Microbiology of Dental Caries

Question 1

How many phylotypes colonize the oral cavity?

Answer 1

19000

Question 2

What are the features of dental biofilms?

Answer 2

It is highly organized

Planktonic bacteria leave or join the biofilm

Also has archaea, yeasts, parasites, and viruses

Question 3

What causes plaque-induced disease?

Answer 3

Shifts from symbiotic microbial relationships to dysbiosis responsible for initiating carious processes.

Ecological shift may facilitate acid production.

Question 4

How are plaque biofilms associated with the gingiva?

Answer 4

Gingivitis and periodontitis result from the host response to subgingival plaque biofilm

Question 5

What kind of interaction do streptococcus and candida have?

Answer 5

Streptococcus plaques and candida albicans can co-interact to increase the pathogenesis.

Question 6

What microorganisms cause primary enamel carious lesions?

Answer 6

Non-mutans streptococci and actinomyces

Acid production by streptococcus mutans and streptococcus sabrinus is higher than that of other oral streptococci.

Question 7

How much of the oral microbiota consists of strep mutans?

Answer 7

Strep mutans constitutes about 30% of the total microbiota and is less prevalent in progressing areas of dental caries.

Question 8

How does candida affect dental caries?

Answer 8

Can survive acidic conditions due to pH, secretes organic acids that decreases pH and provides adhesion sites for bacteria.

Streptococci excrete lactate which is useful for candida metabolism

Question 9

What does strep mutans do in dental caries?

Answer 9

Strep mutans is a major aetiological agent.

Mutans streptococci in plaque and saliva have been frequently isolated. Insoluble glucan formation, excessive acid production in response to sucrose containing diet.

Question 10

What do lactobacilli do to dental caries?

Answer 10

Lactobacilli could potentially have a suppressive effect on cariogenic streptococci but lactobacillus species have also been implicated as secondary pathogens in deep carious lesions.

Question 11

How are primary and secondary dentition different in terms of caries risk?

Answer 11

Healthy primary and permanent teeth harbour different supragingival microbial profiles in children.

Question 12

What are probiotics and how effective where they for preventing carious lesions?

Answer 12

Probiotics: live microorganisms which when administered in adequate amounts confer a health benefit on the host

Question 13

What are probiotics?

Answer 13

Probiotics: live microorganisms which when administered in adequate amounts confer a health benefit on the host.

Question 14

What are prebiotics?

Answer 14

Dietary fibers which promote health of benefitial bacteria.

Question 15

What is the effectiveness of arginine like on dental caries?

Answer 15

Arginine has been found to work well in conjunction with fluoride to prevent early coronal caries

Question 16

How effective have probiotics been found to be in prevention of dental caries?

Answer 16

Not very effective.

Question 17

What bacteria are plaque overlying carious lesions rich in?

Answer 17

Plaque overlying carious lesions found to have higher proportions of bacteria such as strep mutans, bifidobacteria and lactobacilli.

Question 18

How is proportion of strep mutans different in plaque compared to clinically healthy sites?

Answer 18

Proportion of strep mutans in plaque are often higher than clinically healthy sites.

Initial demineralization of the enamel could be induced by early colonizers alone but also oral environment can be modified by strep oralis.

Question 19

What are biofilms composed of?

Answer 19

Microbial cells encased within a matrix of extracellular polymeric substances such as polysaccharides, proteins, and nucleic acids.

Salivary components such as glycoproteins

Water channels are commonly found in biofilms

Steep O2 and pH gradients

Question 20

What do extracellular polysaccharides do in biofilms?

Answer 20

Promote bacterial adherence to the tooth surface

Contribute to the structural integrity of dentinal biofilms

Increase the porosity of biofilm

Create low pH values due to microbial catabolism

Question 21

What do intracellular polysaccharides do in biofilms?

Answer 21

Endogenous source of carbohydrates

Can be metabolized to produce acids during periods of nutrient limitation

Question 22

What is the pellicle composed of?

Answer 22

Peptides, proteins, and glycoproteins

Detected on clean enamel within 1 minute

Can reach equilibrium within 2 hours

Question 23

How do early colonizers meet the pellicle and what happens when they do?

Answer 23

They attach to the pellicle in approximately 3 minutes

Adhesin molecules determine whether the cell remains associated with the surface

Streptococcus and other obligate aerobes are these early colonizers

Question 24

What are the steps of biofilm formation?

Answer 24

1. Pellicle formation
2. Early colonizer aggregation
3. Coaggregation, coadhesion

Question 25

What is coaggregation and coadhesion?

Answer 25

Colonizing bacteria provide new receptors for attachment by other bacteria.

Biofilm infrastructure changes

Endogenous source of carbohydrates prolong acid production and lower plaque pH

Streptococci coaggregate intragenerically

Question 26

What are the benefits of the normal oral microbiota?

