The application of temporary cement on the tooth surface had an inhibitory effect on the adhesiveness between teeth and resin cements.We analyzed the influence of the remaining temporary cement on the adhesion, determining the adhesive strength of a resin cement to dentin.Bovine dentin was divided into several groups exposed to different temporary cements for 24 hours.Thereafter, the temporary cement was completely removed with an excavator.The adhesiveness of resin cement(Panavia 21, Kuraray Co.)to this surface was measured following a 24-hour storage in water at 37℃, and its interfacial layer was analyzed by SEM.The results showed an adhesive strength of 3.6MPa on the surface pretreated with HY-Bond Temporary Cement(Shofu Co.), 4.9MPa with Freegenol Temporary Pack(GC Co.), and 5.3MPa with Tempack(Westward Co.), all lower than the 6.9MPa, presented by the control group.The SEM images of the interfacial layer revealed a hybrid layer of 0.5μm in thickness, in the control specimens whereas no hybrid layer existed on the specimens treated with temporary cements.

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Recently a gallium alloy without mercury has been developed instead of dental amalgam and they have already been commercialized.In the present study, the corrosion resistance was investigated to obtain useful information to improve corrosion resistance of the gallium alloy by using corrosion series tests;immersion test, cyclic voltammetry, and observation of secondary electron image and analysis of corresponding elements by means of an X-ray microanalyzer.Corrosion processes of the gallium alloy in 1% sodium chloride solution released the gallium ion from ring reaction layer around the core at first, and then selective release of tin ion and indium ion occurred from the matrix.

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In this study, the properties of metal castings obtained from commercial gypsum-bonded investments for the quick heating method were investigated.Three gypsum-bonded investments for the quick-heating method and two conventional gypsum-bonded investments were employed;dimensional accuracy, surface roughness, surface hardness and tensile properties of Ag-Pd-Cu-Au alloy castings obtained from these investments were examined.No casting fins were observed on the casting surfaces.Dimensional accuracies of the castings were varied with the investment used.Surface roughness values were similar except for one conventional investment.Micro-vickers hardness numbers of the castings obtained from the quick-heating investment were slightly smaller than those from the conventional investments.Tensile properties, such as tensile strength, proof strength, elastic modulus and elongation showed no differences among the castings.These findings suggested that there were no obvious differences between the properties except for the casting accuracy of the castings obtained from the quick-heating and those from the conventional investments.

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Octacalcium phosphate[Ca_8H_2(PO_4)_6・5H_2O, hereafter referred to as OCP]was synthesized at 30〜80℃ by the reaction of an aqueous suspension of dicalcium phosphate dihydrate(DCPD)and calcium carbonate.Thin blade crystals of OCP were formed on the crystal plate of DCPD, and were converted to hydroxyapatite(HA)as time elapsed at 50〜80℃.The converted HA was calcium-deficient hydroxyapatite with a Ca/P ratio of about 1.5.The X-ray diffraction intensities during decrease of DCPD and increase of both OCP and HA changed proportionally to the square root of reaction time and these change rates depended upon the reaction temperature.These findings suggest that the rate-determining step of this successive reaction is the diffusion of calcium ions through the Nernst boundary layer around each crystal particle.

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Calcium orthophosphates, i.e, rhenanites of a type of ACaPO_4, in which A=K, Na, or Li, were prepared and their physicochmeical properties were investigated thermomechanically, by x-ray diffraction and infrared spectroscopy in an attempt to investigated their effects on sintering of hydroxyapatite.Thermomechanical analysis suggested that of the rhenanites, NaCaPO_4 and LiCaPO_4 accelerate the sintering of hydroxyapatite, lowering the sintering temperature.As compared to NaCaPO_4, LiCaPO_4 was much more effective in lowering the sintering temperature.The differential thermal analysis suggested that its effectiveness in lowering the sintering temperature of hydroxyapatite is related to the fact that LiCaPO_4 melts to from a liquid phase at a temperature of about 840℃.At 4wt% of LiCaPO_4 added, the hydroxyapatite could be sintered at temperatures around 780℃, which is approximately 300℃ lower than that used for sintering non-additive hydroxyapatite.

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An experimental low speed cutting saw equipped with a torque transducer was constructed.The cutting torque on composites with various cutting loads was measured during cutting.The total amount of cutting work on the composites was calculated from the torque measured.The loss volume of the composites was also calculated from the weight loss before and after cutting, and from the density of the composites.From these findings, the cutting work on the composites per unit loss volume was estimated.For posterior composite resins tested, the cutting work was about 130〜150J/cm^3, at the cutting load of 350gf in this cutting saw.

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Acids sometimes modify the collagen in the demineralized dentin which collapses easily during the drying process. The collapsed dentin does not permit monomer impregnation which makes preparation of hybridized dentin difficult. SEM examinations of the prepared dentin which has been protected with a protective varnish and the newly formed hybridized dentin after soaking bonded specimens in HCl and then in NaOCl give information on the bonding of resin to dentin, that is, the creation of hybridized dentin. It was concluded that the shrinking of the deminearlized dentin depends on the etching period, concentration and dissociation constant of the applied phosphoric acid.

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The cytotoxicity of commercial denture lining materials to a tissue model (MATREX) which is an in vitro reconstructed cell culture system, was tested and evaluated by the lactate dehydrogenase and MTT assay. Eight cold-curing acrylic materials yielded strong cytotoxicity to the tissue model. However, the heat-curing type was hardly cytotoxic. A silicone material showed moderate cytotoxicity and a fluorine-containing material slight cytotoxicity. On the other hand, three light-curing type materials showed moderate to strong cytotoxicity prior to light irradiation, which decreased cytotoxicity. The results of cell recovery after exposure of extracts of the cold-curing acrylic materials remained low to moderate. The heat-curing acrylic material did not affect the cell recovery. The silicone material showed moderate cell recovery and the fluorine-containing material a slightly higher rate of cell recovery. The light-curing type materials had a similar effect on cells in the tissue model. Cell recovery was similar in three repeated extractions of materials. Some suggestions might be given in in vitro testing of materials in close contact with the oral mucous membrane, as are denture lining materials.

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