Aim: To assess the sealing ability of zinc oxide-eugenol (ZOE), Apexit, and Sealapex used as sealer-only backfills in root canals of primary teeth using the high-pressure replica technique.Methodology: Two hundred and seventy root canals of deciduous molars as well as primary anterior teeth were randomly assigned to three groups (n = 90). Root canals were prepared to size 35 and filled with either zinc oxide-eugenol (ZOE), Apexit, or Sealapex using a lentulo filler. Twenty-four hours after setting of the materials the roots were nail-varnished (except for the apical tip), and half of the specimens (n = 45) were penetrated by a coloured (rhodamine B) epoxy resin. The resin was infiltated into the pores and cavities of the teeth in a high-pressure vessel. The remaining groups (n = 45) were stored in 100% humidity, and infiltration of the resin followed after 40 d. Apical leakage was assessed by means of a grinding technique using eight steps of 0.5 mm each.Results: ZOE and Apexit failed to seal the root canals in both subgroups. This was significantly different from the root canals filled with Sealapex where in both subgroups some 30% of the specimens revealed a tight seal up to a distance of 2.9 mm of the apex.Conclusions: Under the conditions of this study it can be concluded that Sealapex shows less leakage than ZOE and Apexit. With regard to the three materials tested, Sealapex should be a viable alternative for sealer-only obturation of pulpectomized primary teeth. The high-pressure replica technique seems to be suitable for assessing leakage of root canal filling materials. (C) 2007 Elsevier Ltd. All rights reserved.

Selected experimental results are reported of the temperature dependence of the real part of the dielectric constant ε1 of sub- and supercritical mercury vapour relatively close to the critical point. The functional form of the temperature dependence of ε1 along isochores close to the critical isochore has a cusp-like anomaly near the critical temperature. The anomalous increase in ε1 reaches about 70% for mercury at densities very close to the critical density.

Variation of the unit cell parameters of Na2C2O4 is investigated by powder diffractometry in diamond anvils when hydrostatic pressure is increased to 6.5 GPa. Anisotropic distortion of the structure was observed up to about 3.8 GPa, whereupon a transition to an unknown polymorphous modification occurred. Before the phase transition, the compression was maximal in the direction perpendicular to close-packed layers formed by oxalate ions. Minimal compression was observed in the direction of the specific crystallographic axis b. The anisotropy of compression at elevated pressure is similar, but not identical, to the anisotropy of compression of the same structure at reduced temperature.

Effect of hydrostatic pressure on the two (I – monoclinic and II – orthorhombic) polymorphs of paracetamol was studied by X-ray diffraction in the diamond anvil cell at pressures up to 4.5 GPa (for the monoclinic form) and up to 5.5 GPa (for the orthorhombic form). The two groups of phenomena were studied: (i) the anisotropic structural distortion of the same polymorph, (ii) transitions between the polymorphs induced by pressure.

Results of X-ray diffraction and IR-specroscopy studies of the role of hydrogen bonds in the structural distortion of the monoclinic and the orthorhombic polymorphs of paracetamol induced by hydrostatic pressure (up to 4-5 GPa) are analyzed. Two groups of phenomena were studied: (i) the anisotropic structural distortion of the same polymorph, (ii) transitions between the polymorphs induced by pressure. The bulk compressibilities of the two polymorphs are practically equal. The anisotropy of pressure-induced structural distortion is qualitatively different. Lattice expansion in particular crystallographic directions was observed for the monoclinic polymorph. With increasing pressure the intermolecular NH...O and OH...O hydrogen bonds contracted and the intramolecular angles between the planes of the phenyl ring and the acetamide group decreased. Pressure-induced transitions between the polymorphs were poorly reproducible and limited by nucleation of the new polymorph.

Interesting results were obtained in the initial investigation of the nucleation behavior of supersaturated sulfur vapor up to temperatures above the transition. This is a second-order phase transition in liquid sulfur characterized by a change in molecular structure from closed sulfur rings to open radical chains within a narrow temperature range. Although the temperature dependence of the constant rate supersaturation is not correctly represented, it is surprising again how well classical nucleation theory describes experimental results even for such a complex substance. For homogeneous nucleation, there are indications that the gimel transition influences the nucleation behavior as a consequence of the changing thermophysical properties - density and surface tension - of the liquid sulfur. Photoinduced nucleation shows a striking effect directly correlated with the transition. Below the gimel temperature, the vapor is extremely sensitive to irradiation with light in the range 260-360 nm that decreases the constant rate supersaturation by about a factor of 10. At the transition temperature, the photo effect vanishes sharply. The close correlation of the structure of liquid sulfur and the nucleation behavior is interpreted as a confirmation of the capillarity approximation that indeed the properties of the liquid determine nucleation behavior.

