The purpose of this study was to investigate the contribution of fluoride and titanium uptake in powdered enamel to the acquisition of acid resistance.
Experiments were made in vitro by treatment with solution of (NH4) 2 TiF6 (9000 ppm of F, pH 3.4) or APF (acidulated phosphate fluoride solution) for 3 minutes at 37°C with powdered enamel (particle size 70-140 μm), and 24-hour washing with synthetic saliva or 1M KOH solution was used to distinguish the soluble and permanently bound fluoride. Chemical analyses were performed to determine fluoride, titanium, calcium, and phosphorus. Acid solubility of enamel was evaluated to determine the calcium released from powdered enamel into acetate buffer (pH 4.5). The reaction products were identified by X-ray diffractometry.
A large amount of fluoride uptake, most of it in the form of CaF2, was found after application of APF. Synthetic saliva or KOH washing removed most of the fluoride from APF treated enamel, but (NH4) 2 TiF 6-treated enamel had lower levels of fluoride uptake and higher retention after both washings. These facts indicated that a higher level of more permanently bound fluoride formed in (NH4) 2 TiF6-treated enamel.
Titanium in (NH4) 2 TiF6-treated enamel was resistant to synthetic saliva washing, but the KOH wash caused a partial release of titanium.
The acid solubility test of fluoride-treated enamel showed the same degree of acid resistance before and after synthetic saliva wash. However, the KOH wash decreased an acid resistance of both types of fluoride-treated enamel. A decrease of acid resistance in APF-treated enamel may contribute to the release of alkali-soluble fluoride such as CaF2. In the case of (NH4) 2 TiF6, a decrease of acid resistance might be related to the titanium concentration in enamel. The release of fluoride and titanium from (NH4) 2 TiF6-treated enamel into 1MKOH solution suggests a hydrolysis of titaniumfluoride compound, which forms an organometallic bond with the enamel protein called“glaze”, rather than a release of CaF2.
As the results, it is suggested that glaze-like substance is soluble in strong alkali such as 1MKOH soluion but stable in acid circumstances, and controls acquisition of acid resistance of powdered enamel.