THE CHEMISTRY OF ENAMEL CARIES

Question 1

Under what conditions will ionic materials precipitate?

Answer 1

If the surrounding solution is above the saturation point

Question 2

Under hat conditions will ionic materials dissolve?

Answer 2

If he surrounding solutions below the saturation point

Question 3

When is saturation achieved|?

Answer 3

when the solubility product reaches a certain value

Question 4

What is the solubility product for a binary salt XY?

Answer 4

Ksp={X}{Y}

Question 5

What is the chemical formula for calcium hydroxyapatite?

Answer 5

Ca10(PO4)6(OH2

Question 6

What is the solubility product for calcium hydroxyapatite?

Answer 6

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

Question 7

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

Answer 7

Dissolution will occur

Question 8

Give an example of dissolution in dentistry?

Answer 8

Caries and bone resorption

Question 9

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

Answer 9

The pH

Question 10

What is the solubility product?

Answer 10

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

Question 11

What letters do we use to represent eh solubility product?

Answer 11

Ksp

Question 12

Ksp is the product of what?

Answer 12

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

Question 13

How calcium hydroxyapatite what increases the solubility product?

Answer 13

The carbonate and magnesium increases the solubility product

Question 14

What happens if the solubility product of calcium hydroxyapatite increases?

Answer 14

Demineralisation occurs

Question 15

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

Answer 15

Fluoride

Question 16

At low pH levels describe the concentration calcium hydroxyapatite?

Answer 16

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

Question 17

Is fluroapaptite more or less soluble comparison to calcium hydroxyapatite?

Answer 17

Less soluble

Question 18

State the chemical formula of fluroapaptite

Answer 18

Ca10(PO4)6F2

Question 19

What is critical in understanding enamel/ apatite dissolution?

Answer 19

Ionisation of the phosphate ion

Question 20

How do phosphate salts form?

Answer 20

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

Question 21

State the positive ion fund in calcium hydroxyapatite

Answer 21

Ca2+

Question 22

Name the different forms inorganic phosphate is preset in a fluid

Answer 22

H3PO4
(H2PO4)–
(HPO4)2–
(PO4)3–

Question 23

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

Answer 23

The pH

Question 24

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

Answer 24

H3PO4

Question 25

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

Answer 25

(PO4)3-

Question 26

Blow what pH does dissolution occur?

Answer 26

Below a pH OF 5.5

Question 27

Why does dissolution occur below a pH of 5.5?

Answer 27

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

Question 28

Above pH 5.5 name the dominant phosphate ion

Answer 28

(HPO4)2-

Question 29

Below pH 5.5 name the dominant phosphate ion

Answer 29

(H2PO4)-

Question 30

What does the critical pH depend on?

Answer 30

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

Question 31

Name the (H2PO4)- ion

Answer 31

Dihydrogen phosphate

Question 32

What happens to enamel below a pH of 5.5?

Answer 32

Demineralisation occurs

Question 33

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

Answer 33

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

Question 34

What are protons?

Answer 34

Hydrogen ions (H+)

Question 35

What causes the decrease in pH in our mouths?

Answer 35

Fermentation of sugars by bacterial

Question 36

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

Answer 36

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

Question 37

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

Answer 37

The ionic levels of the hydroxyapatite components of the surrounding medium

Question 38

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

Answer 38

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

Question 39

Describe he biofilm fluid at pH higher than 5.5

Answer 39

The biofilm fluids supersaturated with respect to hydroxyapatite and fluroapatite

Question 40

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

Answer 40

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

Question 41

Clinically, describe how early caries lesion are seen

Answer 41

As white spot lesions on the tooth surface

Question 42

What are white spot lesions caused by?

Answer 42

Dissolution by acid produced byroad bacterial | The acid produces tiny pored which dry out producing white spots due to light scatter

Question 43

Describe the surface beneath white spot lesions

Answer 43

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

Question 44

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

Answer 44

1. Translucent zone 2. Dark zone 3. Body of the lesion

Question 45

Describe the pores in the translucent zone

Answer 45

Relatively late and pores of uniform size

Question 46

Describe the pores in the dark zone

Answer 46

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

Question 47

Describe the pores in the body of the lesion

Answer 47

Very porous with very large pores

Question 48

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

Answer 48

Magnesium and carbonate

Question 49

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

Answer 49

Magnesium

Question 50

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

Answer 50

Fluoride as it accumulates where there is a carious lesion

Question 51

Name the first mineral removed from enamel when carious lesion forms

Answer 51

Soluble carbonate and magnesium rich components

Question 52

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

Answer 52

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

Question 53

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

Answer 53

Either on crystal surfaces or in separate more acid soluble phases

Question 54

What is enamel built from/

Answer 54

Enamel prisms

Question 55

What are enamel prisms comprised of?

Answer 55

Millions of hydroxyapatite crystallites

Question 56

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

Answer 56

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

Question 57

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

Answer 57

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

Question 58

Describe the way acid penetrates into the tooth?

Answer 58

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.