The anisotropy of structural distortion of the monoclinic polymorph of acetaminophen induced by hydrostatic pressure up to 4.0 GPa was studied by single-crystal X-ray diffraction in a Merrill-Bassett diamond anvil cell (DAC). The space group (P2(1)/n) and the general structural pattern remained unchanged with pressure. Despite the overall decrease in the molar volume with pressure, the structure expanded in particular crystallographic directions. One of the Linear cell parameters (c) passed through a minimum as the pressure increased. The intramolecular bond lengths changed only slightly with pressure, but the changes in the dihedral and torsion angles were very large. The compressibility of the intermolecular hydrogen bonds NH ... O and OH ... O was measured. NH ... O bonds were shown to be slightly more compressible than OH ... O bonds. The anisotropy of structural distortion was analysed in detail in relation to the pressure-induced changes in the molecular conformations, to the compression of the hydrogen-bond network, and to the changes in the orientation of molecules with respect to each other in the pleated sheets in the structure. Dirichlet domains were calculated in order to analyse the relative shifts of the centroids of the hydrogen-bonded cycles and of the centroids of the benzene rings with pressure.

The first experimental study of the spectral dependence of the nucleation of cesium vapor caused by light absorption is carried out in a diffusion cloud chamber. The spectral dependence of the nucleation rate is compared with the absorption and ionization spectra of cesium vapor. The results evidence that the observed structure in the nucleation spectrum at photon energies above the ionization threshold is correlated to the light-induced ionization of cesium dimers Cs2+. At lower photon energies light-induced nucleation can be either due to generation of ions by direct ionization of cesium clusters, to various two-step ionization processes, or to optical excitation of cesium atoms. The spectral dependence of the nucleation rate provides a new and powerful tool to study ionization spectra of metal vapors. In addition to results obtained by conventional methods a more consolidated insight into energy levels of atoms and clusters under equilibrium conditions is possible.

The effect of pressure on the two polymorphs of [Co(NH3)(5)NO2]I-2 (phase I-orthorhombic, S.G. Pnma; phase II-monoclinic, S.G. C2/m) was studied by X-ray powder diffraction in a diamond anvil cell (DAC). In the presence of the ethanol-methanol-water mixture used as a pressure-transmitting liquid polymorph I was shown to undergo a phase transition at pressures between 0.45 GPa and 0.65 GPa. The diffraction pattern of the high-pressure phase (phase III) could be indexed as tetragonal with lattice parameters similar to those, which were previously reported for polymorph II in a 'pseudotetragonal setting'. The lattice distortions of phases II and III were studied at pressures up to 3.2 GPa and 3.7 GPa, correspondingly, and were shown to be very similar. Phases II and III were supposed to be very closely related. If poly(chlortri-fluorethylen)-oil was used as a pressure-transmitting medium, no phase transitions were observed in phase I of [Co(NH3)(5)NO2]I-2 at least up to 1.8 GPa (the point when poly(chlortrifluorethylen)-oil becomes solid), and the anisotropy of lattice distortion could be measured.

Variation of the unit cell parameters of paracetamol and phenacetin as a function of hydrostatic pressure was studied by X-ray diffractometry in diamond anvils. At elevated pressure (4 GPa), the crystal structures undergo anisotropic distortion. The greatest compression was observed in the directions in which the molecules are linked by van der Waals forces alone. Compressibility of the structures in the direction of hydrogen bonds depends on the presence of other types of interaction and on molecular arrangement in the crystals. In the case of paracetamol, integrated compression of the structure led to its stretching in definite crystallographic directions.

Photoinduced nucleation of mercury vapor is studied experimentally in an upward thermal diffusion cloud chamber. The rate of nucleation is greatly increased when the supersaturated vapor is illuminated with light absorbed by the vapor molecules. In analogy to ion-induced nucleation the photoinduced nucleation can be explained as a general effect for all condensing atoms or molecules forming long living electronically excited states.

