Mineral density and fluoride content of in vitro remineralized lesions

This in vitro investigation studied the remineralization of experimental caries lesions in bovine enamel by use of three methods: (1) surface microhardness, (2) microradiography, and (3) abrasion biopsy for mineral density and fluoride content. The lesions were produced by a two-day exposure to 0.01 mol/L lactic acid/sodium hydroxide buffer partially saturated with 3.0 mmol/L Ca, 1.8 mmol/L P, in 1% CMC, at pH 4.0 and 37 degrees C. The lesions were exposed to a remineralizing solution containing 3.0 mmol/L Ca, 1.8 mmol/L P, and 3 ppm F in 1% CMC at pH 7.0 and 37 degrees C for two, six, and ten days, with solution changes every two days. The data derived from the three methods are presented in sequence from the baseline and at days two, six, and ten of the remineralizing treatment. Microhardness measurements showed hardness recoveries of 35.9, 78.9, and 87.5%, respectively. Microradiography suggested complete recovery with the ten-day remineralization. Abrasion biopsy of successive 10-micron layers to a depth of 100 micron indicated 15.2, 39.8, and 68.8% mineral density recoveries, with fluoride content of the surface layer increasing from a baseline of 300 ppm to 4600, 9000, and 9800 ppm F for the 2, 6, 10 days of remineralization, respectively. Subsequent acid-etching of thin sections from the ten-day-remineralized specimens showed that the fluoride-enriched remineralized area was more resistant to acid dissolution than was the underlying normal enamel.