The changes of mineral content in surface enamel and artificially formed enamel fissures were investigated by pH cycling. Lesions were produced on sound enamel with artificially formed fissures by a 12-hour immersion in 0.1 M lactic acid buffer containing 120 ppm Ca, 55.8 ppm P, 1% CMC, adjusted to pH 4.5 at 37°C. The samples were divided into three groups. The control group received no further treatment. The other two groups were subjected to two different pH cycling systems: (1) a 20-hour immersion in remineralizing solution containing 120 ppm Ca, 55.8 ppm P, 150 mM NaCl, adjusted to pH 7.0 at 37°C plus a 4-hour immersion in the same latic acid buffer used before [F (-) grop) ; and (2) the same alternating of de-and remineralization as (1), but the remineralizing solution contained 3 ppm F (F (+)-) group].
The results showed little change of mineral content in the fissure enamel. However, large mineral loss in the surface enamel was found by quantitative microradiographic evaluation. Microradiographic pictures of the remineralized enamel surface in the F (+) group showed lamination structure. The degree of inhibition of mineral loss were much higher in the F (+) group of the remineralized enamel surface than in the F (-) group. Furthermore, an increase of mineral content was observedin the shallow part of the enamel surface in the F (+) group.