An atomic force microscope (AFM) is good to examine substrate surface without drying of specimens. It is important to determine the monomer permeability of demineralized dentin to understand the mechanism of bonding to dentin. However, demineralized dentin is rather unstable and easily collapsed by drying. AFM observation was carried out on wet, dried and primed demineralized dentin to collect information on structural changes in comparison to the protected original surface. Ten percent phosphoric acid was used for the etchant and the aqueous 30% HEMA for primer. It was confirmed that drying of demineralized dentin induced collapse, but this could be restored by application of the primer. However, the restoration was time dependent.

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An alginate impression material, which is dimensionally stable in water, has been newly developed. The authors examined the effects of long-term immersion (three hours) of this material in the 0.1% solutions of two sodium hypochlorites and a 1,000 ppm solution of sodium dichloroisocyanurate. Dimensional changes of impressions, detail reproducibility, surface accuracy of the stone models and theree-dimensional reproducibility of edentulous models made from treated impressions were evaluated. As a result, this alginate impression material remained dimensionally stable in water and in the disinfectant solutions for three hours. Long-term immersion of the impression did not significantly affect the surface characteristics of stone models made from treated impressions. There was no deformation noted on the three-dimensionally measured edentulous models. Thus, it appears possible to be immersed for this alginate impression material in 0.1% chlorinate disinfectant solutions for up to three hours.

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The bending strength of porous hydroxyapatite sintered after compressive molding of a mixture of spherical butyl methacrylate as pore forming material and flaky hydroxyapatite prepared by hydrolysis. The effects of the mixing ratio of butyl methacrylate and the degree of compressive pressure were examined using two types of hydroxyapatite materials:calcined flaky powder and spray-dried spherical power processed by two kinds of compression methods:mold pressing and cold isostatic pressing. In the case of a low mixing ratio of butyl methacrylate or a low compressive pressure, the bending strength was not affected by the shape of the powder but decreased exponentially with increased porosity. The use of high compressive pressure on the high mixing ratio decreased the bending strength.It was suggested that the low volume elasticity of butyl methacrylate caused numerous cracks in the matrix of hydroxyapatite.

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This study evaluated the effect of mold gas permeability and casting pressure on titanium castability using an all-directional pressure-type casting machine and two different kinds of phosphate-bonded investments with different levels of gas permeability. The castability values increased with increases in the mold diameter of the higher gas permeability investment (T-invest). The influence of casting pressure on castability showed different trends, depending on mold diameter. When large mold diameters were used, casting pressure was less critical for castability. Castability was not affected by mold diameter when lower gas permeability investment (T-invest C&B), or T-invest with a sealed ring were employed. Excellent, stable castability was achieved by casting pressure over 4 kgf/cm^2.These results indicate that the influence of casting pressure on castability showed different trends, depending on the level of gas permeability in the casting mold used.

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This study developed an improved auto-mixer for double cartridge-type of silicone rubber impression materials that eliminated the necessity of strong grasping power during mixing and the lack of flux control of manual dispenser. The efficiency of this machine was evaluated. To mix double cartridge-type of silicone rubber impression materials, it was necessary for the torque of the motor to be a minimum of 67.5kg・cm (20 W motor, reduction ratio:1/7.5). The auto-mixer method was simple to operate and shortened operating time, but required a little longer working time than manual dispenser method. However there was no significant difference between these methods on same materials. Therefore, this experimental auto-mixer could improve some of the defects of manual dispensers and appeared to be available for practical application.

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This study developed a fluoride-releasing adhesive resin cement. Four kinds of liquid composites were prepared by mixing 0, 10, 20 and 30 wt% of liquid fluoride-releasing fluorophosphazene monomer with powdered aluminum silicate glass to produce a setting cement. Both fluoride release and cumulative amounts of fluoride release increased in accordance with increasing the ratio of fluoro-phosphazene monomer. Compressive strength also increased as the ratio of fluorophosphazene monomer was increased. However, tensile adhesive strength between the cement and Co-Cr alloy, Ag-Pd-Au alloy and 18 Karat gold alloy showed a tendency to decrease slightly, and both water sorption and solubility were markedly decreased.

