Factors controlling calcification in vitro: Fluoride and magnesium

Abstract

Fluoride has been reported to cause both inhibition and enhancement of calcification in vitro. However, those experiments all employed nonphysiological concentrations of at least one of the important ions, and in addition differed too much in experimental design to make it possible to evaluate the variables properly. In this study it was possible to obtain crystal formation with physiological concentrations of calcium, phosphate, fluoride, and magnesium at pH 7.4 and 37 °C by means of nucleators and to note both enhancement and inhibition of crystal formation so that the important variables could be identified. The product of the calcium and phosphate concentrations was the single most important variable; with products just below those found in adult humans there was enhancement by fluoride while with higher products there was inhibition. Contrary to previous reports, magnesium was not required in order to show inhibition. It was also shown for the first time that the concentrations of fluoride normally found in serum can enhance calcification in the presence of physiological concentrations of magnesium if the product of the calcium and phosphate concentrations is lower than normal. These findings suggest that normal serum concentrations of fluoride can act as a governor on the rate of calcification with fluctuations in the serum phosphate concentration, enhancing when the phosphate is low and inhibiting when it is high. Higher fluoride concentrations show more enhancement and less inhibition.