Fixation of Topically Applied Fluoride in Enamel

It has recently been shown that a portion of the topically applied fluoride which deposits in intact surface enamel will leach away,12 and that the net increase in firmly fixed fluoride is considerably less than that suggested from in vitro experiments. According to Brudevold, McCann, Nilsson and Gron,' the loss of fluoride occurs mainly during the first 24 hours after the fluoride exposure, and represents unreacted fluoride and in part, CaF2. The purpose of the present investigation was to develop a method for increasing fixation of topically applied fluoride. Fluoridetreated intact enamel was first washed for different periods to find out if all the deposited fluoride could be washed away, and how long this would take. In subsequent experiments, which employed the most effective washing procedure, it was shown that there is a significant increase in bound fluoride as the interval between the fluoride exposure and the washing is increased. These findings suggested that a prolonged reaction time would result in greater fluoride fixation and led to a third series of experiments, in which the ability of different agents to seal fluoride-exposed enamel was assessed. It was thought that agents that would effectively block the enamel, thus prolonging the reaction time and increasing fixation of fluoride under the conditions of these experiments, might be subjected to further testing in vivo in future work.