bacterial etiology of caries
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what are the sequence of events in plaque formation?
- 1-pellicle formation on the enamel surface of a new tooth pellicle-an organic film, proper toothbrushing removes reforms in minutes,
- predominantly protein of salivary origin
- 2-Initial colonization of bacteria, predominantly coccal in form yet only about 2% of Streptococcus are S. mutans
- 3-maturation and thickening of plaque
- -S. mutans and Lactobacillus sp. numbers increase -center of plaque becomes anoxic
- -sugar is fermented to lactic acid rather
- than oxidized to CO2 -acid
- produced results in demineralization of enamel
-process is reversible at early stages
in the venn diagram, describe the host and teeth portion.
- host immune response
- host saliva production
- irregular structures of teeth
Explain lactate acid role in producing caries.
- bacteria + sugar = acid = caries
- anoxic environment of bacterial biofilms increases lactate production
- lactate - fermentation product (no oxygen)
- lactic acid = most important but acetic acid is also produced
What is Miller's theory?
- Chemo-parasitic theory: proposes carbohydrates from food fermented by bacteria and resulting acids cause demineralization of enamel
- describes oral streptococci as "caries fungus"
- determines lactic acid is damaging metabolic acid
Describe the Stephan Curve.
- records pH of enamel minutes after glucos rinse - strongly supports Miller's chem-parasitic hypothesis
- pH of 5.5 is critical
- demineraliztaion of enamel occurs at/below 5.5
What is acid?
- acidic soln have many protons
- acids donate protons
- pH = -log [H+]
How does buffers affect pH?
- Buffers prevent the changes in pH
- 1. bicarbonate - most important buffer for saliva
- H+ +HCO3- <-> H2CO3 <-> CO2 + H2O
- 2. phosphate buffer system of saliva also contributes (not as much as bicarbonate)
- H+ + Na2HPO4 <-> NaH2PO4 + Na+
- 3. proteins of saliva also function as buffers
repeated sugar exposure increases acid production and enamel demineralization.
finding by Stephan
acid _____ demineralzation of hydroxyapatite.
- hydroxyapatite-calcium phosphate crystal in enamel
- Ca10 (PO4)6 (OH2)
acids protonate _______ in center of crystal.
- hydroxyl groups
- H+ removes negative charge required to coordinate positively charged calcium ions
patients that cannot metabolize fructose found to have 90% reduction in caries. Populations w/o sucrose in diet leads to what?
much lower incidences of caries
why is sucrose the most cariogenic of dietary sugars?
It releases more than 2x the energy of others.
Explain the 3 stages of the biofilm life cycle.
- 1. attachment: free-floating (planktonic) find a place and w/in minutes become attached. They begin to produce slimy extracellular polymeric substances (EPS) and to colonize the surface.
- 2) EPS production allows the emerging biofilm
- community to develop a complex, three-dimensional structure that is influenced
- by a variety of environmental factors. Biofilm communities can develop within hours.
- 3) Biofilms can propagate through detachment of
- small or large clumps of cells, or by a type of "seeding dispersal" that releases individual cells. Either type of detachment allows bacteria to
- attach to a surface or to a biofilm downstream of the original community.
some bacteria utilize ______ produced by S. mutans and lactobacillus as a nutrient source.
some bacteria can produce vitamin ___, a growth requirement for other bacteria
aerobic bacteria can consume oxygen and produce ROS that are especially toxic to _________.
in the first 0-4 hours, which microbial flora exist on the enamel pellicle?
- predominantly streptococci such as S. sanguis and S. oralis (only 2% of initial streptococci are mutans)
- some gram negatives Actinomyces
after initial adherence, plaque grows due to what?
- bacterial growth and cell division
- adherence of other bacteria
Glucans produced by initial adherent bacteria improve binding of S. mutans at later time in growth of plaque.
plaque becomes more acidic/basic as it thickens?
what is the most frequently isolated species from oral cavity?
MS are neither a unique casuative agent for white spot lesions, nor a mian determinant of the acidogenicity of plaque. T or F
the pH-lowering capacity of plaque may be related to the proportion of the what?
low pH non MS
which species is important in root surface caries?
characteristic of Actionomyces are....
- gram +
- aerotolerant anerobe
what 2 species are important in dentinal caries?
Lactobacillus and Actionomyces
what is the action of lysozyme-saliva enzyme?
- it hydrolyzes peptidoglycan
- enzyme is in saliva, tears, mucus
- it cleaves beta 1,4 glycosidic linkages of peptidoglycan
- a glycosidase, not a protease
what does IgA do?
- agglutinates bacteria
- prevents adherence
- has secretory associated protein which facilitates transport of IgA into saliva and appears to prolong stability
gingival sulcular fluid also secretes immunological components. Possible mechanism for host protection
- specific agglutinins
- inhibit colonization
- bind to and interfere with glycosyltransferases
- increase opsonization
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