The adaptability of pure titanium cast plate dentures constructed by a DS system was investigated in comparison with that constructed by autopolymerization and two kinds of heat polymerization.
The bending proportional limit and elastic modulus of the titanium cast plate was about 68.4 kgf/mm² and 12400 kgf/mm², respectively. The titanium cast plate had a Knoop hardness number of about 250 at over the whole cross section. The discrepancy at the median line of the dentures constructed by the DS system to stone cast decreased with an increase in thickness of the titanium cast plate. The discrepancy of the dentures was correlated with the thickness of the plate. The titanium cast plate dentures, when constructed by the DS system, had a discrepancy of about 0.10 mm at the median line. However, the discrepancy of the dentures, when constructed with other polymerization methods, was about 2 or 3 times larger than that of the dentures constructed by the DS system. The discrepancy at the median line and the denture border constructed by the DS system was less than 0.10 mm after the unilateral occlusion test. However, the discrepancy of the dentures constructed by other polymerization methods was 2 or 3 times that of the dentures before the unilateral occlusion test.

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Three kinds of the polybutadiene polymethacrylates (BdPMA), with polybutadiene in the main chain, i.e., butadiene dimethacrylate (BdDMA), butadiene tetramethacrylate (BdTMA) and butadiene hexamethacrylate (BdHMA), were synthesized to obtain an extremely tough polymer. BdPMA was copolymerized with MMA and epoxy dimethacrylate (EpDMA) to form copolymer MMA/BdPMA and terpolymer MMA/EpDMA/BdPMA, and the transverse strength and the impact strength of those copolymers and terpolymers were studied.
The transverse strength and the deflection of the copolymer increased with increases in the concentration of BdPMA. The maximum values were obtained at a BdPMA concentration range of 0.3-0.5 mol%. The impact strength showed the highest value (17-20 KJ/m²) at a BdPMA concentration of 1 mol%.
The deflection of the terpolymer increased with increases in the concentration of BdPMA to 90 vol% of MMA concentration. The impact strength of the terpolymer showed the highest value (about 21 KJ/m²) at the liquid composition of 89.55 vol% MMA, 9.95 vol% EpDMA and 0.5 vol% BdTMA. As a result, extremely tough cured resin was obtained by the addition of BdPMA to MMA/EpDMA resin.

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This study evaluated the dimensional accuracy of all-ceramic crowns which were accomplished directly on the duplicating refractory die. Four commercial porcelains were evaluated. Each material was fabricated according to the manufacturer's instructions. Thereafter, the dimensional accuracy of duplicating refractory die and crown were measured, and the crown distortion was tested with low-viscosity elastomer (fit-checker and bite-checker). Thermal expansion were measured in both duplicating refractory die and porcelain. The boundary area between porcelain and duplicating refractory die was also analyzed with electron probe micro analyser (EPMA).
All duplicating refractory dies showed expansion compared to the master die.
The all-ceramic crowns fabricated on the duplicating refractory die in all processes, had a good fit with satisfactory expansion. However, high-fusing ceramics made by the core-finishing process (VITA Hi-ceram), had an inferior fit.
It was considered that shrinkage of the-duplicating refractory die during the porcelain sintering process and adhesion between the porcelain and duplicating refractory die were dominant factor in the shrinkage of the crown. The distortion of the crowns was mainly considered to be influenced by the distortion of the duplicating refractory dies.

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The hardness and the elastic modulus in the compression of six commercial denture base soft lining materials were investigated. The testing apparatus was a modification of the hardness test meter designed by Inoue et al. (1985) for oral soft tissue. The values obtained by this instrument were compared with the results from two other methods (a Dulometer and an Autograph). The hardness values of all the materials increased slightly with the time elapsed after setting. This result correlated well with the hardness values obtained by the Dulometer. The elastic modulus in compression at 37℃ of the test specimens stored in an air cabinet at 37±0.5℃ for 24 hr after setting was 87.2×10⁶ dyne/cm² for olefin polymer, 25.9×10⁶ dyne/cm² for fluoro polymer, 3.58×10⁶ & 26.4×10⁶ dyne/cm² for silicone materials and 4.96×10⁶ & 6.46×10⁶ dyne/cm² for acrylate materials. The modified instrument was considered satisfactory for examining the mechanical properties of soft lining materials, impression materials or oral soft tissue.

