This study investigated the effect of long-term storage on the stability of tetracalcium phosphate powder. Tetracalcium phosphate powder was prepared as an equimolor mixture of calcium hydrogenphosphate dihydrate and calcium carbonate heated at 1400℃ for 2 hours and then cooled in air. The shape of tetracalcium phosphate powder was observed by scanning electron microscope (SEM). A crystalline variations of tetracalcium phosphate powder were investigated by x-ray diffraction analysis using an automated deffractometer (RAD-C, Rigaku Inc.) with scan range from 25° to 40°(2θ). Differential thermal analyses of tetracalcium phosphate powder were also performed using a differential thermal balance (TG-DTA, Rigaku Inc.) with scan rate of 10℃ per min, and scan range from room temperature to 1000℃. The tetracalcium phosphate powders were stored at room temperature (25±2℃, 55±5% r.h.) and at 37℃ with a relative humidity of 95±5%. The storage periods of tetracalcium phosphate powder were 1 hour, 3 hours, 6 hours, 1 day, 3 days and each week from 1 week to 10 weeks after being fired.
The shape of tetracalcium phosphate powder observed by SEM did not show any change with increases in the storage periods under both environmental conditions. Crystalline variations of tetracalcium phosphate powder did not show any change on x-ray diffraction analysis as storage periods increased under both environmental conditions. The weight of tetracalcium phosphate powder stored at 37℃ and a relative humidity of 95±5% decreased with increasing temperature up to 420℃.
The results suggested that the surface of tetracalcium phosphate powder adsored water at 37℃ and a relative humidity of 95±5%.

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Chitosan is absorbed in vivo. Chitosan sol is produced by dissolving chitosan in a solution of malic acid and malonic acid. A chitosan film is formed by mixing this sol with apatite materials, followed by neutralizing with a 5% sodium polyphosphate solution, then gelatinized. In the present study, we examined the relationship between the amount of added chitosan and shrinkage, hardness, tensile strength and elongation.
The following results were obtained. : The chitosan sol which was dissolved with malic acid exhibited the largest amount of shrinkage at the neutralization process. The chitosan sol dissolved with malonic acid showed the largest amount of shrinkage during the drying stage. By increasing the amount of chitosan, the shrinkage increased during the neutralization process, but there were no significant changes during the drying stage. Increasing the amount of chitosan resulted in increased hardness. The hardness value of dried chitosan was higher than that of neutralized chitosan. By increasing the chitosan, the tensile strength increased. It was also observed that elongation of the dried chitosan film increased.

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Bone filling materials must be absorbed in vivo to promote the osteogenesis. It is also necessary for the original strength of the bone filling materials to be reduced after they are filled into the bone, in order to help cells and blood vessels penetrate these materials.
In this study, chitosan films which were soaked in 37℃ physiological salt solution were investigated for changes in tensile strength and elongation as a function of time, changes in the surface were also observed.
The following results were obtained: After soaking the chitosan film in 37℃ physiological salt solution for 2 weeks, tensile strength and elongation decreased. By increasing the amount of chitosan, it was found that there was less reduction in tensile strength of the chitosan film even after 2 weeks of soaking in physiological salt solution. By increasing the amount of chitosan, it was found that there was less reduction in a hole in the surface of chitosan film even after 2 weeks of soaking in physiological salt solution. The tensile strength of chitosan film prepared with malic acid showed a greater reduction than that of chitosan film prepared with malonic acid. After soaking in 37℃ physiololgical salt solution for 1 week, chitosan (0.5 g and 0.6 g) film prepared with malic acid showed greater elongation than that after soaking for 1 day and 2 weeks. After soaking for 1 week, chitosan (0.5 g) film prepared with malonic acid showed greater elongation than that after soaking for 1 day and 2 weeks.

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To elucidate the effect of dental materials on oral mucous membrane, an attempt was made to examine cytotoxicity of 3 types of denture base resins and 2 types of resin monomers utilizing commercially an available tissue model, TEST SKIN ^2TM. It was found that heat and microwave curing resins did not show cytotoxicity, as indicated in previous reports. However, self curing resins and monomers MMA and TEGDMA showed strong cytotoxicity, which contradicted previous reports. It seemed that the mode of specimen contact with the cells contributed to the results. It was also noted that further improvement was needed for efficient use in cytotoxicity testing of dental materials.

