Permeability of 3 types of nonelectrolyte (acetonitrile: AN, ethyleneglycol: EG, and glutaraldehyde: GA) through a Ca-Alg gel membrane was investigated. Change in concentration of solutions occurred betweens solution and deionized water separated by a gel membrane. The diffusion speed of solute with a lower molecular weight was large. The gel membrane did not show semipermeability for AN, and the solutions reached equivalent concentration quickly. An apparent osmotic pressure effect was observed in EG and GA, which was marked regarding the latter. From these results, it is estimated that Ca-Alg gel immersed in GA solution would cause syneresis due to a kinetic osmotic pressure effect, however, gel shrinkage due to crosslinking was large. And it is estimated that it is not easy to produce gel shrinkage in the solutions with small kinetic osmotic pressure effect like AN and EG.

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This study examined the joint strength of temporary cements between titanium alloy plates and gold alloy. Six commercially available temporary cements (2 polycarboxylate cements, 1 paste-mix type cement with eugenol and 2 without eugenol, and 1 powder-liquid type zinc oxide-eugenol cement) and a luting cement (as a control) were used. The cylindrical gold alloy was adhered to the titanium alloy surface using each cement. The specimens were kept in a moist atmosphere at 37℃ for up to 28 days. The joint strengths of cements were measured by shear bond test at 7 or 28 days after the start of mixing. Paste-mix type cement without eugenol showed a significantly greater joint strength among the temporary cements tested. One of the temporary polycarboxylate cements did not retain the alloy cylinder. The joint strength of eugenol cement at 28 days was significantly lower than at 7 days. The luting cement (control) exhibited a greater joint strength than the other temporary cements tested.

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Bisphenol-A is widely used as a component of monomers for resin-based composites and sealants used in dentistry. Bisphenol-A can leach in the surrounding tissues after digestion of the unpolymerized resin monomers with esterase and has the potential to cause irritation, inflammation, and an allergic response. Hence, we examined the adverse effects of bisphenol-A using human dental pulp cells (D824 cells). Bisphenol-A reduced the growth and recover rates of D824 cells. It also decreased the rate of incorporation of [³H] proline into acid-insoluble fractions and the expressions of mRNA and protein for bone sialoprotein. Our findings indicate the possibility that bisphenol-A affects the growth and differentiation of human dental pulp tissue.

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Delayed fracture of medical Ti devices was studied by micro-mechanics. Effects of oxygen and hydrogen on the characterization of titanium were discussed in terms of macro and microscopic aspects. Hydrogen can have a major effect on the microstructure and properties of Ti. When the hydrogen concentration exceeds the terminal hydrogen solubility, a titanium hydride phase (TiH₂) can begin to form. Transformation from α-Ti to the hydride phase results in a volume expansion. Hydrides are formed along the grain boundary deeply in the surface. Micro-cracks are formed on the hydrides when an external force is applied. The cracks are developed and accelerate by the mechanism of stress-corrosion cracking related to hydrogen. Experimentally, we confirmed this by fatigue tests of pure Ti and by delayed fracture tests under sustained tensile loading in fluoride ion solutions. The results indicate that stress-corrosion cracking is an effective factor in delayed fracture of Ti.

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