It has previously been reported by the authors that the impression pressure was quantified as the final force occurring during impression. In this study, the influence of the type of tray on the impression pressure of twelve alginate materials was investigated. Further, the relationship between consistency of an alginate mix and the impression pressure was examined.
The impression pressure decreased with increases in the opened area of the tray. The decreasing rate of the pressure depended on the materials used. There was an inverse correlation between the consistency and the impression pressure, but the correlation coefficient differed with the type of tray apparently due to the effect of the characteristics of the materials.

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Accurate grasp of dimensional accuracy and deformation of stone cast, which is considered difficult by conventional methods, was attempted by means of a three-dimensional measuring system. In the present study, a standard model in the system having a standardized settlement out of stone cast was used. The effects of the type of mold (straight, tapered and undercut) and the various impression materials (alginate, polysulfide and silicone) were investigated.
With respect to the straight and tapered types with all impression materials, no deformations were observed, but with respect to the undercut type, deformations attributable to different impression materials were observed on the side faces of the stone cast. This measuring method appears to be appropriate for measuring dimensional accuracy and deformation of stone cast.

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Bending, tensile and izod impact strength, and transversedeflection values were examined on composite specimens of treated kevlar fiber (KF) cloths sandwiched by PMMA resins. The strength of the composites, especially the izod impact strength, were twice as high as those of the CF-PMMA composites.
Derivatives of poly(p-phenylene terephthalamide) (PPTA) molecules were also examined as rigid core components instead of KF cloths. The composites are termed molecular composites.
N-substituted PPTA, such as the N-alkylated type, were prepared from metalated PPTA via metalation using sodium methylsulfinylcarbanion and the corresponding alky-halides in dimethyl sulfoxide.
The reinforcement with the rigid molecules increased compressive, diametral and bending strengths of the molecular composites by ten〜fifteen percent from the original resins.

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The present study analyzed the chemical adhesive phenomenon during casting between phosphate bonded investment components and surface oxides on non-precious dental casting alloys, e.g., Co-Cr alloys. Solid state reactions of MgO-Cr₂O₃ and NH₄MgPO₄・6H₂O-Cr₂O₃ mixtures were analyzed by thermal analysis [thermogravimetric analysis (TG) & differential thermal analysis (DTA)] and the reaction products were identified by X-ray powder diffraction analysis.
Pichromite (MgCr₂O₄), which give rise to the chemical adhesive phenomenon, was formed in MgO-Cr₂O₃ in the temperature range of 610〜640℃, however, it was not formed in NH₄MgPO₄・6H₂O-Cr₂O₃ below 1200℃. Magnesium pyrophosphate (Mg₂P₂O₇), one of decomposition products of NH₄MgPO₄・6H₂O, was converted from an amorphous to crystalline state at nearly 695℃.

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Internal stress of heat-curing resin and self-curing resin during polymerization was investigated. In addition, internal stress of the cured resins during heating to 120℃ and then cooling to room temperature was investigated.
The compressive stress developed during heat-curing resin and the self-curing resins polymerized at 23℃ and 50℃ were 176 kgf/cm², 251 kgf/cm² and 338 kgf/cm², respectively, after the termination of polymerization. When the cured resins were heated to 120℃, the compressive stress in the heat-curing resin and self-curing resin became 0 kgf/cm² at about 120℃ and 60℃, respectively.

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For accurate reproduction of the physical properties, surface texture and gloss can be obtained by porcelain firing, the muffle of the porcelain furnace is required to accurately control the firing temperature.
We examined the muffle of the porcelain furnace. The mufflle of the porcelain furnace was controlled by a computer to verify the working temperature.

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The cross-section of high copper amalgam filled in epoxy tooth die was observed by a new type EPMA (CMA: Computer-aided Micro Analyzer or Comprehensive Multi Analyzer) that provides rapid analysis of a wide area (max. 80 mm×80 mm). Quantitative are analysis of Hg, Ag, Sn and Cu throughout the specimen was carried out in one process. This method has been difficult by conventional EPMA.
The intergration of a specific element was not found in any region of specimen. This CMA may be useful for analysis of dental materials.

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Changes in impact sound given with a mallet at a crown during cementation were recorded and the electrical contact between a crown and an abutment were also recorded simultaneously. Abutments were lathed with brass, frustum of a cone form and the weight was about 8 g. Crowns were cast with K-metal and were about 3 g in weight.
The tone of the impact sound changed during cementation. In early stage, the main vibrator was the crown, but in latter period, the main vibrator was the abutment and supporting apparatus.
The absence of change in tone of the impact sound indicated that the cementation of the cast crown was incomplete.
The direct contact between the crown and the abutment does not always bring the change in tone of the impact sound.
Judging from the electrical and dimensional measurements between the crown and the abutment, it seemed that the cementation of the cast crown is frequently imcomplete when the powder-liquid ratio of the cement was thicker than 1.3 g/0.5 ml.

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We measured the adhesive strength in all combination of 5 brands of bonding agents and 5 brands of composite resins, and also investigated the adhesion tendency to the cements that are used as cavity lining material.
Bonding agents that contain phosphate phenyl ester as a monomer, have high adhesive strength for all commercial composite resins with Bis-GMA as the main component.
The adhesive tendency of bonding agents for human enamel was relatively strong compared to dentine in most cases. Also, etching by phosphoric acid had a marked effect on the adhesion to enamel, but the effect was not observed with dentine.
The adhesion to the zinc-polycarboxylate cement, while with zinc-oxide phosphate cement and glass polyalkinoate cement, the adhesive strength was relatively weak, and the values differed according to the kinds of bonding agent. However, it was stronger than the adhesive strength between the cement and dentine.
Zinc-oxide eugenol cement interfered with the setting reaction of the bonding agent.