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In this study, radiopaque composite resins were prepared. These composite resins contained complex filler with SiO₂ (70 wt%) filler and ZrO₂ (30 wt%) filler treated its surface with γ-methacryloxypropyl-trimethoxysilane. Their radiopacities and physical properties were evaluated for clinical use.
Radiopacity, knoop hardness and compressive strengths were superior to those of commercially available composite resin core materials. Regarding other physical properties, the diference was not significant.
We suggest that these radiopaque composite resins would more effectively obtain high radiopacity without decreasing physical properties, and may have good physical properties for clinical use.

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Rolled 30Pd-15Cu-55Ag (AP) and 12Au-20Pd-15Cu-53Ag (APG) alloys were prepared and 600 mass ppm of Ti, V, Cr, Mn, Zr, Nb, Ru, Rh, Hf, Re, Os and Ir was individually inoculated into the AP and APG alloys. These alloys were melted by high frequency induction heating, and solidified with slow cooling at a velocity of approximately 6℃/s. After 800℃×30 min soaking, these alloys were quenched in water of room temperature. The crystal grain of the alloy specimens was observed with an optical microscope.
Under the same solidification conditions, the mean grain size (grain diameter) of AP and APG mother alloys, were 0.3〜1.3 mm (mean value: 0.8 mm). By inoculating 600 ppm Ir, Ru, Os, V and Re into AP and APG alloys, the mean grain size of the alloys was refined to approximately 60〜221 μm.

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Experimental 30Pd-15Cu-54Ag and 12Au-20Pd-15Cu-52Ag alloys containing 1% zinc as a deoxidizer (APZ and APGZ) were prepared and a minimal mass of iridium, ruthenium and osmium determined by preliminary investigation, was independently inoculated into APZ and APGZ alloys. Using dental precision casting technique, cast specimens were made from these alloys and both mechanical properties and grain size of the the alloys were measured. Most of the mechanical properties of APGZ series were improved by inoculation with 200ppm Ir, 300 ppm Ru and 200 ppm Os. After softening heat treatment, tensile strength and elongation had a highly significant correlation with grain size, and significantly increased as the grain size decreased.

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This study investigated the characteristics of various types of non-asbestos casting ring liners. SEM observation, rate of vacant space and water sorption of the non-asbestos ring liners were examined. Fifteen non-asbestos casting ring liners and three asbestos ribbons were used. The main fibers in the liners were round rod-like fibers in A〜D groups and irregular form in the E group with/without globular particle and powder. The liners of A group (the rock-wool type) showed a higher rate of vacant space and higher water sorption, those of B〜D group (the ceramic fiber type) except for NA14 showed a higher rate of vacant space and lower water sorption and those of the E group (kaolin type) showed a lower rate of vacant space and lower water sorption compared with asbestos ribbons. NA14 (Ribbon Wool) of D group showed the highest rate of vacant space and especially a higher water sorption.

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This study investigated some properties of reinforced glass ionomer cement and compared them with conventional glass ionomer cement for luting. Reinforced glass ionomer cement (Fuji DUET) and conventional type (Fuji I) were used in this study. Each cement powder was mixed liquid following the manufacturer's recommended ratio. The consistency, setting time (37℃, 95±5% r.h.), film thickness, compressive strength (24 h), solubility and disintegration (24h) of these cements were measured by the methods specified by ADAS No. 8 for zinc phosphate cement. Also, the working time of these cements was determined. The tensile bond strengths and wettabilities of reinforced and conventional glass ionomer cements bonded to each substance were measured according to methods previously described.
The consistency, setting time, working time, compressive strength of reinforced glass ionomer cement were significantly smaller than those of the conventional type. The film thickness, solubility and disintegration of reinforced glass ionomer cement were similar to those of conventional ionomer. The wettabilities of reinforced glass ionomer cement to each substance except for titanium showed significantly larger values than those of conventional ionomer. The tensile bond strengths of reinforced glass ionomer cement to each substance except for Au-Ag-Cu alloy were similar to those of conventional ionomer.
The results suggested that the reinforced glass ionomer cement did not have any properties that were more difficult to work with compared to conventional glass ionomer cement for luting even though the consistency, working time, compressive strength of reinforce glass ionomer cement were significantly less than those of conventional type.

