The polymerization and thermal contractions of 39 products of non-aqueous elastomeric impression material recently available were directly measured by a non-pressure method.
　The polymerization contraction of each material generally agreed with the theory of polymerization reaction of the materials. The tendency of polymerization and thermal contractions depended upon the products in regular and injection types, while the contractions of putty type were less than those of the other types.
　The results indicated that the thermal contraction of elastomer was an important factor affecting the accuracy of the stone-die, since a large amount of the thermal contraction was found compared with the polymerization contraction.

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　The total contraction of syringe-type elastomeric impression materials polymerized at oral temperature was directly measured by a non-pressure method. Then the effects of the thickness of putty and syringe materials to the total contraction of a silicone laminate impression were determined.
　In general, each material contracted in accordance with the sum of polymerization and thermal contractions individually measured. Some products demonstrated less contraction in water than in air.
　The silicone laminate impression showed an alternative contraction according to the rate of thickness of putty and syringe materials. The increase in the syringe/putty ratio resulted in greater contraction of the laminate impression with a given thickness of putty material.

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　The effects of grain size on sintering process of powder compacts and bending strength of sintered bodies were investigated in the porcelain bodies consisting of low fusing glass powder and crystal powder. The glass and alumina powders were sifted through screens using a sound wave sifter. The porcelain bodies were blended glass powder and alumina powder of various grain sizes at a weight ratio of 1 to 1.
　The glass powder compacts or mixed powder compacts of glass and alumina were densely sintered at a low temperature with a decrease in the grain size of the powder. Bending strength of sintered bodies increased with a decrease in the grain size of the powder, and was inversely proportional to the square root of the grain size. The mixed powders were more affected by grain size in sintering process of compacts and bending strength of sintered bodies than were the glass powders.
　The experimental results on effects of glass or alumina grain size on sintering process and strength of mixed samples were clearly affected by the grain size distribution of glass powder. Grain size distribution of alumina powder had little or no effect on the sintering process of mixed compacts or the strength of sintered composite bodies.

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　I examined the effects of EDTA・Fe・Na on adhesion to bovine dentin with 4-META/MMA-TBB resins. The effect of glutaraldehyde on the pretreatment for the bonding was also studied. There were optimal 4-META concentrations in the bond strength to the each pretreated ground dentin.
　Pretreatment of ground dentin with 0.3 M EDTA・2Na-0.2 M EDTA・Fe・Na (EDTA 3-2) at pH7.4 for 60 sec, and the combined pretreatment with 5% glutaraldehyde ethanol solution (GA EtOH) after EDTA treatment improved bonding of 4-META/MMA-TBB resins to dentin.
　The maximum tensile bond strength, 23 MPa, was obtained with 1% 4-META/MMA-TBB resin to EDTA 3-2 treated dentin, and 24 MPa with 7.5% 4-META to 0.5 M EDTA treated dentin when 5% GA EtOH applied for 30 min before bonding.
　The samples, treated with EDTA 3-2, 5% GA EtOH for 60 sec, and then bonded with 5% 4-META/MMA-TBB resin, showed the most stable tensile bond strength up to 4 weeks of immersion in water at 37℃.
　SEM observation showed that the formed hybrid layer of the dentin and the resin was the most insoluble with 6 N HCl when treated with EDTA 3-2 and 5% GA EtOH prior to the bonding.
　These results indicated that pretreatment with EDTA 3-2 and 5% GA EtOH is effective for obtaining a good bond to dentin. It is assumed that Fe³⁺ in EDTA 3-2 changes the amount of water bound to non-collagenous dentin proteins. Glutaraldehyde crosslinks collagen. These effects improve the interpenetration of monomers into the dentin. 4-META also promotes monomer interpenetration into the treated dentin. A stable bond between the dentin and 4-META/MMA-TBB resins occurrs by the polymerization of diffused monomers in situ.

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　Recently base metal alloys such as Co-Cr alloys and Ni-Cr alloys are used frequently in dentistry. However, it is difficult to work them precisely by the conventional dental casting method and the conventional machining. Therefore an electric discharge machining was introduced to make dental prosthetics without failures of precision and mechanical properties of these alloys. In this study the electric discharge machining properties of 4 dental alloys were investigated and some applications for the dental prosthetic works were performed.
　Each alloys had a suitable current condition. Ag-In alloy had the highest machining speed among the alloys tested. Co-Cr and Ni-Cr alloys had machining properties similar to Ag-Pd-Au alloy. Generally, small electrode elimination, high surface roughness and wide clearance between the electrode and the metal were obtained by electric conditions that showed high machining speed.
　Pulse on time, pulse off time and the duty factor had to be controlled properly to obtain stable machining.
　Electric discharge machining could be applied to work the complicated shape of grooves and holes on dental prosthetics precisely without the influence of heat or vibration.

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The adhesive durability of posterior composite resins under repeated compreissve loads was investigated. Four types of cavities, i.e. box, box with bevel, saucer, saucer with bevel were prepared and filled with composite resins. Two filling procedures were examined, one was the conventional method in which filling was done at one time, while in the other method, filling was completed in two steps. Specimens were subjected to repeated compressive loads, and the adhesive durability was evaluated by the dye penetration test. It was found that the marginal leakages were promoted by repeated loadings. The saucer cavity showed less marginal leakage than box cavity, and bevel had excellent effects on the improvement of the durability of both types of cavities. The filling procedure has little effect on the durabilitiy, and specimens filled by the two-step method show poorer durability than specimens filled by the conventional one-step method.

