Microbiology of Caries.ppt
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Transcript of Microbiology of Caries.ppt
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MICROBIOLOGY OF DENTAL CARIESCaries:
Localized destruction of the tissues of thetooth by bacterial fermentation of dietarycarbohydrates
A multifactorial, plaque-related chronicinfection of the enamel, cementum or dentine
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Traces of plaque
and
decaying enamel
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Enamelpenetrated by bacteria
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Early enamelcaries seen by polarized light microscopy
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MICROBIOLOGY OF DENTAL CARIESKey factors in the development of caries:
HostSusceptible tooth surfaceSaliva
Plaque bacteria
DietFermentable carbohydrates
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Interplay of major etiologic factors in dental caries
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MICROBIOLOGY OF DENTAL CARIESSpecific plaque hypothesis:
mutans streptococci are important in cariesinitiation
Non-specific plaque hypothesis:
Heterogeneous groups of bacteria are involvedin caries initiation
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MICROBIOLOGY OF DENTAL CARIESEcological plaque hypothesis:
Cariogenic flora found in natural plaque are weaklycompetitive and comprise only a minority of thetotal community
Increase in fermentable carbohydrates results inprolonged low pH, promoting the growth of acid-tolerant bacteria and initiating demineralization
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MICROBIOLOGY OF DENTAL CARIESEcological plaque hypothesis:
The balance in the plaque community turns in favorof mutans streptococci and lactobacilli
There is a dynamic relationship between the bacteriaand the host, and changes in major host factors suchas salivary flow can affect plaque development
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Ecological plaque hypothesis
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MICROBIOLOGY OF DENTAL CARIESProperties of cariogenic flora that correlate withtheir pathogenicity:
Ability to rapidly metabolize sugars to acids(acidogenicity)
Survival and growth under low pH conditions(aciduricity)
Ability to synthesize extracellular and intracellularpolysaccharides
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n-sucrose glucosyltransferase(Glucan) n + n-fructose
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n-sucrose fructosyltransferase(Fructan) n + n-glucose
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Primary enemy of the teeth Lennart NilssonThe Body Victorious
Streptococcus mutans
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CARIOGENICITY OF STREPTOCCUS MUTANSSignificant correlation between S. mutans counts insaliva & plaque with the prevalence and incidenceof cariesPrevalence: The number of cases of a disease presentin a specified population at a given timeIncidence: The frequency of occurrence of anydisease over a period of time in relation to thepopulation in which it occurs
S. mutans can be isolated from precise sites on thetooth surface before the development of caries
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CARIOGENICITY OF STREPTOCCUS MUTANSCorrelation between the progression of cariouslesions and S. mutans counts
Produces extracellular polysaccharides from sucrosewhich facilitates microbial colonization
Most effective Streptococcus in experimental cariesin animals (rodents & non-human primates)
Ability to initiate and maintain growth and continueacid production in sites with a low pH
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Formation of end products of metabolism bymutans streptococciGlucose-6-phosphate Fructose-1,6-diphosphate Phosphoenolpyruvate Glyceraldehyde-3-phosphate
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CARIOGENICITY OF LACTOBACILLUS SPECIESPresent in increased numbers in most cariouscavities affecting enamel & root surfaces
Numbers in saliva correlate with caries activity
Some strains produce caries in gnotobiotic rats
Initiate and maintain growth at low pH (aciduric)
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CARIOGENICITY OF LACTOBACILLUS SPECIESProduce lactic acid in conditions below pH 5(acidogenic)
However:Affinity for the tooth surface is lowNumbers in dental plaque in early carious lesionsare usually lowTheir population size is a poor predictor of thenumber of future plaquesTheir numbers in saliva increase only aftercaries develop
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CARIOGENICITY OF LACTOBACILLUS SPECIESPresent consensus:
Lactobacilli are not involved in the initiation ofdental caries
They are involved in the progression of thelesion deep into enamel and dentine
They are pioneer organisms in the advancingcarious process
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DEMINERALIZATIONLow pH causes demineralization by reducingthe concentration of the tribasic phosphate (PO43-)which is needed to form hydroxyapatite
10Ca2+ + 6PO43- + 2H2O ---> 2H+ + Ca10 (PO4)6(OH)2 hydroxyapatite
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DEMINERALIZATIONLow pH tends to reduce the concentration oftribasic phosphate by adding H+ to phosphate
6PO43- + H+ ----------> 6HPO42- + H+ ----------> 6H2PO41- pK= 7.0 pK= 4.0
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MICROBIOLOGY OF DENTAL CARIESStrategies to control or prevent caries:
Sugar substitutes Fluoridation (to increase enamel hardness) Fissure sealants Control of cariogenic floraAntimicrobials Passive immunization?Replacement therapy?Vaccines??
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Fluoride ions
Substitute for the hydroxyl groups in hydroxyapatite (Fluoroapatite less soluble in acid)
Promote remineralization of early carious lesions
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Fluoride ions
Interfere with bacterial membrane ion permeability
Reduce glycolysis(inhibition of enolase: phosphoglycerate -> phosphoenolpyruvate)
Inactivate key metabolic enzymes by acidifying bacterial cell interior
Inhibit synthesis of polysaccharides
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MICROBIOLOGY OF DENTAL CARIESStrategies to control or prevent caries:
Passive immunizationAntibodies against antigen I/II of mutans streptococci inhibit recolonization after chlorhexidine treatment
Monoclonal antibodies produced in transgenic plants prevented recolonization for 4 months
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MICROBIOLOGY OF DENTAL CARIESStrategies to control or prevent caries:
Sugar substitutesXylitol inhibits sugar metabolism of mutans streptococci as well as glycolysispH is maintained at 7, vs reduction to 5 by sucrose
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MICROBIOLOGY OF DENTAL CARIESStrategies to control or prevent caries:
Replacement therapyLow virulence mutants of mutans streptococci deficient in GTF or lactate dehydrogenase activityMore competitive S. salivarius that can displace S. mutans
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MICROBIOLOGY OF DENTAL CARIESStrategies to control or prevent caries:
Antimicrobials ChlorhexidineInhibits sugar transport in streptococciInhibits amino acid uptake and catabolism in S. sanguisInhibits a protease of P. gingivalisAffects membrane functions, such as ATP synthase and maintenance of ion gradients in streptococci
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MICROBIOLOGY OF DENTAL CARIESStrategies to control or prevent caries:
Antimicrobials TriclosanInhibits acid production by streptococciInhibits a protease of P. gingivalisEnhanced by co-polymer or zinc citrateSubstantive : binds effectively to oral surfaces, like chlorhexidine
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MICROBIOLOGY OF DENTAL CARIESMicrobiological tests:
To identify caries risk factors in patients withextensive or recurrent caries, prior to deliveringdental care (e.g. extensive crown and bridgetreatment)
High salivary counts of mutans streptococci(> 106/mL) and lactobacilli (> 104/mL) indicatehigh risk of disease
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Culture slide test to detect mutans streptococci in saliva
Flourappatite is much less likely to be degradedKnow the general mechanism for this.