Effect of Multiple Fluoride Applications on the Surface of Synthetic Hydroxypatite

Abstract

We investigated the effects of multiple fluoride applications on the surface structure of synthetic hydroxyapatite (HAp) using X-ray photoelectron spectroscopy (ESCA). Sodium fluoride (NaF, pH7.0) and acidulated phosphate fluoride (APF, pH3.6) were prepared to concentrations of 100, 1,000 and 9,000ppm fluoride. HAp was treated for four minuxes in each NaF and APF solution, washed and dried. The HAp samples were retreated three times at one hour intervals in the same way. Untreated HAp and calicum fluoride (CaF₂) were employed as controls. ESCA analysis was conducted with wide and narrow scanning, and the relative concentration investigated for the surface and the fourth layer (10.5nm) of the fluoride treated HAp.
F_1s2 and Ca_2p binding energy showed that the type of uptake fluoride was different between the surface and fourth layer depending on the pH, concentration, and application time. For the 9,000ppm F APF-HAp, CaF₂ was produced on the surface and in the fourth layer for all fluoride applications. For the 100 and 1,000ppm F APF-HAp, only FHAp formed on the surface, even as the level of fluoride in the applications increased. However, CaF₂ was seen in the fourth layer after four fluoride applications. On the other hand, when NaF was applied, FHAp formed on the surface for all fluoride applications and CaF₂ formed in the fourth layer at the second and fourth applications. The relative concentration of fluoride in the HAp indicated that fluoride uptake increased with increasing fluoride concentration in the application media, and wi h an increase in the number of applications. Multiple fluoride applications of low fluoride concentration produced CaF₂ in the deeper layers of HAp.