Dental Caries

Question 1

What are dental caries ?

Answer 1

A bacterial disease where bacteria on the tooth surface produces acid which erodes the enamel

Question 2

What is the consequences of dental caries ?

Answer 2

• inflammation of the pulp
• apical periodontis (most common cause of toothache)

Question 3

What is cariogenicity ?

Answer 3

A measure of a substances ability to cause dental caries

Question 4

What are the 4 variables which play a role in causing caries ?

Answer 4

• bacteria
• diet
• time
• susceptible surface

Question 5

What is the evidence for the involvement of bacteria in causing caries ?

Answer 5

Gnotobiotic animal experiment
- no matter what diet is fed to sterile animals they won’t develop any caries but as soon as bacteria is introduced they will develop caries

Question 6

What bacteria is present in the mouth ?

Answer 6

• various streptococci in the plaque
• lactobacillus in the saliva

Question 7

Which bacteria is responsible for plaque and caries ?

Answer 7

Streptococcus mutans

Question 8

Summarise bacterial metabolism

Answer 8

• sugar is a potential source of energy for bacteria
• starch, glucose, fructose and sucrose are all substrates for plaque bacteria
• monosaccharides and disaccharides are the preferred sugars because they are small so they can enter cells quickly and be degraded

Question 9

How do bacteria synthesise polysaccharides ?

Answer 9

• synthesise polysaccharides from simpler sugars
• store glucose intracellularly as glycogen
• streptococcus mutants also store polysaccharides extracellularly

Question 10

Which polysaccharides do streptococcus mutans store extracellularly ?

Answer 10

• dextrans
• levans

Question 11

Summarise the structure and properties of dextrans

Answer 11

• homopolymer of glucose
• polysaccharide of glucose through alpha 1-6 linkage
• big polysaccharide which is stored extracellularly
• sticky so can adhere to susceptible surfaces

Question 12

Summarise the structure and properties of levans

Answer 12

• polysaccharide of fructose through beta 1-2 linkage
• big polysaccharide stored extracellularly
• sticky so can adhere to susceptible surfaces

Question 13

How do dextrans and levans cause plaque formation ?

Answer 13

1) form a sticky environment so coat bacteria and the surface of the tooth
2) enable streptococci to adhere to one another and to the tooth surface
3) oxygen is excluded from the inside of this sticky voluminous mass
4) leads to plaque formation

Question 14

Production of energy from sugars

Question 15

Which acids are produced in the plaque fluid ?

Answer 15

• acetic acid
• propionic acid
• formic acid
• butyric acid
• lactic acid

Question 16

What is the concentration of lactic acid in the plaque fluid ?

Answer 16

• normally a minor component but increases greatly after ingestion of sucrose
• pre ingestion = 12 mMol/l
• post ingestion = 35 mMol/l

Question 17

What are the effects of plaque bacteria ?

Answer 17

• plaque bacteria produces proteolytic enzymes e.g. collagenases
• collagenases breakdown collagens
• leads to gum damage, reddening, bleeding and inflammation

Question 18

What is the biddy index ?

Answer 18

A measure of the cariogenicity of foods based on their sugar content and their retention time in the mouth

Question 19

Which sugar is at the top of the biddy index ?

Answer 19

Sucrose - so it is the worst sugar

Question 20

Why is sucrose the worst sugar ?

Answer 20

• the glucose fructose bond has a relatively high energy
• the glycosyltransferase enzyme of streptococcus mutans is able to utilise the energy from this bond to synthesise glucans without the need for other energy sources

Question 21

Why is chocolate less cariogenic than other sweets ?

Answer 21

It is thought to reduce calcium phosphate solubility and so it protects the enamel from acid attack

Question 22

What do Stephan curves show ?

Answer 22

The critical pH is 5.5 and it takes time for this pH to revert back to normal after eating
- if you snack between meals then you are not giving the mouth time to return to the normal pH and so there is an increased incidence of caries

Question 23

Why do some studies show that it is good to eat cheese at the end of a meal ?

Answer 23

It stimulates salivary flow and calcium lowers the solubility of apatite

Question 24

How can caries be prevented ?

Answer 24

• brushing to remove plaque
• inhibiting glycosyltransferase activity of S mutans which reduces the generation of sticky plaque
• using agents to solubilise polysaccharides so no anaerobic environment is created and so no acidic erosion of the teeth
• using fluoride products

Question 25

How does fluoride help to prevent caries ?

Answer 25

• systemic fluoride strengthens the teeth
• fluoride helps to remineralise the teeth by slowing down bacterial metabolism
• topical fluoride may kill decay causing bacteria