At the beginning of fundamental studies on stone cast deformation by means of a three dimensional measuring system, the standard model having a standardized coordinate settlement out of stone cast was divised. An alginate indirect model was made of stone. Dimensions were measured by means of the three dimensional measuring system, and profiles also were measured in accordance with the profile measure program. No definit deformation was observed on the stone cast. The result indicated that the standard model would be available for the further study.

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The quantification of impression pressure has been experimented through the observation of the force appearing during impression. The impression pressure was quantified by the final force appearing during impression. Then two alginate impression materials were measured.And the influence of the four factors (type of tray, quantity of powder, mixing time, press speed) was examined employing a L₁₆ (2¹⁵) table of orthogonal array based on design of experiment. The results were statistically analyzed. The impression pressure was successfully quantified. The different characteristics of the products employed were revealed. The quantity of powder and the mixing time effects were not significant. Type of tray effect was highly significant. The press speed effect was significant on the case of using closed type tray.

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The effect of In and/or Sn additives to 50Au-25Pd-15Ag-5Pt alloy on the mechanical properties was investigated. Either 0.25, 0.75, 2.25, 6.75 or 10.00wt% of In or Sn wasadded to the mother alloy and 10 alloys were prepared. Another 16 alloys were made by the addition of both In and Sn. For these alloys, the weight percentage of In was either 0.5, 1.5, 2.5 or 3.5 and so was that of Sn. The tensile strength, the elongation and the Vickers hardness were measured for each alloy and the pull through shear test was performed to evaluate the bond strength between the alloy and the porcelain. The obtained data were statistically analyzed. In addition to the above tests, the surface texture was observed under SEM and the distribution of the metal elements was analyzed using XMA. These investigations were performed for each alloy after heating to the degassing temperature and to the firing temperature. The results are summarized as follows. In the case of the individual of addition In or Sn, the minimum additive amount is estimated to be 6±0.5wt% for In and 4-6wt% for Sn in order to obtain the suitable mechanical properties including the bond strength. On the other hand, when In and Sn are added together, the optimum additive amounts are 0.5wt% In and more than 3.3wt% Sn, 1.5wt% In and more than 2.8wt% Sn or 2.5wt% In and more than 2.2wt% Sn.

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Solidification mechanism relating to fully equiaxed castngs of Ni-Cr alloy in dental-centrifugal casting process was qualitatively discussed. The subsequent results were obtained by performance of some experiments. Crystal grains locating at direction of centrifugal force in ingot after solidification were finer, they being just below sprue were fine with enlarging its diameter, they accumulated on the ledge setting in the mold cavity, and so forth. These results may be caused by which mechanical or thermal convection makes crystals separate from mold wall and then centrifugal force makes them move among the liquid and accumulate on the bottom. In particular, accumulation and packing of crystal grains make alloy in or near sprue solidificate. The discussion of the present paper may point out a number of unresolved areas which should stimulate future work.

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1, 3-Bis (methacryloyloxyethyloxy) benzene (RDMA) was prepared to improve the mechanical properties of dental composite resins. We could polymerize more readily at room temperature with chemical and photo initiations than widely used Bis-GMA or TEGDMA. Amounts of monomer eluted from resin made with RDMA was lower than those made with Bis-GMA. It is excellent in hydrophobicity. Combination of mixtures of RDMA and TEGDMA with TMPT filler, which is an reactive organic composite filler, improved the mechanical properties of composite resin such as hardness, compressive strength and amount of uptaken water.

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Elastomeric impression materials undergo the setting reaction to form polymer network succeeding gelation. The progress in setting reaction of the material and the ensuing change in their dynamic mechanical properties were followed by calorymetric measurements and by dynamic shear measurements, respectively, under the same condition with each other. Correlations between the changes in dynamic mechanical properties and the extent of their reaction revealed the network forming process of the material, closely related to the functionality of the prepolymer and/or crosslinking agent in the material. Polyether material containing the prepolymer with higher functionality has a gel point at earlier stages of the reaction, whereas polysulfide material containing the prepolymer with lower functionality has a gel point at later stages of the propagation reaction.

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Cyanoacrylate, which has extremely fast setting time but may be weak for water immersion and impact force, was studied. The tooth surface, stainless steel and acrylic resin were selected for adherend, and the stability of adhesion between them was examined. Parcolation test showed that cyanoacrylate was stable with acrylic resin, but very unstable with stainless steel. The tensile strength decreased with the increase of crosshead speed. The impact strength of cyanoacrylate, which was measured by the modified Izod method, was low in comparison with other orthodontic adhesives. The effect on adhesive strength of cyanoacrylate by the use of acidic solution containing fluoride as a surface treatment agent was examined, and its strength increased at low fluoride concentration (1% NH₄F, NaF). These results suggest that cyanoacrylate has some possibility of its application for orthodontic treatment under a considered suitable condition of adherend surface.

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