An intra-oral appliance study of the plaque microflora associated with early enamel demineralization

An intra-oral appliance model was used to investigate the composition of the plaque microflora associated with early enamel demineralization. Enamel sections, with exposed windows, were mounted on lower removable appliances, and the devices were worn by volunteers for three-week periods under three experimental conditions. These were: (1) "normal" plaque conditions, (2) extra-oral sucrose applications nine times daily, and (3) inoculation of each volunteer's own mutans streptococci onto the test sites and sucrose applications as described for (2). After 21 days, the plaque overlying each window was removed, and the bacterial composition was determined. Changes in mineral content of the associated enamel were measured by microradiography and microdensitometry, and the total mineral loss (delta z) that had occurred at each site was calculated. The 144 sites studied were divided into four demineralization groups by delta z value, with an increase in mineral loss from group 1 to group 4. A progressive and significant increase in the isolation frequency of mutans streptococci occurred from delta z group 1 to group 4 sites. These organisms were isolated from the plaque of every location with enamel mineral loss of over 1000 delta z units, but were not detected in 27% of the group 3 sites. Lactobacilli comprised 2% to 3% of the total cultivable microflora in groups 1-3 sites, but were found in significantly higher proportions (18%) at those enamel sites experiencing the most extensive mineral loss (group 4). No significant relationship was found between demineralization and the levels of Actinomyces species or Veillonella