Microbiology of Dental Caries Flashcards
How many phylotypes colonize the oral cavity?
19000
What are the features of dental biofilms?
It is highly organized
Planktonic bacteria leave or join the biofilm
Also has archaea, yeasts, parasites, and viruses
What causes plaque-induced disease?
Shifts from symbiotic microbial relationships to dysbiosis responsible for initiating carious processes.
Ecological shift may facilitate acid production.
How are plaque biofilms associated with the gingiva?
Gingivitis and periodontitis result from the host response to subgingival plaque biofilm
What kind of interaction do streptococcus and candida have?
Streptococcus plaques and candida albicans can co-interact to increase the pathogenesis.
What microorganisms cause primary enamel carious lesions?
Non-mutans streptococci and actinomyces
Acid production by streptococcus mutans and streptococcus sabrinus is higher than that of other oral streptococci.
How much of the oral microbiota consists of strep mutans?
Strep mutans constitutes about 30% of the total microbiota and is less prevalent in progressing areas of dental caries.
How does candida affect dental caries?
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
What does strep mutans do in dental caries?
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.
What do lactobacilli do to dental caries?
Lactobacilli could potentially have a suppressive effect on cariogenic streptococci but lactobacillus species have also been implicated as secondary pathogens in deep carious lesions.
How are primary and secondary dentition different in terms of caries risk?
Healthy primary and permanent teeth harbour different supragingival microbial profiles in children.
What are probiotics and how effective where they for preventing carious lesions?
Probiotics: live microorganisms which when administered in adequate amounts confer a health benefit on the host
What are probiotics?
Probiotics: live microorganisms which when administered in adequate amounts confer a health benefit on the host.
What are prebiotics?
Dietary fibers which promote health of benefitial bacteria.
What is the effectiveness of arginine like on dental caries?
Arginine has been found to work well in conjunction with fluoride to prevent early coronal caries
How effective have probiotics been found to be in prevention of dental caries?
Not very effective.
What bacteria are plaque overlying carious lesions rich in?
Plaque overlying carious lesions found to have higher proportions of bacteria such as strep mutans, bifidobacteria and lactobacilli.
How is proportion of strep mutans different in plaque compared to clinically healthy sites?
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.
What are biofilms composed of?
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
What do extracellular polysaccharides do in biofilms?
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
What do intracellular polysaccharides do in biofilms?
Endogenous source of carbohydrates
Can be metabolized to produce acids during periods of nutrient limitation
What is the pellicle composed of?
Peptides, proteins, and glycoproteins
Detected on clean enamel within 1 minute
Can reach equilibrium within 2 hours
How do early colonizers meet the pellicle and what happens when they do?
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
What are the steps of biofilm formation?
- Pellicle formation
- Early colonizer aggregation
- Coaggregation, coadhesion
What is coaggregation and coadhesion?
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
What are the benefits of the normal oral microbiota?
Colonisation resistance
Downregulating host inflammatory response
Aiding normal development of mouth physiology
Host defence
What happens to the microbiota for it to become pathogenic?
Shifts from symbiotic relationships to dysbiosis responsible for initiating carious processes
Ecological shift may facilitate acid production
What effect does plaque-induced disease have on the gums?
Gingivitis and periodontitis result from the host response to subgingival plaque biofilm
What are the hypotheses for plaque formation?
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)
Which bacteria is thought to be a keystone pathogen in periodontal microbiota?
Porphyromonas gingivalis
When does early microbial colonization of the oral cavity take place?
Microbial exposure starts in-utero as microbes can cross the placenta. Pioneer groups lead to permanent colonisation within the first 24 hours of life.
What evidence is there for vertical transmission of mutans streptococci occur?
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.
How does horizontal transmission of mutans streptococci take place?
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
What bacteria colonize teeth before their eruption?
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.
How is infant microbiome prior to tooth eruption different to their parents?
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.
How are primary enamel carious lesions different in composition to normal healthy sites?
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.
Which bacteria were noted to correlate with deep carious lesions?
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
How does lactobacillus affect primary dentine carious lesions?
Lactobacilli could potentially have a suppressive effect on cariogenic streptococci but lactobacillus species have also been implicated as secondary pathogens in deep carious lesions.
What are the major aetiological agents of early childhood caries?
Streptococcus mutans have been frequently isolated in plaque and saliva.
What virulence factors do strep mutans have?
Insoluble glucan formation
Excessive acid production in response to a sucrose-containing diet
What causes the shift in microbiome between primary and permanent teeth?
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.
Which bacteria are present in high levels in permanent enamel carious lesions?
Streptococcus parasanguinis
Streptococcus salivarius
Streptococcus mutans in initial white spot lesion but no lactobacilli.
Where does streptococcus mutans seem to have a more dominant role in dentine caries?
In dentine caries of primary teeth more than permanent teeth.
