The effect of a tannin-fluoride mixture on human dental enamel

In this study, the effect of a tannin-fluoride mixture (Ta-F, 0.5% tannic acid, 450 ppm fluoride, pH 5.9) on dental enamel has been investigated by using scanning electron microscopy (SEM), electron probe microanalysis (EPMA) and X-ray diffraction (XRD), compared with the effect of acidulated phosphate fluoride (APF, 0.015 M phosphoric acid, 450 ppm fluoride, pH 5.3). Under the SEM, a large number of spherical globules (1-5 microns in diameter) were observed on the enamel surface treated with Ta-F. On a fractured cross section, these large globules showed a columnar appearance, measuring 2.5-5 microns each in height. They had a good range and formed a single coating layer on the enamel, whereas on the APF-treated enamel only very small spherical globules 0.1-0.5 micron in diameter were seen. Moreover, three types of connective patterns were observed between the basal ends of these columnar deposits and the enamel surface: (a) a pattern loosely attached to the enamel surface, (b) a pattern partially connected with the crystals of enamel, and (c) a pattern inserted into the pores of enamel. These columnar deposits also showed very strong resistance either to acid decalcification or to water washing. By EPMA and XRD examinations, a remarkable elevation of the fluoride profile accompanied by a high elevation of calcium was observed and CaF2 peaks were detected on the enamel surface. These results suggest that the columnar deposits might contain the CaF2-like substances and possess unique morphological and qualitative features which are quite different from the deposits found after APF or NaF treatment as described in previous studies.