Effect of calcium in model plaque on the anticaries activity of fluoride in vitro

The uptake of calcium by a polysaccharide (agarose) gel used as a model for plaque from a two-step treatment (consisting of a calcium rinse followed by a fluoride treatment) and the effect of the deposited calcium in model plaque on caries lesion formation in enamel were determined. Calcium uptake was measured by treatment of the model plaques with [45Ca]-CaCl2 solutions with or without NaF. A two-step treatment consisting of calcium followed by fluoride produced a 100% increase in calcium content of model plaque, presumably due to the formation of CaF2, compared with a treatment with artificial saliva followed by calcium alone. The effects of these increased plaque minerals on caries lesion formation were studied by subjecting model-plaque-covered enamel blocks to a cyclic demineralization-remineralization treatment. Artificial-plaque-covered enamel blocks were treated daily with 180 ppm calcium for ten min, then 100 ppm fluoride for ten min, followed by demineralization for 16 h, and finally, remineralization for seven h and 40 min. After five days, the blocks were sectioned, and lesion formation was determined by microradiography-microdensitometry. Artificial plaque treated with a calcium rinse followed by a fluoride rinse reduced lesion size by 90%, compared with a 68% reduction by a fluoride rinse alone. When the experiment was repeated with a simulated pre-brush calcium rinse (180 ppm calcium) followed by a fluoride dentifrice suspension (110 ppm fluoride), lesion size was reduced by 46%, compared with a 32% reduction by the fluoride dentifrice suspension alone.