Plaque and dental caries

Question 1

Describe what is meant by biofilm.

Answer 1

Layers of bacteria living symbiotically/tolerably

Question 1

Define plaque.

Answer 1

The complex microbial community found on the tooth surface embedded in a matrix of polymers of bacterial and salivary origin. It is made of layers

Question 2

What is the make-up of plaque?

Answer 2

80-90% metabolising bacteria
10-20% intermicrobial matrix (polymers)

Question 3

What is an ecological determinant of plaque?

Answer 3

Adherence to specific molecules in the acquired pellicle.

Question 4

How long does it take for the acquired salivary pellicle to form after saliva exposure?

Answer 4

2 seconds

Question 5

Describe the aetiology of plaque (4 steps)

Answer 5

• After 1 minute primary colonisation takes place, pioneer bacteria such as strep sanguinis
• After 2 hours biosynthesis of extracellular matrix occurs (biofilm development)
• After 2+ hours secondary colonisation is promoted by extracellular matrix
• After 48 hours formation of a highly complex microbial community has occured- mature plaque

Question 6

What mediates microbial attachment making it stronger?

Answer 6

extracellular polysaccharide (insoluble, produced by streptococci, actinomyces)

Question 7

What are some nutrient sources for oral bacteria? (4)

Answer 7

• Host diet
• Oral secretions
• Other bacteria
• Dead or damaged host cells

Question 8

Describe supragingival plaque.

Answer 8

• Caries causing
• > 90% gram +ve
• Cocci and filamentous
• Carbohydrate fermenters (acidogenic)
• Microaerophilic- prefer lower oxygen

Question 9

Describe subgingival plaque.

Answer 9

• Periodontal disease causing
• > 50% gram -ve
• Rods and fusiforms
• Proteolytic- stinky
• Anaerobic

Question 10

Define dental caries.

Answer 10

The localised destruction of the tissues of the tooth by bacterial fermentation of dietary carbohydrates (produces acids) -> decalcification ->dissolution of softened residue

Question 11

At what pH does decalcification of enamel occur?

Answer 11

<5.5

Question 12

What are 4 methods of preventing dental caries?

Answer 12

• Reducing carbohydrate in saliva
• Increase tooth resistance to acid attack (fluoride)
• Reduce tooth susceptibility (fissure sealants)
• Reduce or eliminate cariogenic microorganisms (antimicrobial agents)

Question 13

Describe mutans streptococci (6 points)

Answer 13

• a group of 7+ species
• Highly acidogenic/cariogenic
• Only colonise hard non-shedding surfaces
• Found more often in retentive sites
• Production of adherent extracellular polysaccharides
• most commonly acquired from primary caregiver

Question 14

Name the four cariogenic attributes of mutans streptococci

Answer 14

• Acididuric
• Ferment virtually all dietary simple sugars
• Extracellular polysaccharide production
• Intracellular polysaccharide storage

Question 15

Describe the aciduric property of mutans streptococci

Answer 15

• Mutans streptococci can survive a relatively low pH which allows the bacteria to continue to produce acid and attack the tooth surface.
• Fermentation at pH 5.5

Question 16

Describe the extracellular polysaccharide production property of mutans streptococci.

Answer 16

• Two types, glucans and fructans
• Allows organisms to stick to surfaces or other bacteria
• If strep mutans doesnt stick to anything it cant cause disease
• Prevents diffusion of minerals into and out of plaque- calcium ions blocked from remineralising enamel

Question 17

Describe the carbohydrate fermentation property of mutans streptococci.

Answer 17

• Ferment virtually all dietary simple sugars -> produces a lot of acid!! (acidogenic)(not mannitol and sorbitol)
• Due to efficient sugar uptake system
• Principally produces lactic acid
• Coupled with a high fermentation rate as opposed to other streptococci

Question 18

Describe the intracellular polysaccharide storage property of mutans streptococci.

Answer 18

• Glycogen like polysaccharide
• Essentially a reserve of sugar to make more acid
• Facilitates prolonged fermentation (acid production) in the absence of exogenous carbohydrate. Similar to glycogen storage in muscles

Question 19

What is the significance of sucrose in dental caries?

Answer 19

• Sucrose drives glucose polymerisation by glucosyl transferase (makes glucans and fructans)
• Sucrose can be fermented by cariogenic bacteria such as strep. mutans
• Sucrose is involved in the virulence factors of mutans streptococci