A new apparatus for the de- and remineralization of enamel in vitro under constant composition conditions is described. A de- or remineralizing solution flows over the specimens at a controlled rate. During artificial lesion formation (using an acetate buffer containing methylhydroxydiphosphonate, MHDP), the composition of the solution is constant. The Ca and phosphate variation is less than 3%, pH variation is less than 0.03 pH unit. For enamel these variations are within the biological variations between enamel specimens. Experimentally it was found that the liquid streaming over the enamel surface does not measurably remove material from the surface (erosion) with the experimental error of 0.1 μm. This was measured by following microhardness indentations during demineralization. The effect of various MHDP concentrations on demineralization was investigated in the range of 2–50 μM. Even low concentrations of MHDP prove to be effective in the microhardness increase and lesion depth reduction during demineralization. In the demineralization experiment it is shown by means of microradiography, hardness measurements as well as light microscopy that the method described quickly produces reproducible lesions. In a remineralization experiment of demineralized enamel effective remineralization of the lesions occurs in 360 h, giving a threefold increase in microhardness and a twofold decrease in lesion depth.

In this study the effect of X-ray irradiation on demineralization of bovine dental enamel in vitro was investigated. Enamel specimens were irradiated with 72 Gy and subsequently demineralized (140 h) under reproducible constant composition conditions at pH = 5 in the presence of methylhydroxydiphosphonate (MHDP). Microhardness measurements after demineralization without MHDP showed significant differences (p < 0.001) between irradiated and nonirradiated enamel specimens; no significant differences were found in the presence of MHDP. Quantitative microradiography showed that both mineral loss and lesion depth were significantly lower (p < 0.001) for the irradiated enamel specimens compared with the nonirradiated ones. Surface layer formation was observed in irradiated enamel demineralized in a solution without MHDP. It was shown that X-ray irradiation decreased the enamel acid solubility in vitro.

respectively. All P-Au vectors point approximately to the center of the cluster with normal P-Au distances (2.27 ± 0.09 A). Physical data including 197Au Mossbauer and (solid-state) 31Pj'H) NMR are reported. [Au7L7]+ can also be observed during the reaction of L with the novel compound [AugL6I]PF6. The latter cluster could be prepared from the reaction of [Au9Lg]3+ with Bu4NI. The intermediacy of the title compounds in the formation and reactivity of gold cluster compounds will be discussed.Synthesis, Structure, and Magnetic Properties of Fluoride-Bridged Copper(II) Dimers. Crystal and Molecular Structures of Bis(^-fluoro)bis[tris(3,4,5-trimethylpyrazole-iV1 2)copper(II)] Bis (tetrafluoroborate) and Bis(^-fluoro)bis[(5-methylpyrazole-JV2)bis(3,5-dimethylpyrazole-Ar2)copper(II)] Bis (tetrafluoroborate)

The aim of this article was to investigate the effects of methanehydroxydiphos-phonate (MHDP) and fluoride (F) separately and combined, on the demineralization process in enamel and in dentine under constant composition conditions. The demineralization was carried out in solutions containing 3 mM calcium, 3 mM phosphate, pH = 5.0, and either 6 μM MHDP, 12 μM F or 6 μM MHDP and f 2 μMF. After demineralization periods (t) between 24 and 140 h, the lesion depth 1 and the mineral loss ΔZ were measured by transverse microradiography of the enamel and dentine speciments. The amount of mineral lost during demineralization averaged over the lesion depth, R = ΔZ/1, was calculated. R ≈ 17 vol% for both enamel and dentine, both ΔZ and 1 being greater for dentine than for enamel by approximately the same factor. The results show that under the same conditions dentine is attacked much more strongly than enamel. The lesion progress with time is quite different for the two tissues: in enamel the lesion depth progresses als l3 = αt + β, in dentine as l2 = α’t + β‘. The slopes α and α’ decrease in the order MHDP > F > MHDP + F. In enamel the combined inhibitor effect is only slightly larger than the effect of F alone; in dentine the inhibiting effects of F and MHDP are approximately additive. The inhibitor interactions can be described by the Langmuir adsorption theory. For the adsorption of F onto enamel the adsorption constant K_kin was calculated to be 5.2 × 10⁴ liters/mol, about an order of magnitude smaller than the corresponding value for hydroxyapatite. For adsorption of MHDP onto enamel, K_kin was found to be 1.0 × 10⁴ liters/mol, which is in the same range as the corresponding value for hydroxyapatite.