Structure and acid resistance of fluoride-treated hydroxyapatite particles

Topical fluoride is used in clinical dentistry to prevent dental caries.The primary reaction product formed on the tooth surface after topical fluoride application is calcium fluoride (CaF 2 ).In this study, we investigated the effect of deposited CaF 2 on the acid resistance of fluoride-treated hydroxyapatite (HAp).Commercial HAp particles were treated with two types of fluoride-containing acetic acid-sodium acetate (Ac-AcNa) buffer solutions, with and without the addition of phosphate ions.X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) analyses confirmed the formation of fluorine-substituted hydroxyapatite (F-HAp), along with a hydration layer containing calcium phosphate and CaF 2 .Phase composition analysis revealed that the presence of phosphate ions in the fluoride treatment solution reduced the amount of CaF 2 deposited.Acid resistance evaluation and phase composition analysis indicated that the initial dissolution rate of the fluoride-treated HAp in Ac-AcNa buffer solutions decreased on surfaces densely covered with CaF 2 particles.