ICP L5: Biochemical events in dental plaque

Question 1

What causes caries

Answer 1

Bacteria in the mouth which produce acids which lowers the pH causing demineralisation and this leads to caries over time

Question 2

What are the risk factors for caries

Answer 2

• orthodontic appliances
• xerostomia
• gum tissue recession
• radiation therapy
• smokeless tabacco
• XS alcohol consumption causing xerostomia
• poor oral hygine

Question 3

What is plaque

Answer 3

Aggregation of bacteria and products onto the tooth surface

Question 4

What is the aquired pellicle

Answer 4

Salivary components adsorbed onto HAP surface which is composed of protectant salivary glycoproteins which protects the enamel and provides lubrication

Question 5

Briefly outline stages in oral biofilm formation

Answer 5

1. Adhesion
2. Colonisation
3. Coadhesion
4. Maturation and detachment

Question 6

How does the adhesion of bacteria to enamel occur

Answer 6

Via the pellicle which has specific receptors to certain proteins within the biofilm

Question 7

Describe plaque composition

Answer 7

50% = bacterial and salivary protein 
20-30% = carbohydrates and lipids
25% = inorganic components (Ca, P greater than in saliva) K, Na, Mg, F

Question 8

What determines the rate of enamel dissolution and remineralisation

Answer 8

Most Ca is non-ionic, but this becomes ionised as the pH drops and determines the rate of these two events

Question 9

What is plaque fluid

Answer 9

This is the extracellular aqueous phase of dental plaque providing aqueous medium for diffusion and exchange of substances between saliva and tooth surface

Question 10

What is the main acid involved in caries formation

Answer 10

Lactic acid

Question 11

What is shown by the Stephan curve

Answer 11

How the salivary pH changes after a glucose challange; this response is dependant on the bacterial colonies present

Question 12

What contributes to the extent of pH drop after a glucose challange

Answer 12

1. Type and amount of CHO (sugars) avaliable
2. Bacteria present
3. Salivary composition and flow rate
4. Other foods ingested
5. Thickness and age of dental plaque (after last clean)

Question 13

What is the resting plaque pH of someone who is caries-prone

Answer 13

Normal = pH ~ 6.5 - 7
Risk = <6.5

Question 14

What contributes to the differences in resting plaque

Answer 14

Bacterial composition affects the metabolic properties of plaque; when the host doesn’t eat cariogenic bacteria still produce acids from storage carbohydrates

Question 15

What type of sugars have the greatest caries promoting potential

Answer 15

Monosaccharides

Question 16

Why are sugar alcohols better than monosaccharides and disaccharides

Answer 16

Because bacteria cannot convert these sugars into acids and so they are not caries promoting - thus these could be used as a sugar replacement

Question 17

What can prevent lactic acid production

Answer 17

Inhibition of the enzymes involved in glycolysis

Question 18

Give examples of cariogenic bacteria

Answer 18

1. Streptococci (S. mutans); gram positive, sucrose, fissures
2. Actinomyces; gingival plaque, gingivits
3. Lactobacilli spp; produce lactic acid and acetate, results in caries and requires sucrose

Question 19

What is the risk of frequent sugar intake

Answer 19

Changes the local environment so there is a shift in balance of plaque microflora due to the repeated low pH

This favours the growth of cariogenic species

Results in dental caries

Question 20

Define acidogenicity

Answer 20

The ability to produce acid rapidly from fermentable carbohydrate

Question 21

Define aciduricity

Answer 21

The ability to survive and continue to produce acid at acidic pH

Question 22

Why is production of extracellular polysaccharises from dietary sucrose important for plaque formation

Answer 22

Because it facillitates adherance to tooth surfaces and build up of large bacterial deposits

Question 23

Why is production of intracellular polysaccharises important for plaque formation

Answer 23

As storage components to prolong acid formation and acidic pH

They provide energy for ATPase which drives protons out of the cell and so adapts to low pH environment

Question 24

How is the optimum intracellular pH maintained for caries production

Answer 24

1. Low proton permeability of cell membrane; cell wall thickens
2. Production of bases
3. Buffering capacity of the cytoplasm
4. Active transport of protons out of hte cell

Question 25

What is the role of glucas

Answer 25

Major component of interbacterial matrix acting as a barrier to the outward diffusion of acids from plaque

They may serve as carbohydrate stores and this is for a longer duration than with fructans

Question 26

What happens in the alkalisation phase of plaque pH

Answer 26

• acid diffusion
• buffering capacity
• alkali from bacterial metabolism

Ammonia / CO2 are the end products from alkali generation