Using a new technique, the diffusion coefficient, D, of NaF in plaque at 37 °C was measured by monitoring its clearance from a thin layer of plaque. D, for both the sodium and the fluoride ions, was 4.2 × 10-6cm2s-t1, which is about one quarter of the diffusion coefficient of NaF in water at 37 °C. No significant change in D was found over the physiological pH range of plaque. It is concluded that fluoride diffuses rapidly in plaque, with a halving-time T1 2, of 6.7s for a 100 μm layer of plaque. This suggests that a thorough cleaning and polishing of the teeth may not be essential before topical application of fluoride. © 1980.
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