Microbiology of dental caries

Question 1

Sequence to form plaque

Answer 1

2 seconds- Pellicle formation
1 minute- Pioneer bacteria
2 hours- Microcolonies and extracellular polysaccharide.
2 hours onwards- Biofilm development.
48 hours- Mature plaque

Question 2

Critical PH

Answer 2

The critical PH is 5.5- If it drops below 5.5 then the risk of decalcification increases.

Question 3

What do cavities need to form

Answer 3

For cavities to form there needs to be sucrose diet + specific bacteria.
Dental caries cant form with just sucrose diet.
Dental caries + surcose diet + antibiotics = no caries.

Question 4

On what areas of the do caries form on

Answer 4

Fissure caries - 99%
Approximal caries- 5-60%
Smooth surface caries- 5%

Question 5

How much do mutans streptococci increase before and during incipient phase

Answer 5

Mutans streptococci increase by 10-100 fold during incipient phase (white spot phase)

Question 6

At what stage of caries development is Lactobacilli found

Answer 6

Lactobacilli in developed caries only

Question 7

Root surface caries

Answer 7

Root surface caries are usually found in older patients with gingival recession and decreased salivary flow and has a higher critical PH level of 6.7.

Question 8

Mutans streptococcus

Answer 8

Isolated only from tooth surface, they are highly acidogenic and cariogenic.
There is less than 1% mutans streptococcus found in non-carious plaque.
There is 5-10% of bacteria from non-carious plaque.
Mutans streptococcus only colonise on hard non-shedding surfaces and are found more in stagnant or retentive sites.
Mutans streptococcus are most commonly acquired from primary caregivers.

Question 9

Virulence factors

Answer 9

1. Extracellular polysaccharide production.
   -Sucrose dependent.
   -Two types of polysaccharides.
   -Glucans.
   -Fructans.
2. Carbohydrate Fermentation
   -Ferments virtually all dietry
   simple sugars.
   -Very efficient sugar uptake system.
   -High fermentation rate compared to other streptococci and actinomyces.
   3.Aciduric
   -Survive relatively low PH
   -Fermentation at PH 5.5
   -Due to efficient proton extrusion
   4.Intracellular Polysaccharide storage.
   -Glycogen like polysaccharide
   -Facilitates prolonged fermentation in absence of exogenous carbohydrate.