Dental Plaque

Question 1

What are the early colonisers in dental plaque?

Answer 1

S. mitis group (S. mitis, S. sanguis, S. oralis)

Question 2

What is the timeframe of plaque maturation?

Answer 2

• After 7 days strep still dominant

- After 14 days only 15% strep, anaerobic rods and filaments dominate

Question 3

What are cryptitopes?

Answer 3

Hidden binding sites that bacteria can attach to after it is exposed (e.g. after enzyme action removes component to expose binding site)

Question 4

What bacterial species is the main co-aggregator?

Answer 4

Fusobacterium nucleatum

Question 5

What linkages for EPS are soluble and insoluble? Why do bacteria use both? Give an example for each.

Answer 5

a1-6 = soluble (Glucans - used to form water channels)

a1-3 or a1-4 = insoluble (Mutan - resists being washed away)

Question 6

What are THREE beneficial and THREE antagonistic microbial interactions in biofilm.

Answer 6

Beneficial

• Enzyme complementation
• Food web (ie. feed off each others byproducts)
• Co-aggregation

Antagonistic

• Nutrient competition
• pH extremes
• Bacteriocins

Question 7

What are the FIVE Koch’s Postulates for plaque derived diseases?

Answer 7

1. Microbe should be present in sufficient numbers to initiate disease
2. Microbe should cause increased levels of specific antibodies
3. Microbe should possess suitable virulence factors
4. A pure culture should be able to cause the disease in a suitable animal model
5. Elimination of the microbe should result in clinical improvement

Question 8

What bacteria are prevalent in early demin lesions? Which bacteria comes later, and why?

Answer 8

• S. mutans and A. naeslundii

- Lactobacilli come later (poor attachment to tooth surface)

Question 9

Why is S. mutans much better at attaching to tooth structure vs. Lactobacilli?

Answer 9

S. mutans has three different kinds of extracellular Glucosyltranserase (GTF) which produce glucans to aid in attachment.

Question 10

How is S. mutans aciduric and acidogenic?

Answer 10

• Aciduric because it has high level of membrane bound ATPase activity with optimal pH lower than others
• Acidogenic because it shuts off PTS system and uses homofermentation in high nutrient conditions (producing the strong lactic acid)

Question 11

What are FOUR important pathogenic determinants of bacteria and THREE less important ones.

Answer 11

Important

• GTF (attachment/colonisation)
• IPS production (intracellular glycogen)
• Lactate dehydrogenase (lactic acid production)
• Aciduricity (withstand lower pH)

Less important
- Fructosyltransferase (fructan - extracellular food)
- Antigen I/II (attachment)
- PTS (sugar transport in low sugar condns “teaspoon”)
NOTE: Multiple sugar TS more important “shovel”

Question 12

What are THREE important ways in which fluoride is antagonistic against S. mutans?

Answer 12

• Inhibit glycolysis (inhibit enolase)
• Acidifies internal pH
• Reduces IPS synthesis

Question 13

What is one unique way xylitol antagonises S. mutans?

Answer 13

S. mutans engages in a futile cycle with xylitol, spending ATP to bring it in only to realise it cannot use it, so it spends ATP pumping it out, but then takes it in again with ATP.

Question 14

Describe the changes in microbiology from health to gingivitis.

Answer 14

Streptococci -> Actinomyces naeslundii/israelii (non-bleeding stage) -> black pigmented anaerobes like p.gingivalis (bleeding stage)

Question 15

True or false: Nutrient supply to bacteria increases during gingivitis.

Answer 15

True, increased GCF flowrate provides bacteria with more nutrients.

Question 16

What are FOUR host biological features that may result in damage during periodontitis.

Answer 16

• More immune complexes (type III hypersensitivity)
• More complement (type II hypersensitivity)
• Prostaglandins (osteoclast activity)
• Macrophages (RoS)

Question 17

What is the acronym for bacterial pathogenicity?

Answer 17

AGED (Attachment, Growth, Evasion, Damage)

Question 18

Why might the red complex be particularly relevant in periodontitis?

Answer 18

• They produce a range of proteases.

Question 19

Give an example of AGED from P. gingivalis.

Answer 19

Attachment - has fimbrae
Growth - produces haemolysin (breaks down RBCs for iron)
Evasion - produces capsule
Damage - proteases (degrade collagen and host protease inhibitors)

Question 20

What bacteria do we mainly see subgingivally in periodontal lesions and why?

Answer 20

Usually gram -ve anaerobes that are asaccharolytic.

- This is because GCF provides lots of protein.

Question 21

Explain the pyramid diagram of bacteria in periodontal disease.

Answer 21

The top is the red complex (late colonisers), but they cannot exist with the lower tiers being there first (early and secondary colonisers).

Question 22

Which THREE viruses may be implicated in aggressive periodontal disease?

Answer 22

• EBV
• HSV
• Cytomegalovirus

Question 23

What are FOUR features of the microbiology seen in apical periodontitis?

Answer 23

• Restricted group of species (average 6 species)
• Mostly anaerobic
• Both gram +ve and -ve
• Fastidious nutritional requirements (pulp is rich in nutrients)

Question 24

What are THREE mechanisms of action for:

• Flouride
• Xylitol
• CHX

Answer 24

Fluoride
- Inhibit enolase (glycolysis)
- Reduce IPS (energy for acid prodn)
- Reduce EPS (plaque less sticky)
Xylitol
- Futile cycle (inhibit PTS system)
- Decrease aciduricity
- Decrease adherence
CHX
- Decrease adherence
- inhibit PEP-PTS
- interfere with ATPase (aciduricity)
- Detergent effect (damages membrane)