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This study developed a new castable magnetic precious metal alloy for dental prosthetics. In this study, six kinds of precious metal alloys with Co or Fe were prepared and the melting properties, mechanical properties, magnetic forces and microstructures of these alloys were investigated. An experimental alloy (No.6) consists of 48 wt% Pd, 32 wt% Co, 14 wt% Ag, 3 wt% Au, 2 wt% Zn and l wt% In showed a melting range of 1148-1192℃, hardness of 197 Hv, tensile strength of 318 MPa, elongation of 14%, attractive force 415.0 gf and a homogeneous structure without porosity when cast.

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Commercially available pure titanium surfaces were modified using dry process including ion implantation (Ca^+, N^+, F^+), ion plating (TiN, Alumina), and the application of oxide films (titania spraying, anodic oxidation). Ion-implanted surfaces consisted of Ti compounds with the implanted elements, titanates of the implanted elements, as well as titanium oxides. Calcium titanate and Ti-F compounds were primarily formed on the Ca-implanted and F-implanted titanium surfaces, respectively. Ion-plated surfaces had compositions similar to those of theraw materials for coating. TiN-coated surfaces may be effective in improving wear and corrosion resistance. Alumina-coated surfaces showed hydrophobicity and absence of Ca-ion adsorption. Oxide films created through titania spraying and anodic oxidation treatment consisted of titanium oxides with a thickness of more than several micrometers and 300 nm, respectively. Titania-sprayed films contained a certain amount of anatase. These results indicate that surface treatment by dry process is effective on surface modifications of titanium implants.

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To understand the mechanism of casting porosity, we investigated the cavity occurring in the solidification proccss of molten titanium and Ti-6 Al-7 Nb alloy. Cavities were observed in both titanium and Ti-6 Al-7 Nb alloy, and these appeared to be backpressure porosities. The volume of the cavity in Ti-6 Al-7 Nb alloy was one third of that in titanium. The location of the cavities was in the area one third from the top surface vertically and slightly shifted from the horizontal center. The inner surface of the cavity in titanium was almost smooth except for creases, which may have been caused by martensitic transformation. As for the cavity in Ti-6 Al-7 Nb alloy, the shape was slender, and dendrite-like projections were observed on the inner surface.

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The effects of intracanal medicaments on direct tensile strength (DTS) and Micro-Vickers hardness (Hv) of bovine dentin were investigated. A dumbbell-shaped specimen was cut out from a labial dentin sheet for DTS. Bovine dentin surfaces exposed after cutting the tensile specimen sheet were used for the Hv test. The test specimens immediately after preparation were evaluated as the control. The effects of immersion into physiological saline, modified physiological saline saturating calcium and phosphorus, formocresol, calcium hydroxide paste and eugenol were examined. The DTS after eugenol immersion was significantly higher than that of the control (p<0.01). There were no significant differences between the Hv of the control and that of immersed groups. Thus, immersion into intracanal medicaments influenced the mechanical properties of bovine dentin:in particular,immersion in eugenol influenced the DTS of bovine dentin.

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The cushioning effects of waterproofed casting ring liners on the setting expansion of investment materials were evaluated by cushioning ability in 15 waterproofed ceramic liners (A:rockwool type, B:ceramic fiber low temperature type, C:ceramic fiber standard type, D:ceramic fiber low temperatures tandard type, E:kaolin type) and 3 waterproofed asbestos ribbons (AS). Setting expansion was measured using a metal mould and waterproofed liners were seated inside the sliding frame for 120 min. Cushioning effects were calculated by the difference between the setting expansion without liner and the setting expansion with liner. The cushioning effect of waterproofed liners except one product of AS increased with time. Waterproofing treatment improved cushioning effect of two products of A and one product of D, where water sorption in the dry liner was high. Waterproofing treatment changed the cushioning effect of one product of C and one product of AS for the worse. The other thirteen liners slightly changed the cushioning effect.

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