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In this study, models of closed magnetic circuit were investigated. The Sm-Co magnet was fitted in a yoke (a cap of soft ferromagnetic materials covering the magnet, which is made of high purity high chrome stainless steel or permalloy). A disk of soft ferromagnetic stainless steel was used as a model of the root cap, and the relation between magnetic force and the size of a york was examined. To prevent corrosion of the exposed surface of the Sm-Co magnet, the surface of the magnet was covered with stainless steel or titanium foil.
The magnetic force of the closed circuit was stronger than that of the open circuit. The magnetic attractive force mainly depended on the diameter of the yoke.
Corrosion on the magnet surface was prevented by covering it with thin foil made of stainless steel or titanium using 4-META resin as an adhesive. The magnetic attractive force was 450〜630 g in this case.
As a ferromagnetic part, the disk of high purity high chrome stainless steel was used in combination with common dental casting alloys. These root caps had a satufactory ferromangnetic quality and excellent corrosion resistance.

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I examined the viscosity of the liquid component of the polycarboxylate cement. It was expected that the viscosity of the cement solution decreases when using a copolymer consisting of acrylic acid and ethylene derivatives having large side chain such as p-styrenesulfonic acid.
The measurements of IR, NMR, Mw, viscosity, and elemental analysis and thermal analysis were carried out to examine the relationship between the amount of p-styrenesulfonic acid in the synthesized copolymer with mixed amounts of acrylic acid and sodium p-styrenesulfonate, as well as its structure and properties.
The amount of p-styrenesulfonic acid in the synthesized copolymer decreased with the decrease in the mixed amounts of sodium p-styrenesulfonate. Mw of the synthesized copolymer was 2.53〜2.60×10⁵, and that of the homopolymer of acrylic acid 2.60×10⁵. The viscosity of 20 wt% solution of synthesized copolymer and that of homopolymer of acrylic acid were respectively 1.3〜8.0 and 4.6 poise. These values proved to be small, compared with those of the diluted cement solution (20 wt%) on the market.

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This study was performed to find the most effective surface treatment for obtaining the maximum adhesion between Panavia-EX, a new adhesive resin cement, and three types of dental casting alloys. The surface treatments of metals:sandblasting, EZ-Oxisor (electrical etching) and Kura-Ace (Sn-electro deposition) were used separately or in combination. Tensile bond strength of the cement to the metals after treatment was determined.
Sandblasting considerably increased the strength with Ni-Cr alloy and 20 K gold alloy, but decreased it with Au-Ag-Pd alloy. Kura-Ace extremely increased the strength with all types of alloys tested. EZ-Oxisor proved to be ineffective for improving the bond.
When the new resin cement is usid, the following procedures are recommended. The surfaces of 20 K gold alloy and Au-Ag-Pd alloy should be treated with Kura-Ace before cementing. The surface of Ni-Cr alloy must be subjected to Kura-Ace after sandblasting.

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In order to clarify the cause of the incompatibility at the interface between alginate impression and dental stone, the surface of the dental stone cast against various impressions was studied by means of measurement of surface roughness, X-ray diffraction analysis and SEM observation. Furthermore, the extracts from the gelled alginate impressions were analyzed for phosphate by use of the molybdenum blue colorimetric method.
The surface of dental stone that had much residual hemihydrate was poor. Also, some surfaces that had little residual hemihydrate were poor. In these surfaces, orientation of the dihydrate crystals was disturbed.
Formation of syngenite was not related to the degree of surface roughness. Alginate impression material with high phosphate release gave a poor surface of dental stone.

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The effects of Na₃PO₄ and Na₂SO₄ on the hydration of dental stone were examined by means of X-ray diffraction analysis, SEM observation and measurement of the setting time. The addition of very small amounts of Na₃PO₄ retarded the hydration of the dental stone and changed the morphology of the dihydrate crystals. The effect of Na₃PO₄ on the hydration of dental stone was more remarkable than that of Na₂SO₄.
The surface roughness of the dental stone cast against the agar impression, which was hydrophilic as well as alginate impression and released little phosphate, increased with increasing concentrations of Na₃PO₄ dissolved with water.
Therefore, it was concluded that one of the important causes of the poor surface of a dental stone cast against alginate impression was phosphate exuded from the impression.

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The pressures produced during edentulous impression procedures can be determined by the flow behavior of impression materials, tray modifications, and the manner in which a tray is seated. Those hydrodynamical problems were studied analytically, numerically, and experimentally with a simple model of impression taking. Compressive flow of either polysulfide liquid polymer or silicone liquid polymer between parallel disks was used as a model.
The analysis showed the same tendency with the experiments, while the calculated values were higher than the observed values. The variance is thought to be caused by the elastic effects of fluids.
The seating force and pressure were inversely proportional to 2.7〜2.8 powers of the spacing (thickness of fluids), and the distribution of pressure was parabolic; the pressure was the highest at the center and zero at the periphery.
According to the analysis, this distribution reflects that of the shear rates in the flow, and the shear rate depends upon the spacing. Thus, the geometrical conditions that affect the flow pattern in a tray, in other words, tray modifications may be an important factor in determining pressure within a tray.

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