Analysis of tooth-bound fluoride after the application of coating materials on the enamel surface with an in-air micro PIXE/PIGE

Tooth-bound (KOH-insoluble) fluoride prevents caries via long retention within the tooth structure. Tooth-bound fluoride in the enamel was investigated after applying various fluoride-containing tooth-coating materials using an in-air micro [Formula: see text] PIXE/PIGE system. Three different fluoride-containing or a non-fluoride containing coating materials were applied to the coronal enamel surface of 24 extracted human molars. The samples were stored in water for 1 or 7 days and then sectioned into two slices. One slice was immersed in 1M KOH solution for 24 h for KOH-insoluble fluoride (KOH(T)) analysis. The second slice was not subjected to KOH treatment and was used to analyze the whole fluoride (KOH-soluble plus insoluble fluoride: KOH(U)). Fluorine and calcium distribution were measured in all the slices with [Formula: see text]PIXE/PIGE. KOH(U) was higher than KOH(T) on some materials, especially those that released more fluoride. For KOH(T), there was no significant difference among all fluoride-containing materials in the 7-day group. However, there were significant differences in the KOH(U) samples during the same period. PIXE/PIGE analysis confirmed the presence of tooth-bound fluoride in the enamel adjacent to the fluoride-containing coating materials. The amount of tooth-bound fluoride depended on the type of material.