The homogeneous nucleation behavior of supersaturated cesium vapor was investigated in a redesigned upward thermal diffusion cloud chamber in the temperature range between 359 K and 554 K. Critical supersaturations as a function of temperature were measured at temperatures between 359 K and 481 K. The critical cluster sizes (calculated using the Kelvin equation) varied between 12 atoms/cluster at 359 K and 40 atoms/cluster at 554 K. Nucleation rates as a function of supersaturation were measured at temperatures between 508 K and 554 K. The results obtained were compared to the internally consistent version of classical nucleation theory (ICCT). The critical supersaturations measured were about 2-fold larger at 554 K and about 10-fold larger at 359 K than theory predictions. The measured dependence of the nucleation rates on supersaturation was fit accurately by a power law and was weaker than theory prediction. The temperature dependent multiplicative correction to theory necessary for agreement with experiments was large, however, its temperature dependence was similar to that observed in measurements with n-alkanes.

The concentration of mercury in compressed argon and helium was determined in presence of liquid mercury in equilibrium, by measuring the near-u.v. optical absorption of the solution contained in a thermostated high-pressure cell. The absorbance of the 253.65 nm (6(1)S(0)-6(3)P(1)) resonance line of mercury perturbed by the presence of argon or helium atoms was integrated and correlated to the concentration of mercury in the fluid. Isothermal-solubility measurements were carried out within 298 K and 371 K to liquidlike densities. The saturation pressure of mercury in presence of fluid argon is found to be slightly higher than that corresponding to pure mercury at the same temperature; this solubility enhancement decreases for high fluid densities. On the other hand, the density of mercury atoms in the vapour phase in equilibrium with liquid mercury decreases when helium is present to high densities. The results show a qualitative agreement with the trends predicted by the thermodynamic model of L. Haar et al. - J. Chem. Phys. 52(10), 5069 (1970).

The homogeneous nucleation of supersaturated cesium vapor was investigated in a thermal diffusion cloud chamber operating in both the upward and the downward mode. In the upward operating mode, critical supersaturations were measured in the temperature range, 446–492 K. By operating the chamber in the downward mode, it was possible to circumvent experimental difficulties which arise at low pressures (due to phoretic effects) for the measurements made in the upward mode. Our previously published measurements on cesium were obtained in the upward mode in the temperature range, 421–554 K. These earlier measurements agree perfectly (to within their scatter) with the measurements presented here in the temperature range where they overlap, i.e., 421–492 K. The use of the downward mode enabled the extension of the temperature range of the measurements by 132 K towards lower temperatures. This makes cesium the substance whose homogeneous nucleation has been measured, in a thermal diffusion cloud chamber, over the largest range of temperatures, i.e., 289–554 K. The measured critical supersaturations were compared to the predictions of the Internally Consistent version of Classical Nucleation Theory and to the predictions of the Classical Theory.

Calculations are carried out to solve the thus far puzzling problem of the long-time trends in the photoinduced condensation of supersaturated vapors observed in thermal diffusion cloud chambers. These trends are the long-time delay of the condensation after switching the light on and the long-time decay after terminating the light. The calculations show that the supersaturation level which governs the condensation process cannot be affected significantly by irradiation under conventional experimental circumstances, and hence its change cannot be the cause of the long-time transients. These trends are attributed to the slow diffusion-limited growth of liquid droplets before they achieve the observable size of 10−3–10−2 cm. The predictions are in good agreement with experimental data.

The presence of a natural pore morphology is an essential factor in chemical and mechanical stability of teeth. Common histological methods give only an insufficient picture of the three-dimensional pore distribution in sound or carious teeth. This paper describes a new technique to obtain complete images of the pore structure in teeth or other biological hard tissues. Whole extracted human teeth from orthodontic therapy are mechanically cleaned and organic remnants removed chemically. After being (partly) dried, the teeth are penetrated by a freshly prepared and colored (rhodamine B dye) two-component epoxy resin. The resin is pressed into the pores and cavities of the teeth with pressures of up to 2000 bar in a high-pressure vessel by means of a manually driven piston screw pump for pressure generation. The resin fills all hollow spaces of the tooth down to sizes below 0.1 μm. The pulp and the root canals are cast in massive forms of the hardened epoxy resin, giving an exact replica of the natural structure. The penetrated samples in the form of whole, intact teeth are investigated microscopically so that the pore morphology of the tooth surface, including carious defects, can be examined. The structure of the pores extending into the interior of the tooth can be made visible by dissolution of the hard tissue-for example, in acid solutions. Micro-cavities filled with the resin are observed in thin, ground, and polished cross- and longitudinal sections cut from the teeth. The colored resin induces a high contrast to the dental apatite material. In fluorescence microscopy, only the resin structures are visible.