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　A new dental cement was developed by the use of tetracalcium diphosphate monoxide, Ca₄(PO₄)₂O and dicalcium phosphate dihydrate, CaHPO₄・2H₂O. When an equimolar mixture of the two calcium phosphates was mixed with diluted phosphoric acid, it hardened into dental cement consisting of a phase of hydroxyapatite, which is the main inorganic constituent of hard tissues. During the spatulation, the pH of the paste rapidly increased to the neutral range and the setting reaction proceeded in weak an alkaline range. In this regard, this cement is expected to be the least irritating of any dental cements presently available. As a result, this cement is useful as tempoary fillings and as root canal fillings.
　The presence of synthetic hydroxyapatite and/or fluoridated hydroxyapatite reduced the setting time. This finding suggests that microcrystals of hydroxyapatite present on the surface of any hard tissues serve as nuclei for subsequent apatite crystal growth. Comparison of the cements stored in artificial saliva for short and long period suggests that remineralization occurs during the storage, resulting in improvement of cystallinity and mechanical properties such as wet compressive strength.

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　As methods to reline ill-fitting dentures, there exists a direct method with cold-curing resin, and an indirect method with heat-curing resin. However, both methods are not necessarily satisfactory in practice, because the former causes the irritation to the soft tissue especially by the monomer, and the latter causes the deformation of the denture base during the processing procedure.
　"Eporex-R" is the light cured direct relining material which has been developed, aiming to resolve problems which conventional relining materials possess as mentioned above.
　This material had already been investigated on the physical and chemical properties, and the biological safety, and proved to be a quite effective relining material clinically. In this article, it was discussed to what extent the somewhat brittle nature of this material is reinforced by the denture base resin. In addition, the fitness of the denture relined by this material was compared with those of other materials.
　As a result, "Eporex-R" proved to be much better than conventional heat-curing resin, and comparable to conventional cold-curing resin, in fitness. As for reinforcing effect, laminating of the denture base and the new material increased the plastic deflection and thus its toughness. The result suggests that the denture relined by "Eporex-R" eliminates brittleness possessed by conventional denture base materials, and increases the durability of the denture.

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　The purpose of this study was to investigate the effects of the addition of third elements to 70% Co-30% Pd alloy on mechanical properties, microstructures, thermal expansions, bonding strengths and bonding mechanism.
　(70% Co-30% Pd)-6%〜20% Ti alloys had higher bonding strengths than (70% Co-30% Pd)-Au or Pt alloys. Especially, (70% Co-30% Pd) 90%-10% Ti showed bonding strength greater than those of alloys on the market. However, the addition of more titanium to 70% Co-30% Pd alloy made decreased the elongation and increased the hardness.

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Corrosion resistance in Ti-Ni shape memory alloys in 1% NaCl solution was studied by means of anodic polarization measurement. To improve the biocompatibility of Ti-Ni for implant material, surface coating such as TiN, TiCN and oxide film were applied and the corrosion resistance and shape memory effect were studied. By coating, the amount of current density decreased, and at 2, 000 mV, it was 1/100 to 1/1000 times that observed in Ti-Ni without coating. No abrupt current increase by pitting corrosion was observed. Shape memory effect of coated specimens by bending deformation was observed. Before coating, Ti-Ni recovered between at 20° to 43℃. In TiN coated and oxide film coated specimens, recovery temperatures were elevated about 15° and 27℃ respectively. However, in TiCN coated specimens, the film pealed when the specimen was bent. Anodic polarization measurement was carried out by using the specimen shape recovered. In both TiN and oxide film coated specimens, current densites on the compression strain side were larger than those were obtained in the specimens as coated, but the current densities on tension strain side were smaller. On the compression side in TiN coated specimens, surface cracking occurred by bending and pitting corrosion was observed after polarization. The results suggest that thinner coating film of TiN or pure Ti metal coating film which deform plastically will be required.

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　Shear stress vs shear rate curves and shear stress vs time curves of experimental agar impression materials were determined with a cone-plate type rheometer ranging from about gelation temperature to 60℃. From these curves, the rheological properties were estimated by measuring the flow characteristics, the apparent viscosities, the yield values and the areas of hysteresis loop. The effects of agar concentration and additives on the rheological properties of experimental agar impression materials were also investigated.
　The binary agar-water samples were made with agar concentration as follows : 4, 6, 8, 10, 12, 14, 16 wt%. The flow characteristics of these samples were thixotropy and pseudo-plastic, which changed with agar concentration and measuring temperature.
　The apparent viscosities, the yield values and the areas of hysteresis loop of the samples increased with decreasing temperature and increasing agar concentration. The apparent viscosities showed the Andrade type viscosity change.
　The ternary agar-water-additive samples were made with five additives (zinc oxide, iron oxide, potassium sulfate, sodium borate and glycelin) into 10 wt% agar.
　The apparent viscosities, the yield values and the areas of hysteresis loop of the samples increased with increasing amounts of zinc oxide, potassium sulfate and sodium borate, whereas these properties decreased with increasing amounts of iron oxide and glycelin.

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