions on the tooth surface

42
Q

What are white spot lesions caused by?

A

Dissolution by acid produced byroad bacterial

The acid produces tiny pored which dry out producing white spots due to light scatter

43
Q

Describe the surface beneath white spot lesions

A

There is increases porosity beneath the surface ad underlying dentine MAY be affected

44
Q

Name the 3 layers that can be affected by caries (starting with the innermost layer)

A
  1. Translucent zone
  2. Dark zone
  3. Body of the lesion
45
Q

Describe the pores in the translucent zone

A

Relatively late and pores of uniform size

46
Q

Describe the pores in the dark zone

A

Increased porosity but also small pores present that are inaccessible to the imbibing fluid

47
Q

Describe the pores in the body of the lesion

A

Very porous with very large pores

48
Q

Which mineral is lost from the translucent layer the most when a carious lesion forms?

A

Magnesium and carbonate

49
Q

Which mineral is lost from the dark layer the most when a carious lesion forms?

A

Magnesium

50
Q

The concentration of which mineral increases when a carious lesion forms?

A

Fluoride as it accumulates where there is a carious lesion

51
Q

Name the first mineral removed from enamel when carious lesion forms

A

Soluble carbonate and magnesium rich components

52
Q

Why is the removal of carbonate and magnum during early caries formation beneficial?

A

Loss of these destabilising ions moves the supernatant in the enamel towards precipitation of carbonate and magnesium depleted mineral
Thus precipitation occurs on the dark zone

53
Q

How and where is magnesium thus to be located in enamel?

A

Either on crystal surfaces or in separate more acid soluble phases

54
Q

What is enamel built from/

A

Enamel prisms

55
Q

What are enamel prisms comprised of?

A

Millions of hydroxyapatite crystallites

56
Q

The presence of enamel prisms does what to the overall enamel structure?

A

Creates a mechanically strong structure BUT the structure is vulnerable from a chemical POV

57
Q

Te porosities present in the enamel structure mean what can happen?

A

The weak organic acids formed in the dental biofilm will penetrate into enamel rather than dissolve the enamel layer by layer

58
Q

Describe the way acid penetrates into the tooth?

A

Penetration of acids will lead to selective dissolution inside the tooth,
Surface layer is generally being bypassed as this is less soluble due to the accumulation of fluoride.

2ND YR- CSA - Chemistry lecs (3 decks)

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