Plaque microcosm mineralization and fluoride: effects on the microbial populations

Objectives: To investigate the climax microbiota of plaque microcosms pulsed with high fluoride with and without pulses of pH 5.0 calcium phosphate-monofluorophosphate urea (CPMU) mineralising solution. Methods: Ten microcosm biofilms were grown for 28 d on prepared enamel blocks in the ‘Multiplaque Artificial Mouth' and pulsed for 6 min (1.5 ml) with 10% sucrose 5 times in 12 h (3h intervals) followed by 12-h with no sucrose. Pairs of plaques were pulsed for 6min with 0, 1000, 3000 and 5000ppm fluoride or 2% w/v casein for 30 min (1.25 ml). CPMU was also pulsed to one of each pair twice daily for 6 min (1.5 ml). The microbiota was analyzed by Checkerboard DNA:DNA hybridization analysis of 40 species. Results: Despite the acidifying sucrose regime, urea metabolism following CPMU treatment resulted in no change in the final microbiota composition in these very large plaques. Increasing the concentration of fluoride resulted in small increases in Actinobacillus actinomycetumcomitans and Campylobacter rectus only. Pulsing with 2% casein yielded significant (p < 0.01) changes: a 4.2-fold increase in Streptococcus anginosus and approx. 50% decreases in Lactobacillus rhamnosus, Capnocytophaga gingivalis and Micromonas micros. Conclusion: Variation in mineral deposition into plaque sited on tooth enamel by CPMU applied twice daily had no effect on the microbiota after 4 weeks culture. Pulsing with high fluoride concentrations at toothpaste levels had minor effects, greater effects were produced by pulsing twice daily with 2% casein.