Assertion: fluoride's effect | /r/HasProperty | based on the concentration
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Source sentences:
text: Perhaps the great effect of fluoride to control caries is based on the concentration needed for it to exert its effect: when fluoride is present at concentrations as low as 1 µM (approximately 0.02 ppm F), the oral fluids (saliva, plaque fluid) are supersaturated with respect to the mineral phase fluorapatite.