The objective of this study was to determine the physical and mechanical properties of tetracalcium phosphate cements containing chitosan powder, as well as the tensile bond strength to human dentin surface.
Six different tetracalcium phosphate cements with varying chitosan concentrations (0, 0.5, 1, 5, 10 and 20 wt% in powder) were prepared. These experimental cements were mixed with a citric acid-malic acid aqueous solution at a powder-liquid ratio of 1.5 (g/g). The setting time (37℃, 95±5%, r.h.), the compressive strength (24 h) and the solubility and disintegration (24 h) of these cements were measured according to the methods outlined in ADA Specification No. 61 for zinc polycarboxylate cement. The tensile bond strengths of these experimental cements to human dentin surface were determined by the methods previously described.
The setting time decreased with increasing concentrations of chitosan up to 1 wt%; however, the setting time was prolonged when the concentrations of chitosan exceeded 5 wt% in powder. The compressive strengths of the cements significantly (p<0.05) decreased with increasing concentrations of chitosan powder. In contrast to the strength, the amount of solubility and disintegration significantly (p<0.05) rose with increased chitosan concentration. No significant (p>0.05) differences in the tensile bond strengths of the cements to human dentin surface were found among all cements tested.
This study showed that a new tetracalcium phosphate cement can be made by incorporating chitosan into cement powder. The results also indicated that for this new cement to be used as a base and lining material, the maximum concentration of chitosan in the powder which allowed adequate physical and mechanical properties is 1 wt%.

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The objective of this study was to examine the effect of different powder-liquid ratios and surface treatment agent on the wettability and bond strength of glass ionomer cement for restorative filling to human dentin.
The wettability and tensile bond strength of conventional or light-cured glass ionomer cements for restorative filling to human dentin were measured according to methods previously described.
A significant correlation (r=0.983, p<0.05) was found in the light-cured glass ionomer cement between the powder-liquid ratio and the measured contact angle; however, there was no significant correlation (r=0.154, p>0.05) in the conventional glass ionomer cement between the variables. Significant correlations between the powder-liquid ratio and tensile bond strength were observed in both conventional (r=0.978, p<0.05) and light-cured glass ionomer cement (r=0.933, p<0.05).
Although the contact angle of both cements to human dentin did not show remarkable change after the application of a surface treatment agent to the human dentin surface, significant increases in the tensile bond strength were found in both types of glass ionomer cements.
The results of this study suggested that the application of dentin surface treatment was an effective procedure to increase the bond strength of glass ionomer cement for restorative filling to dentin.

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To clarify the casting properties of a one chamber casting machine, defects and titanium flow in the castings were examined by transparent X-ray photographs and a flow visualization technique. The results were compared with those obtained previously using a two chamber machine. Flow observations showed that the inflow of the fomer machine was faster, due to the higher pressure (7 Kg/cm²) applied suddenly. In a thick cavity, turbulent flow sometimes occurred and in such a case many large internal defects were generated because solidification of the shell finished later than that of laminer flow. In a thin cavity, external defect occurred because the filling times were longer than those of pressure elevation in the cavity due to the diffusion of argon. In both types of cavity, almost complete castings were sometimes obtainid. This uncertainty was caused from the indeterminate permeability of cavity wall. In a complicated cavity consisting of thick and thin portions, internal defect in the thick area and external defect in the thin area were observed.

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A Press-forming method was studied for glass in the system based on CaO-MgO-SiO₂. The softening temperature of glass with a diopside composition (CaO・MgO・2SiO₂) was 832℃. This glass shows good viscous flowability at 830〜880℃. The strain rate under 850℃ was 1.3 mm/min at 0.35 MPa. A press-forming furnace was designed for the semi-automatic press forming and crystallization. Glass ingots 10 mm in diameter were formed and crystallized under 5 kgf at 840〜860℃ for 30〜50 min in the conventional quartz investment. The glass ingot can be pressed into a sheet (0.36 mm thick), meshes or dental MOD inlay shape under pressure of 0.64 MPa.

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Thiobarbituric acid monomers, 5-ally-2-thiobarbituric acid (5AS) and 5-(4-vinylbenzyl)-2-thiobarbituric acid (5VS) were utilized for surface treatment of dental metals to improve the adhesion of MMA-PMMA/BPO-amine resin. The agents were prepared by dissolving 5AS or 5VS in solvents such as methyl methacrylate, acetone and ethanol. Seven kinds of dental metals were employed as an adherend. After applying the treatment agent to the surface of the mirror-polished adherend, the specimens were allowed to stand for one day. Thiobarbituric acid remaining on the surface was washed off with acetone prior to the application of resin when the concentration of thiobarbituric acid in the agent was high, i.e., 1.0 mol%. Two specimens of each metal were butt-jointed together with the resin. Tensile bond strength was measured after 2,000 thermal cyclings in water at temperatures of 4 and 60℃. The agent containing 5VS was more effective than that containing 5AS in all cases. The use of 5VS agent effectively enhanced the bond strength of the resin to gold-silver-palladium alloy or silver alloy at low concentrations of 0.001 mol% or 0.01 mol%, respectively. The bond strength of MMA-PMMA/BRO-amine resin to nonprecious alloys or titanium treated with 0.01 mol% of 5VS was higher than that with 0.001 mol% of 5VS, contrary to the case of the resin cured by TBBO initiator.

