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MICROBIOLOGY OF DENTAL CARIES

MICROBIOLOGY OF DENTAL CARIES. Caries: Localized destruction of the tissues of the tooth by bacterial fermentation of dietary carbohydrates A multifactorial, plaque-related chronic infection of the enamel, cementum or dentine. Traces of plaque and decaying enamel. Enamel

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MICROBIOLOGY OF DENTAL CARIES

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  1. MICROBIOLOGY OF DENTAL CARIES Caries: Localized destruction of the tissues of the tooth by bacterial fermentation of dietary carbohydrates A multifactorial, plaque-related chronic infection of the enamel, cementum or dentine

  2. Traces of plaque and decaying enamel

  3. Enamel penetrated by bacteria

  4. Early enamel caries seen by polarized light microscopy

  5. MICROBIOLOGY OF DENTAL CARIES • Key factors in the development of caries: • Host • Susceptible tooth surface • Saliva • Plaque bacteria • Diet • Fermentable carbohydrates

  6. Interplay of major etiologic factors in dental caries

  7. MICROBIOLOGY OF DENTAL CARIES • Specific plaque hypothesis: • mutans streptococci are important in caries • initiation • Non-specific plaque hypothesis: • Heterogeneous groups of bacteria are involved • in caries initiation

  8. MICROBIOLOGY OF DENTAL CARIES Ecological plaque hypothesis: Cariogenic flora found in natural plaque are weakly competitive and comprise only a minority of the total community Increase in fermentable carbohydrates results in prolonged low pH, promoting the growth of acid- tolerant bacteria and initiating demineralization

  9. MICROBIOLOGY OF DENTAL CARIES Ecological plaque hypothesis: The balance in the plaque community turns in favor of mutans streptococci and lactobacilli There is a dynamic relationship between the bacteria and the host, and changes in major host factors such as salivary flow can affect plaque development

  10. Ecological plaque hypothesis

  11. MICROBIOLOGY OF DENTAL CARIES • Properties of cariogenic flora that correlate with • their pathogenicity: • Ability to rapidly metabolize sugars to acids • (acidogenicity) • Survival and growth under low pH conditions • (aciduricity) • Ability to synthesize extracellular and intracellular • polysaccharides

  12. glucosyltransferase (Glucan)n + n-fructose n-sucrose

  13. fructosyltransferase (Fructan)n + n-glucose n-sucrose

  14. “Primary enemy of the teeth” Lennart Nilsson The Body Victorious Streptococcus mutans

  15. CARIOGENICITY OF STREPTOCCUS MUTANS • Significant correlation between S. mutans counts in • saliva & plaque with the prevalence and incidence • of caries • Prevalence: The number of cases of a disease present • in a specified population at a given time • Incidence: The frequency of occurrence of any • disease over a period of time in relation to the • population in which it occurs • S. mutans can be isolated from precise sites on the • tooth surface before the development of caries

  16. CARIOGENICITY OF STREPTOCCUS MUTANS • Correlation between the progression of carious • lesions and S. mutans counts • Produces extracellular polysaccharides from sucrose • which facilitates microbial colonization • Most effective Streptococcus in experimental caries • in animals (rodents & non-human primates) • Ability to initiate and maintain growth and continue • acid production in sites with a low pH

  17. Glucose-6-phosphate Fructose-1,6-diphosphate Phosphoenolpyruvate Glyceraldehyde -3-phosphate Formation of end products of metabolism by mutans streptococci

  18. CARIOGENICITY OF LACTOBACILLUS SPECIES • Present in increased numbers in most carious • cavities 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)

  19. CARIOGENICITY OF LACTOBACILLUS SPECIES • Produce lactic acid in conditions below pH 5 • (acidogenic) • However: • Affinity for the tooth surface is low • Numbers in dental plaque in early carious lesions • are usually low • Their population size is a poor predictor of the • number of future plaques • Their numbers in saliva increase only after • caries develop

  20. CARIOGENICITY OF LACTOBACILLUS SPECIES • Present consensus: • Lactobacilli are not involved in the initiation of • dental caries • They are involved in the progression of the • lesion deep into enamel and dentine • They are pioneer organisms in the advancing • carious process

  21. DEMINERALIZATION • Low pH causes demineralization by reducing • the concentration of the tribasic phosphate (PO43-) • which is needed to form hydroxyapatite • 10Ca2+ + 6PO43- + 2H2O ---> 2H+ + Ca10 (PO4)6(OH)2 • hydroxyapatite

  22. DEMINERALIZATION Low pH tends to reduce the concentration of tribasic phosphate by adding H+ to phosphate 6PO43- + H+ ----------> 6HPO42- + H+ ----------> 6H2PO41- pK= 7.0 pK= 4.0

  23. MICROBIOLOGY OF DENTAL CARIES • Strategies to control or prevent caries: • • Sugar substitutes • • Fluoridation (to increase enamel hardness) • • Fissure sealants • • Control of cariogenic flora • Antimicrobials • Passive immunization? • Replacement therapy? • Vaccines??

  24. Fluoride ions Substitute for the hydroxyl groups in hydroxyapatite (Fluoroapatite less soluble in acid) Promote remineralization of early carious lesions

  25. 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

  26. MICROBIOLOGY OF DENTAL CARIES Strategies to control or prevent caries: Passive immunization Antibodies against antigen I/II of mutans streptococci inhibit recolonization after chlorhexidine treatment Monoclonal antibodies produced in transgenic plants prevented recolonization for 4 months

  27. MICROBIOLOGY OF DENTAL CARIES Strategies to control or prevent caries: Sugar substitutes Xylitol inhibits sugar metabolism of mutans streptococci as well as glycolysis pH is maintained at 7, vs reduction to 5 by sucrose

  28. MICROBIOLOGY OF DENTAL CARIES • Strategies to control or prevent caries: • Replacement therapy • Low virulence mutants of mutans streptococci deficient in GTF or lactate dehydrogenase activity • More competitive S. salivarius that can displace S. mutans

  29. MICROBIOLOGY OF DENTAL CARIES • Strategies to control or prevent caries: • Antimicrobials • Chlorhexidine • Inhibits sugar transport in streptococci • Inhibits amino acid uptake and catabolism in S. sanguis • Inhibits a protease of P. gingivalis • Affects membrane functions, such as ATP synthase and maintenance of ion gradients in streptococci

  30. MICROBIOLOGY OF DENTAL CARIES • Strategies to control or prevent caries: • Antimicrobials • Triclosan • Inhibits acid production by streptococci • Inhibits a protease of P. gingivalis • Enhanced by co-polymer or zinc citrate • “Substantive” : binds effectively to oral surfaces, like chlorhexidine

  31. MICROBIOLOGY OF DENTAL CARIES Microbiological tests: To identify caries risk factors in patients with extensive or recurrent caries, prior to delivering dental care (e.g. extensive crown and bridge treatment) High salivary counts of mutans streptococci (> 106/mL) and lactobacilli (> 104/mL) indicate high risk of disease

  32. Culture slide test to detect mutans streptococci in saliva

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