Chemical Composition of the Surfacc of F-treated Dental Enamel

Abstract

This study was conducted using X-ray photoelectron spectroscopy (ESCA) with an argon ion etching system to determine the chemical composition of the surface of dental enamel after fluoride treatment. The enamel surface was treated for four minutes with sodium fluoride (NaF) or acidulated phosphate fluoride (APF) which was adjusted to a fluoride concentration to 9,000 ppm. F-treated enamels were measured in a depth profile (surface to 0.3 μm depth) with wide scanning for qualitative analysis and narrow scannings for quantitative analysis of calcium (Ca), phosphorus (P), oxygen (O), fluoride (F), carbon (C) and nitrogen (N) for quantitative analysis. ESCA analysis showed that Ca, P, C and O were present from the surface to 11th layer (0.3 μm) of the untreated enamel, however, N was only in the surface and 2nd layers. The Ca/P ratio for each layer of untreated enamel (1.44) was lower than the stoichiometric value (1.67) of hydroxyapatite. It is suggested that the subsurface pellicle forms from the surface to 60 nm depth. When enamel was treated with fluoride solutions, the F peak was detected in the wide scanning spectra of both of enamel treated with NaF and APF. The results of Ca/P, O/P and F/Ca ratios showed that fluorapatite was produced on the enamel surface by the NaF treatment, while CaF₂ was produced by the APF treatment. Futhermore, this CaF₂ had a somewhat low ratio of F/Ca and induced a P compound as compared with pure CaF₂2. These results showed that this CaF₂ is not pure, but rather CaF₂-like materials.
Based on these results, it is suggested that ESCA may be used to analyze the depth profile of chemical composition of enamel, especially, in the nm depth range, and to detect fluoride compounds which are produced on the enamel surface.