Answer 26

Colonisation resistance

Downregulating host inflammatory response

Aiding normal development of mouth physiology

Host defence

Question 27

What happens to the microbiota for it to become pathogenic?

Answer 27

Shifts from symbiotic relationships to dysbiosis responsible for initiating carious processes

Ecological shift may facilitate acid production

Question 28

What effect does plaque-induced disease have on the gums?

Answer 28

Gingivitis and periodontitis result from the host response to subgingival plaque biofilm

Question 29

What are the hypotheses for plaque formation?

Answer 29

Chemo-parastic theory (dental caries caused by acids from bacteria metabolising dietary carbohydrates)

Specific plaque hypothesis (Rat and human studies show transmission of mutans streptococci)

Non-specific plaque hypothesis (In the absence of streptococcus mutans, other acidoduric and acidogenic bacteria can initiate caries initiation)

Ecological plaque hypothesis (Changes in environment disrupt the homeostasis of dental plaque, range of acidogenic and aciduric species favoured)

Keystone pathogen hypothesis (Low-abundance microbial pathogens can orchestrate inflammatory disease by remodelling a normally benign microbiota into a dysbiotic one)

Question 30

Which bacteria is thought to be a keystone pathogen in periodontal microbiota?

Answer 30

Porphyromonas gingivalis

Question 31

When does early microbial colonization of the oral cavity take place?

Answer 31

Microbial exposure starts in-utero as microbes can cross the placenta. Pioneer groups lead to permanent colonisation within the first 24 hours of life.

Question 32

What evidence is there for vertical transmission of mutans streptococci occur?

Answer 32

Early colonisation of mutans streptococci in infants is indicative of a vertical transmission pattern.

20 - 25 % of infants aged 12 - 19 months are colonised with mutans streptococci.

Between 30 to 60% of mutans streptococci strains isolated from saliva of mothers and their babies exhibit similar or identical profiles.

Question 33

How does horizontal transmission of mutans streptococci take place?

Answer 33

Horizontal transmission of mutans streptococci can occur between siblings and colleagues.

Nursery school children contained identical genotypes of mutans streptococci strains in a study conducted by Mattos-Graner in 2001

Similarity between the mutans strains between family members eg fathers, siblings

Question 34

What bacteria colonize teeth before their eruption?

Answer 34

Streptococcus mutans and lactobacilli were thought to colonise the infant oral cavity during a window of infectivity of 19-31 months.

Limited ability to adhere to epithelial surfaces therefore requiring a non-shedding oral surface for persistent oral colonisation.

50 - 60% of pre-dentate 6 month old infants harboured streptococcus mutans.

Mutans streptococci found in both plaque samples and tongue furrow scraping samples.

A rich bacterial community exists in the infant oral cavity prior to tooth eruption.

Question 35

How is infant microbiome prior to tooth eruption different to their parents?

Answer 35

Around 5 months of age, infants show different microbiota, they have fewer microorganisms but they also have a greater microbial diversity. Increased presence of streptococcus mutans or lactobacilli may be predictive of streptococcus mutans or lactobacillus may be predictive of caries in dentate years but no conclusive evidence.

Question 36

How are primary enamel carious lesions different in composition to normal healthy sites?

Answer 36

Proportion of strep mutans found in plaque associated with enamel lesions are often higher than in clinically healthy sites.

Initial demineralisation of the enamel could be induced by early colonizers alone.

Streptococcus oralis can modify the environment to favour succession of aciduric species.

Question 37

Which bacteria were noted to correlate with deep carious lesions?

Answer 37

Bifidobacterium and streptococcus mutans

Plaque overlying carious lesions has also been found to have higher proportions of bacteria such as streptococcus mutans, bifidobacteria, and lactobacilli

Question 38

How does lactobacillus affect primary dentine carious lesions?

Answer 38

Lactobacilli could potentially have a suppressive effect on cariogenic streptococci but lactobacillus species have also been implicated as secondary pathogens in deep carious lesions.

Question 39

What are the major aetiological agents of early childhood caries?

Answer 39

Streptococcus mutans have been frequently isolated in plaque and saliva.

Question 40

What virulence factors do strep mutans have?

Answer 40

Insoluble glucan formation

Excessive acid production in response to a sucrose-containing diet

Question 41

What causes the shift in microbiome between primary and permanent teeth?

Answer 41

Hormonal changes during puberty affect the oral environment with increasing gram negative anaerobes

Adolescents may also have prostheses or oral appliances that change microbiome

Higher consumption of fermentable carbohydrates is also associated with a reduction in bacterial diversity.

Question 42

Which bacteria are present in high levels in permanent enamel carious lesions?

Answer 42

Streptococcus parasanguinis

Streptococcus salivarius

Streptococcus mutans in initial white spot lesion but no lactobacilli.

Question 43

Where does streptococcus mutans seem to have a more dominant role in dentine caries?

Answer 43

In dentine caries of primary teeth more than permanent teeth.