The effect of pH upon fluoride uptake in intact enamel

The relationship between pH and fluoride uptake in intact enamel of permanent premolars was investigated by using: (1) a sodium fluoride dentifrice, (2) a potassium fluoride + manganese chloride dentifrice, and (3) a sodium fluoride solution of the same fluoride concentration. The first part of this paper deals with the in vitro uptake of fluoride from dentifrice slurries and from sodium fluoride solutions of different pH ranging from 7.1 to 4.5. This investigation showed that there was no significant difference between the agents but that the effect of the pH was significant. The uptake of fluoride in the form of fluorapatite was more than five times larger at the lower pH level. The second part of the paper deals with the rate of fluoride uptake (increase in fluoride content) from dentifrices in the same pH range. It was shown that the three agents gave the same initial rate of fluoride uptake (about 50 parts/10(6)/min) at pH 6 and that the rate of fluoride uptake in the outer layer of the enamel was proportional to the hydrogen ion activity.