Alkali-soluble and insoluble fluoride in erupted and unerupted sound enamel of human third molars in vivo

Abstract

The amounts of firmly and loosely bound fluoride were determined in sound enamel of unerupted and erupted teeth which had been exposed in vivo for 1–16 yr to brushing at least once a day, and occasionally to mouth rinsing and the application of sealers. Enamel was sampled by an acid-etch procedure, and the fluoride levels were measured with an adapted fluoride ion-selective electrode. Unerupted enamel was etched significantly ( p < 0.05) deeper than erupted enamel up to a depth of at least 8 μm. Significant differences ( p < 0.05) were found between the mean enamel fluoride concentrations of unwashed and alkali-washed, erupted teeth up to a depth of at least 3 μm and also between unwashed or washed, erupted versus unwashed or washed, unerupted teeth. At a depth of 3 μm, the fluoride treatments of enamel had increased the total amount of fluoride by approx. 78% of which approx. 53% was loosely bound fluoride (like CaF 2) and 47% firmly bound (like fluoroapatite). No increase in sound enamel fluoride as a result of topical treatments over a period of up to 16 yr could be found at a level deeper than 20 μm.