The relative efficacy of fluoride toothpastes assessed with pH cycling.

This study addressed the dose response between fluoride toothpastes and in vitro de- and remineralization, to predict the efficacy of toothpastes and understand the mode of action in the range 0-3,000 ppm F. Enamel lesions were pH-cycled with calcium uptake and loss being assessed daily. Both 'shallow' (about 50 microm deep) and 'deep' (about 200 microm deep) lesions were studied. F treatments were given in 30 (w/v)% toothpaste dilutions for up to 5 min daily. Calcium loss during the demineralization periods showed a dose response, resulting in 72% reduction for 3,000 ppm F compared to 0 ppm F. Calcium uptake during remineralization was increased in the F compared to non-F groups, with F concentration being less important than its mere presence. Significant differences were observed in F response between shallow and deep lesions, suggesting that this parameter should be included when testing caries-preventive products. Microradiographic analysis showed that lesion depth and severity had increased significantly in the non-F groups. In the F groups, the original lesion was partly remineralized, while a new lesion had formed beyond the original lesion front. Mineral loss of this second lesion correlated inversely with the F concentration of the treatments. These data revealed that fluoride can drive demineralization further into enamel by making the surface tissue less soluble, hence by not neutralizing acids penetrating into the tissue. It is also concluded that depth analysis of mineral uptake and loss is important to understand the mode of action of different F products.