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Metal injection molding (MIM), a relatively new process, makes molding metal easier and can be used to make complicated, three dimensional shapes with great precision. In this study, mechanical properties of sintered titanium samples using MIM were investigated and compared with the original titanium to propagate the application of highly biocompatible titanium in the field of dentistry. The main results obtained were as follows;
1) SEM observation of sintered titanium samples using MIM revealed many spherical and separated pores, 2) The tensile strength, three-point bending strength, proof stress, and Vickers hardness of sintered titanium samples using MIM were higher than those of the original titanium, 3) Elongation of sintered titanium samples using MIM was one third of the original titanium, 4) Vickers hardness fluctuation of sintered titanium samples using MIM was greater than that of the original titanium, 5) It was considered that MIM, a unique process for metal, could be applicable to dentistry.

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To collect basic data for application of Ti-6Al-7Nb alloy in dentistry, castability and mechanical properties were investigated using specimens made by usual dental casting technique. Good castability was seen when the specimen was made using a magnesia mold and a centrifugal casting machine. The alloy of Ti-6Al-7Nb showed a little bit lower strength and approximately 1.4 times greater elongation as compared with the strength and elasticity of Ti-6Al-4V alloy on tensile tests. Microstructure of the Ti-6Al-7Nb alloy exhibited a refined two-phase structure consising of an acicular alpha phase in prior-beta grains. It is considered that the strength of the of the alloy is due to this refined structure. From these results, it was concluded the alloy would be useful in conventional dental casting technique for titanium alloys.

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Gold-Silver-Palladium alloy is generally considered softened by rapid heating or cooling such as by laser irradiation. We therefore investigated the hardening mechanism for base materials of Gold-Silver-Palladium alloy, Ag-Pd-Cu alloy and Ag-Pd-Cu-Zn alloy, which do not contain gold, using laser irradiation, and obtained the following results.
1) The surface hardness of 45 wt% Ag-25Pd-30Cu alloy, among the Ag-Pd-Cu alloys, was 264.0 HV after laser irradiation, 66.8% harder than that after casting. Based on the results of X-ray diffraction, the hardening mechanism of the alloy by laser irradiation was a phase transformation from α₂ (Ag-rich) to α₁ (Cu-rich).
2) The surface hardness of 36.0 wt% Ag-31.5Pd-22.5Cu-10.0Zn alloy, among Ag-Pd-Cu-Zn alloys, was 334.5 HV after laser irradiation, 70.9% harder than that after casting. EPMA at the site hardened by laser irradiation and the same site after additional heating in stain-free electric furnace, revealed a great difference between atomic distributions at the two sites. The hardening mechanism of the alloy by irradiation was found to be strain induced by changing solid solution limits.

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Sliding frictional wear of 5 dental restorative materials, including composite resin, was investigated using a new sliding frictional wear testing instrument and the wear mechanism between composite resin and other materials was discussed. Ag-Pd-Au alloy, Ni-Cr alloy and porcelain in addition to two composite resins were prepared as the wear test specimens. Furthermore, two types of heat-curing composite resins were used as the opposing material of the wear test specimen. These composite resins were made from Bis・GMA-Tri・EDMA mixed monomer and silanized conventional filler (1.9 and 4.8μm average particle size). The filler content was 60 wt% of the specimen. All test specimens of other materials, except composite resin, were made by the methods recommended by manufacturer.
From the results of the wear test, it was suggested that the wear behavior between composite resin and various dental restorative materials was influenced by the size of filler particles in the composite. When filler particle size was large, the wear resistance of the composite resin increased markedly. Ag-Pd-Au alloy, Ni-Cr alloy and porcelain showed more wear resistance when opposed to composite resin with large filler particles.

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Shear bond strength to dentin was measured using the jig proposed by L.G. Watanabe. 4% 4-META/MMA-TBB, 3% HNPM/MMA-TBB, and 5% Phenyl-P/MMA-TBB resins were applied to extracted bovine dentin conditioned with 10-3 solution for 10 seconds. The shear bond strengths of the tested resins were 28.1 MPa, 12.3 MPa, and 24.5 MPa, respectively. Fracture due to shear stress occurred at the demineralized dentin but not in areas fully impregnated with resin in all three bonding systems. The demineralized dentin not fully impregnated with resin could be recognized as a defect in the bonded dentin samples after soaking in water for one day. It was difficult to find such defects in bonded speciments using tensile bond strength measurement. Shear bond test is a more suitable method than tensile test to detect defects in specimens of resins bonded to extracted bovine dentin.

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This investigation studied methods of increasing toughness and lowering the melting temperature in 12 mass% Au-20mass% Pd-Ag-Cu alloy. This study also examined the influence of adding 2 mass% Zinc to alloy system.
To this end, the copper content of the 12 mass% Au-20 mass% Pd-Ag-Cu system alloy was increased to the eutectic line of the Ag-Pd-Cu ternary phase diagram.
This experimental alloy showed a balance between tensile strength and elongation at all heat treating temperatures. The tensile strength and elongation were approximately 940 MPa and 22% by age-hardening, 880 MPa and a minimum of 22% by solution hardening, and 680 MPa and 44.4% by air cooling.
Hence by increasing the copper content, the toughness of this alloy system can be improved.

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Using mercuric chloride, we examined the in vitro resistance of HaLa cells to mercury. Several modes of cell treatment were studied, including a 6-hour treatment followed by either 24 or 96 hours of cultivation in fresh medium as a recovery phase. The above combination was also repeated up to three times. Resistance occurred after exposure to the chemical at a level greater than 5μM, and also in treatments without cell recovery or with 24-hour recovery phases. The resistance of cells to mercuric chloride might reflect cellular changes induced by the noxious substance. This possibility should be considered in biomaterial testing when elucidating the physiological role of the cells.

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