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The influence of fluoride, carbonate, and fluoride in combination with carbonate on the in vitro remineralization of bovine enamel was investigated with the use of a sandwich technique. After demineralization, enamel slices were subjected for 610 h to remineralizing solutions with 0.03 or 1.0 ppm fluoride. At each fluoride level, either 0, 1, 10, 20, or 25 mmol/L carbonate was tested. After 0, 22, 62, 126, 192, 329, and 610 h of remineralization, contact microradiographs were made by Cu Kα-radiation. At 0.03 ppm fluoride, carbonate had an inhibiting influence on remineralization. At 1.0 ppm fluoride, the inhibiting influence of carbonate changed into a stimulation of remineralization at 20 and 25 mmol/L carbonate. At 0, 1, and 10 mmol/L carbonate, fluoride had an inhibiting influence on remineralization. The differences in remineralization between the groups were explained by events concerning crystal growth, i. e., different types of minerals might have precipitated with differences in precipitation rates, and retardation of a precipitation step might have occurred under the various remineralization conditions. There was a mutual influence of fluoride and carbonate on the remineralization process. We conclude that the composition of the remineralizing solution with respect to fluoride and carbonate concentrations is important for the remineralization process.

Previous studies have shown that rat incisor dentin contains a considerable amount of magnesium that is distributed heterogeneously. The cementum-related dentin, especially its incisal portion, is richest in magnesium. It was the purpose of the present study to investigate the changes that occur in the magnesium content during dentin maturation. Cross-sections were prepared from rat incisors at the apical, middle, and incisal levels. By means of an electron microprobe, tracings were made of the Ca-, Mg-, and P- signal frequencies. Comparison of corresponding dentin layers within and between the cross-sections showed that the Mg/P molar ratio was always higher in the cementum-related dentin (CRD) than in the enamel-related dentin (ERD) and increased from the apex toward the incisal edge. Especially in the incisal cross-section, an increase in Mg/P was found from the older (peripheral) toward the younger (central) dentin layers. As the Mg/P ratio varied from 0.07 to 0.33, the Ca/P ratio was found to fluctuate from 1.48 to 1.15. The two ratios appeared to be highly correlated (r = -0.97; p

The morphology of dentinal cavity walls, wetting by poly (methyl methacrylate), and resistance to tensile forces was studied with a scanning electron microscope, before and after etching or fixation, or both, with glutaraldehyde. Results indicated that the surface layer of dentinal cavity walls after etching is of an aqueous-organic nature, that glutaraldehyde fixation improves the mechanical properties of the surface layer of the cavity wall, and that wetting by poly (methyl methacrylate) is effective.

Intact roots of human molars, which had not been exposed to the oral environment, were exposed to buffer solutions of pH 5.5, which contained, besides calcium and phosphate, various concentrations offluoride. Densitometric measurements on contact-microradiograms of transverse sections of these roots produced data which were used to calculate the rate of demineralization ( Vdem). Vdem appeared to be reduced with increasing fluoride concentration and with decreasing pIOHA (i.e., the negative logarithm of the ionic product of hydroxyapatite) of the buffer solution. In addition, it was observed that, after some days of exposure, remineralization started to occur within the surface layer at some μm from the outer surface and that the region within which remineralization took place was extended inward with increasing time of exposure. These data suggest that fluoride is effective in the prevention of root surface caries. The mechanism of the interaction of fluoride with the root mineral is discussed.