Method: Enamel surfaces of the test teeth were ground to remove its outer 50 µm, and then covered by nail varnish except for a 2 x 1 mm window. The specimens were treated with 1% potassium malate buffer (pH 5) solution containing 500 ppm fluoride as NaF, for 5 minutes, 8 times a day. Rest of the time, teeth were reserved in artificial saliva (pH7). This cycle treatment was carried out at 37ºC for 14 days. After the treatment, the specimens were sliced longitudinally and observed by optical microscope and X-ray microradiography. Fine structures of enamel surface and subsurface were observed by scanning electron microscope (SEM: Hitachi S-4000). Fluorine distribution on enamel surface and subsurface areas were detected by Time-of-flight secondary ion mass spectrometry (TOF-SIMS: ION-TOF TOF-SIMS IV). Total amount of the fluoride intake of the exposed area was measured by ion-selective electrode after extracted by perchloric acid.
Results: Opaque layers were observed at the subsurface area of enamel under the exposed area of the sliced specimens, whereas demineralization was not detected by X-ray microradiography. TOF-SIMS results showed that fluorine was localized like a mesh structure under 20 µm from surface. The fluoride intake of the exposed area was 9µg/mm3.
Conclusion: TOF-SIMS images suggest high fluoride concentration in enamel rod sheaths after the treatment. Although it can not be a direct evidence, high fluoride intake of the exposed area could suggest formation of calcium fluoride like materials, which is known as a major product of acidic fluoride treatment on enamel. The light scattering between enamel rod body and fluoridated sheath layer could be occurred and thought as a cause of the opacity layer of enamel.