Differences in pH fall, phosphorus content and dissolution of enamel in layers of the oral bacterium Streptococcus mutans deposited in vitro on bovine enamel granules with and without fluoride varnish

Bovine enamel granules were treated with fluoride varnish for 24 h. Samples of F-treated and untreated control enamel were covered with maleic-acid-NaOH buffer (pH 5.8) previously saturated with enamel salts and containing a standard amount of fresh Strep, mutons cells plus KCl and MgCl₂ (6 and 1 mM, respectively). The cells were centrifuged on the enamel; sucrose was added to the test and to control systems with fluoridated and non-fluoridated enamel; distilled water was added to non-fermenting controls. After incubation at 37 °C for intervals up to 2 h, fluoridation of the enamel had reduced the drop in pH of Strep, mutans plaque by 0.7 pH unit and reduced the release of Ca and P from enamel. Bacterial P levels were also significantly reduced in plaque in contact with fluoridated enamel. Magnesium concentrations outside the enamel were not altered.