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Lesion Initiation

  • MS present in low numbers in plaque (carrier state)

  • Frequent sugar supply gives MS competitive advantage

  • ECP helps adhere them rmly to tooth surface

  • Metabolism of sugar to acid byproducts lowers pH

  • Few organisms can survive in low pH (aciduric)

  • MS proportions increase

  • This lowers the pH further and decreases the number of competing organisms

  • Once the pH low enough (critical pH, 5.0-5.5) tooth mineral begins dissolving

  • Mineral loss follows down the grain of the enamel rods

mineral lost from hydroxyapatite crystals

salivary buffers

fluoroapatite near tooth surface less soluble in acid

lowest pH at plaque-tooth interface

saliva remineralizes surface first

tiny hydrogen ion penetrates deeply

incipient caries lesions

visible as white spot

not visible on radiographs

cariogenic plaque

incipient caries lesion

high proportions of mutans streptococci

created by frequent or prolonged exposure to fermentable carbohydrates

MS concentrated at plaque tooth interface

ECPs maintain tight attachment & decrease permeability

intact surface layer

incremental growth lines striae of Retzius

X36

microradiograph of ground section of incipient lesion

incipient caries lesion at contact area

2

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