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Reaction layer structures of titanium cast in three molds containing spinel (MgO・Al₂O₃) were investigated and compared by microstructure observation, electron probe microanalysis and measuring hardness. The molds were made from a spinel powder and two commercial investments, in which alumina and magnesia were involved and reacted to form spinel by heating. For the spinel mold, the reaction zone consisted of a baked product layer and the α case which was divided into two layers. Whereas the outside was stabilized and hardened by solid solution of Al, the inside was not so much hardened without a solid solution of Al. For the phosphate bonded investment, Al diffused deeply into the casting, the P-rich phase with a net-like structure extended more deeply, but the Al-stabilized α case was not formed. For the investment mixed with magnesium acetate solution, the Al-stabilized α case with higher hardness value formed on limited surfaces. On most surfaces, however, the acicular crystal structure was exposed without such a hard casing. For these investments, components other than spinel influenced the reaction layer structure.

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Experimental soft lining materials were produced using poly Ethyl methacrylate (PEMA), poly n-Butyl methacrylate (PnBMA) or poly iso-Butyl methacrylate (PiBMA) powders and liquid plasticizers added Ethyl methacrylate (EMA) or Butyl methacrylate (BMA) monomer. The powders and liquids were mixed for 30 sec and then mixtures were light-cured after 24 hrs from the start of mixing. This investigation examined the effect of differences in kinds and mixing ratios of monomers and plasticizers to improve the durability of acrylic soft lining materials. We used a viscometer to evaluate apparent viscosity, a pulsating rheometer for elastic recovery and experimental hardness tester for hardness and stress relaxation. As a result, compositions that are applicable as soft lining materials were less than 30% EMA with PEMA-DBP type, less than 20% EMA with PEMA-BPBG type and less than 10% BMA with PiBMA-DBP and PiBMA-BPBG type.

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Temperature fluctuation at an interface between the retainers of adhesion fixed partial denture and the resin luting agent was investigated when hot green tea (60℃ to 75℃) and ice cream (-12℃) was consumed. Au-Ag-Pd alloy (12% Au) was cast to form retainers for adhesion fixed partial denture for the lower and upper central incisor and first molar. A copper-constantan thermocouple with a diameter of 0.13 mm was soldered to adhesion surface of the retainers. Then retainers were adhered to the tooth surfaces of ten patients using 4-META/MMA-TBB resin. Measurements were obtained at 8 points in each patient. The temperature ranged from 10.5℃ to 56.5℃ at the interface of the lingual and palatal surface and from 25.6℃ to 47.4℃ at the labial and buccal surface. The lowest average temperature of 10.5℃ was observed at an interface of the palatal surface of the upper central incisor and the highest of 56.5℃ was at lingual surface of the lower central incisor.

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This study was concerned with the development of metal primer for crown and bridge resin. Nine kinds of adhesive cyclophosphazene monomer were synthesized and analyzed by IR and ¹H-NMR. Then, 20〜50wt% of synthesized monomers were mixed with commercial monomers and light-cured metal primers were produced by adding photosensitizer. As an adherent, cobalt-chromium alloy measuring 3 mm in diameter was prepared. Tensile adhesive strength was measured after immersion in water at 37℃ for 24-hour.
On IR and ¹H-NMR, all synthesized monomers were within expectations.
Among these, the synthesized monomer with the greatest adhesive strength was P₄N₄[OOCC₆H₃(COOH)₂]₃[OCH₂CH₂OCOC(CH₃)=CH₂]₅ replacing 3 mols of Cl with 1, 2, 4-benzene tricarboxylic unhydrate and 5 mols of Cl with HEMA. When 40 wt% this synthesized monomer, 40 wt% HEMA and 20 wt% U-2TH were mixed, tensile adhesive strength was 22.9 MPa.

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This study investigated the relationship between fluorine (F) release from glass-ionomer cement (GIC) and disintegration of the cement.
Two kinds of GIC products were used. Immersion in distilled water began, 5 or 60 minutes after the start of mixing. After immersion for two weeks, both the glass particles and the cement matrix area in the disintegrated surface of GIC were analyzed by electron probe microanalyser to determine the amount of elements (F, Al, Si, Ca and P) lost. All elements in the cement matrix were reduced, however, the propotion of glass particles did not change. The reduction of F in the cement matrix immersed 5 minutes after mixing was 72.4〜73.3%. Those of other elements ranged from 7.7〜37.5%. Although the loss of F at 60 minutes was almost the same as that at 5 minutes, those of other elements decreased to 0〜22.3% as the start of immersion was delayed.
The results demonstrated that F released from the cement matrix of GIC during the initial disintegration and the rate of F lost from the matrix was high, compared with those of other elements.

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