Search

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.

Crowns and roots of human molars, the roots from which had not been exposed to the oral environment, were exposed for 0, 3.5, 7, and 14 days to buffer solutions which were undersaturated or supersaturated with respect to hydroxyapatite. Densitometric measurements on contact-microradiograms of transverse sections of the crowns and of the cervical parts of the roots yielded plots of the mineral content as a function of the distance to the outer surface. From these plots, the rate of demineralization was calculated. It was found that the mineral of the roots dissolved even in buffer solutions which were supersaturated with respect to hydroxyapatite. Comparison of the results obtained from the crowns with those from the roots showed that the root hard tissues were more vulnerable to demineralization than was the dental enamel.

Roots of extracted human molars were treated for both 10 and 30 min with a saturated solution of dicalcium phosphate dihydrate (DCPD) of pH 2.4 and subsequently with a 5.3 mmol.L -1 solution of sodium fluoride of pH 7.0. The objective of these combined treatments was to convert the highly-soluble root mineral into the less-soluble fluoridated hydroxylapatite, with DCPD as an intermediate, to improve caries resistance. The mineral content of the surface layer was not affected in a significant way. Roots treated in this way were subjected to 50 mmol.L-1 acetate buffer solutions of pH 5.5 and with pIOHA-values of 112, 116, and 122. The proportional reduction of the rate of demineralization (Vdem) of similarly treated roots subjected to buffer solutions of pIOHA 112 and 116 appeared to be equal initially. Since fluoridated hydroxylapatite is insoluble under these conditions, these findings are in agreement with expectations. The reduction of Vdem amounted to about 45 and 70% for roots treated for 10 and 30 min, respectively. When roots were treated for 10 and 30 min and then exposed to buffer solutions with a pIOHA 122, reductions of Vdem of about 30 and 55%, respectively, were found. Conversion of the root mineral into fluoridated hydroxylapatite can eliminate, in principle, the existing difference in caries susceptibility of the root and of the dental enamel.

Fluoride specifically adsorbed to hydroxyapatite reduces the rate of dissolution of hydroxyapatite. Since specific adsorption is a property which anions of all weak acids have in common, it is expected that the anions of lactic and acetic acid will be specifically adsorbed to hydroxyapatite too and in this way will cause a reduction in the rate of dissolution of hydroxyapatite. In order to investigate this, we used the experimental results from Featherstone and Rodgers (1981). Calculations of the rate of increase of the lesion depth in dental enamel per mmol. L -1 of the un-ionized acid revealed that lesion progress was pH-dependent and was lowest at that pH which corresponds with the pK-value of the relevant acid. It is concluded that the anions of lactic and acetic acid are specifically adsorbed to the enamel mineral and in this way reduce the rate of dissolution of the mineral. This suggests that a description of the development of an artificial caries lesion in mathematical terms should include the effect on the rate of dissolution of the mineral of specific adsorption of the relevant acid anions to the mineral.

A new equation is proposed for the description of the static creep of dental amalgam. It is satisfactory for a wide range of stresses and strain rates in static creep experiments during steady state. The hypothesis was confirmed that creep of dental amalgam is determined by the low melting phases.