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Summary The main problem in interpreting birefringence of dental enamel under polarizing microscopy is the lack of physical constants able to allow the Wiener equation to be applied directly to the composition of such tissue. The present study introduces a new approach to circumvent this constraint. Because the nonmineral phase of enamel is heterogeneous, its refractive index can be computed in terms of its components (namely, water, which is partially replaced by the immersion medium, and organic matter), thereby providing a more acceptable refractive index to be used in the Wiener equation. Furthermore, the enamel mineral volume is ordinarily calculated on the basis of the density 3.15 g cm−3. The density 2.99 g cm−3 has been, however, reported to be more accurate for enamel hydroxyapatite, so enamel mineral volumes from selected published data were converted using such a density. The birefringence of mature enamel computed by the Wiener equation, taking into account the above refinements, matched, for the first time, published experimental birefringence values. The theoretical water and organic contents were also consistent with published experimental data. Thus, a direct application of the Wiener equation to the enamel composition has now been achieved. It is speculated that quantitative data on the mineral, the water and the organic contents of mature dental enamel can be derived from interpretation of birefringence in two immersion media (obtained before and after extraction of the organic matter) with this new approach.

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Application and development of new methods in caries prevention is of paramount importance to reduce the incidence of chronic cases of the caries disease and to preserve dental structure. In this work, we tested nanosecond pulsed Nd:YAG laser on enamel surface examining the changes laser-induced by means SEM, EDS, and FTIR. SEM revealed, the existence of melted zone and bubble inclusions when 40 J/cm2 (τ=6 ns, 5 Hz) was applied on human sound enamel surface. The morphological alteration to 10 J/cm2 (τ=6 ns, 5 Hz) and to 20 J/cm2 (τ=200 ns, 7 Hz) no presented melting aspect, but a greater number of bubble inclusions. We have indicated that the Ca/P ratio increased to irradiation conditions employed here. In our previous study, the combination of the laser parameters not produce an excessive increase in temperature. The temperature variation was less than 2.5°C in the dental pulpal, following application of the energy density of 40 J/cm2. Our results suggest that nanosecond pulsed Nd:YAG laser can be used to obtain minimal morphological alteration associated with a chemical reorganization enhancing the microhardness values and consequently inhibiting the acid dissolution by bacterial agents. In this work, the Vickers microhardness was quantified. Our results of FTIR analysis indicated that the laser effects occurring substantially in the organic compounds (such as water and proteins groups) and are reduced for mineral contend (such as phosphate and carbonate groups).

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An experimental investigation of the coherent interaction of femtosecond pulses with two resonant sequential transitions of Rb atoms is presented. Fluorescence from the atomic system exhibits beating at a frequency given by difference in the sequential atomic transitions. The results are interpreted in terms of quantum interference in the induced coherence and its interaction with the field that results from a cooperative emission process.

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