CON05-2003 Fluoride & caries

Question 1

What is the principal mineral of enamel and dentine?

Answer 1

hydroxyapatite

Question 2

How is fluoride incorporated into the tooth at the pre eruptive stage?

Answer 2

Fluoride is incorporated during mineralisation

The fluoride comes from the tissue fluid on the maturing enamel surface to produce a surface effect

Question 3

How is fluoride incorporated into the tooth at the post eruptive stage?

Answer 3

Produces a surface effect only

The fluoride comes from saliva and fluoride containing products

Question 4

What do impurities in the enamel apatite contain?

Answer 4

Fluoride and carbon

Question 5

What happens to fluoride in the tooth?

Answer 5

It is firmly bound to substances within the tooth to form fluorohydroxyapaptite
It is loosely bound as calcium fluoride
Some fluoride is absorbed onto apaptite

Question 6

How does the solubility of fluorohydroxyapatite compare to that of hydroxyapatite?

Answer 6

Fluorohydroxyapaptite has a lower solubility than hydroxyapaptite so a lower pH is needed to cause demineralisation

Question 7

What concentration is fluoride within plaque?

Answer 7

5-10ppm

Question 8

Look at the graph on document. What occurs when the concentration of salivary calcium intersects the curve?

Answer 8

It is the critical pH and where dissolution takes place

Question 9

What happens to the critical pH, if the patient has more salivary calcium?

Answer 9

Critical pH is lower

Question 10

What is the critical pH specific to?

Answer 10

The hydroxyapatite crystal at a specific calcium ion concentration

Question 11

How does the critical pH change, when there is fluoride rich apatite at the same salivary calcium concentration?

Answer 11

Critical pH is lower

Question 12

Why is the critical pH lower in substituted fluoride apatite?

Answer 12

mineral can tolerate more acid before it dissolves

Question 13

How does calcium fluoride affect the tooth?

Answer 13

It acts as a reservoir of fluoride for the tooth
CaF2 is only formed with high concentrations of fluoride solutions to form globules
These globules have protein and phosphate rich surfaces
This reduces the rate of dissolution

Question 14

How does fluoride cause remineralisation?

Answer 14

It binds free floating calcium and phosphate ions from the acid attack and promotes reprecipitation
Reprecipitation narrows pores in enamel
This affects the rate of acid diffusion into enamel
It also affects the loss of dissolved ions

Question 15

What is fluoride release dependant on?

Answer 15

pH

Question 16

What is the antibacterial effect of fluoride?

Answer 16

Fluoride can inhibit carbohydrate metabolism of oral streptococci and lactobacilli
To do this, fluoride enters the bacteria and effects the enzymes in it and transport systems involved in carbohydrate metabolism

Question 17

How does fluoride get into bacteria?

Answer 17

Fluoride diffuses as HF into the cell
Low external pH promotes the formation of more HF
Higher intracellular pH of bacteria promotes the production of free H+ and F- ions
This allows more HF to enter

Question 18

What are the effects of fluoride on bacteria?

Answer 18

Enolase inhibitor
Intereferes with the PEP phosphotransferase system
Acidifcation of bacteria
High intracellular H+ concentration

Question 19

How does fluoride interfere with PEP phosphotransferase?

Answer 19

Bacteria needs PEP from glycolysis to work
PEP concentration is reduced by enolase inhibition
This results in less sugar uptake

Question 20

How does fluoride cause acidification of bacteria?

Answer 20

Dissociation of HF

Question 21

What does a high intracellular H+ concentration of bacteria cause?

Answer 21

Inhibits enolase
Reduces pH gradient between extraceullar and intracellular environments
Reduces hydrogen- sugar transport that would occur at pH 5.5

Question 22

What is fluorides effect on plaque?

Answer 22

Fluoride has no effect on bacterial adherence and initial plaque formation
Fluoride reduces acid production in plaque

Question 23

How does fluoride impair growth of apatite crystals?

Answer 23

It retains matrix proteins through binding of mineral to matrix proteins