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In vitro enamel demineralization was studied in undersaturated calcium phosphate solutions containing fluoride in the concentration range 0–10 ppm. Depending on the fluoride concentration either erosi

Most of the fluoride acquired during topical applications will be released in the oral environment. This investigation deals with the effectiveness and retention of fluoride after different treatments of the enamel. The effect of acidified phosphated fluoride (APF) on sound, and etched, and neutral KF on etched enamel were investigated by studying the F profiles in the enamel after 0, 1, 2, 4 and 8 weeks exposure to running tap water. APF application on etched enamel showed the deepest fluoride penetration and retention. At 8 weeks the differently treated enamel samples were exposed to an artificial caries-inducing solution. The etched and subsequently APF-treated enamel showed least release of minerals.

Mineral loss and uptake in artificial enamel lesions was investigated by pH cycling: samples were subjected to a sequence of de- and remineralizing solutions. The ratio between de- and remineralization per day and the presence of fluoride in the remineralizing solution were varied among different experimental groups. Calcium, phosphate and fluoride uptake and loss were measured. The lesions were also studied with a hardness tester and micro radiography. The results show a difference in remineralization mechanism between continuously remineralized and pH-cycled samples (with respect to Ca/P ratios). With fluoride present, after some time, ‘arrested’ carious lesions are formed, which can hardly be further demineralized or remineralized. This is in agreement with clinical findings of remineralization in areas with fluoridation of the drinking water.