Plaque microcosm mineralization and fluoride: pH response and mineral deposition

Objectives: To study the effect of high fluoride concentrations and casein on mineral deposition and pH responses in microcosm dental plaque biofilms with and without exposure to a pH 5.0 calcium-phosphate-monofluorophosphate-urea mineralising solution (CPMU). Methods: Ten microcosm biofilms were grown on prepared enamel blocks for 28 days in a ‘Multiplaque Artificial Mouth' culture system with continuously-supplied artificial saliva (DMM), pulsed with five 6-min applications of 10% sucrose (1.5 ml) over 12 hours followed by 12 hours recovery without sucrose. The five pairs of plaques were supplied 0, 1000, 3000 and 5000 ppm fluoride or 2% casein twice-daily, with one of each pair supplied CPMU twice-daily (1.5ml/6min). Plaque pH responses and Ca, phosphate and fluoride were measured. Results: In the absence of fluoride, the sucrose applications reduced the pHsuc(min) to 3.7-3.9 with a pHsuc(max) of 4.6. During the 12-hour recovery the pH(max) reached 6.0. CPMU pulsing increased the recovery pH(max) by approx 0.7 pH unit. Fluoride increased the pHsuc(min) to approx 4.4 and the pHsuc(max) to 4.9-5.8 but decreased the recovery pH(max). In the absence of fluoride, plaque mineral levels were the same with and without exposure to CPMU, application of casein having no effect. Fluoride concentrations of 0, 1000, 3000 and 5000 ppm, in the absence of CPMU, yielded Ca levels of 0.22 (0.06), 0.17 (0.02), 0.75 (0.05), and 1.50 (0.06) mmol/g protein (SE, n=4) respectively. At all fluoride concentrations, Ca deposition due to exposure to CPMU was 2.64 mmol/g protein. Phosphate and fluoride deposition patterns were similar to Ca. Conclusions: The sucrose application regime yielded extremely acidic cariogenic plaques. In the absence of fluoride, mineral levels did not increase despite the application of CPMU. Fluoride in the 1000 ppm+ range with and without CPMU increased mineral deposition and reduced the magnitude of the plaque pH responses.