Effect of amine fluoride solution with different fluoride concentrations and different pH on tooth bound fluoride

Introduction: The tooth-bound fluoride (F) effect on caries has not been clearly demonstrated. The enamel resistance to lesion formation increased with increasing tooth-bound F content, but not linearly to the concentration of fluoride especially when high fluoride concentration (professionally applied topical fluorides) is used. On the other hand it is important to avoid the possible excessive fluoride intake and the resultant fluorosis. The aim of this in vitro study was to study whether reducing the fluoride concentration of an amine fluoride solution from 1 to 0.25% F and its pH from 5.3-4.0 would affect the amounts of tooth-bound fluoride. Material and Methods: Surgically removed human third molars were used. The teeth were brushed with non-fluoride pumice powder and randomly divided into three main groups, with 10 teeth in each group. Each group of teeth was selected for treatment with three different amine fluoride concentrations (1, 0.5, and 0.25% F). Four enamel slabs were cut from buccal or lingual surfaces of each tooth. All surfaces of the slabs were covered with dental wax except for the enamel surface. One slab from each tooth was assigned at random to one of four subgroups in order to study effects of different pH. Each of the three subgroups of slabs was shaken for 3 min in an amine fluoride solution (1, 0.5, or 0.25% F) (Aminfluorid otopina, Belupo, Croatia) with pH 5.3, 4.5 and 4.0. These treatments were repeated on 3 successive days. One subgroup of slabs without treatment served as the control. After the treatment the alkali soluble fluoride were removed by KOH (Caslavska et al., 1975). Afterwards, the concentration of the tooth-bound fluoride was determined after acid etching using an ion-selective electrode. The calcium concentration in the etch solution was determined by atomic absorption spectrophotometery to check etching depth. The amounts of F and the surface areas of the slab were used to calculate the tooth-bound fluoride (ľg/cm 2). Results: The statistically significant increase in tooth bound fluoride up to 20 ľm was observed in all groups compared with control group (P 0.05) and was superior to 0.25% amine fluoride solution, regardless of acidity. The amounts of tooth-bound fluoride depended on concentration of fluoride and on the acidity of the solution. The highest amounts of fluoride were observed in enamel treated with the highest acidic solutions at any fluoride concentration (P<0.05). Conclusion: It could be concluded that lowering the standard fluoride concentration by half result in the similar fluoride uptake in the enamel. The use of highly acidic preparations could further increase fluoride content in enamel.