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A glass surface treated with silane coupling agents such as 3-methacryloxypropyl-trichlorosilane (3-MPST) and-trialkoxysilane (3-MPS), and the fractured surface of the glass plate after a bond test were analyzed by scanning electron microscopy, scanning tunneling microscopy, Raman scattering spectroscopy and infrared reflection-absorption spectroscopy. The trichloro silane (3-MPST) with active hydrolyzable groups reacted more strongly with water and silanol on the plate. Multilayers consisting of siloxanol oligomer and/or polymers were produced by hydrolysis of the silanes followed by condensation of the products and uniformly covered the surface of the plate. The bond strength of the resin to the plate treated with 3-MPST after 2, 000 thermal cycles was better than that of 3-MPS. The failure of the bond between resin and the plate treated with 3-MPST showed cohesion fracture, while that of 3-MPS was glass plate-resin interface separation.

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This study examined the effects of surface treatment on the shear adhesive strenght of cements to castable glass ceramics. Castable glass ceramics (calcium metaphosphate) and four different dental cements (glass ionomer, polycarboxylate and two types of adhesive resin) were used. Cylindrical castable glass ceramic rods were cast for the shear adhesive strength test. Each was given a different surface treatment. The five different surface treatments were: group 1. polishing with 600 grit SiC abrasive paper; group 2. polishing with 120 grit SiC abrasive paper; group 3. sand blasting with alumina; group 4. HF containing etching solution; and group 5. wetting agent for porcelain. The rods in each group were cemented to each other. Using a film thickness adjustment apparatus, the film thickness of dental cement was adjusted to 50 μm and specimens were stored at 37℃, 100% relative humidity. The shear adhesive strength of each dental cement was measured 1 day after, 1 week after, 1 month after and 3 months after the rods were cemented. Shear adhesive strength of glass ionomer cement and polycarboxylate cement to castable glass ceramics polishing with 600 grit SiC abrasive paper were not obtained, 120 grit SiC abrasive paper were very low and HF containing etching solution was the most effective surface treatment. As for the influence of storage period in 37℃, 100% relative humidity on shear adhesive strength, all dental cements decreased in strength overtime, but statistical difference was observed only after 3 months.

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The CAM process of a CAD/CAM system for laminate veneer restoration was developed. Laminate veneer shells were milled of ABS resin. To correlate the position of upper and lower side of shell, a precision vise and a rectanglar ABS resin block of 20.0×30.0×25.0 mm were used.
Ball-end mills 2.0, 1.0 and 0.5 mm in diameter were used for rough, medium and final manufacturing, respectively. Tool offset for the radius of each ball-end mill was given in the Z direction.
Consequently, a CAM system to mill the labial and inside surfaces of laminate veneers was developed and laminate veneers can be manufactured with high accuracy.

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To establish a cell recovery testing method, the effects of the initial cell number, treatment time and recovery time were examined with respect to temperature and pH value of the medium and the addition of metal ions to the medium. Cells used were L-929 fibroblasts and HEp-2 human larynx epithelial cells. A temperature of 40℃ had a slight effect on cell recovery. However, at longer treatment times, cell recovery was markedly reduced at 4℃, 43℃ and 46℃, respectively. Almost no cell recovery was observed at 49℃. Similar results were obtained under experimental conditions with two different recovery times of 4 days or 7 days and four initial cell numbers of 3×10² cells/ml, 1×10³ cells/ml, 5×10³ cells/ml or 2×10⁴ cells/ml in both cell lines. A pH of 6 had no effect on cell recovery. At a pH of 5, cell recovery was reduced in both cell lines and for both recovery times at longer treatment times and lower initial cell numbers. Cell recovery was negligible at a pH of 3 and 4 in both cell lines. Ag ions over 0.01 ppm decreased cell recovery in both cell lines with longer treatment times and lower cell numbers. Ag ions markedly decreased cell recovery at 5 ppm and 10 ppm. Pd ions over 0.5 ppm and Cu ions over 0.5 ppm or 1.0 ppm had similar effects.
The present results revealed a relationship between change of temperature and pH values of medium and addition of metal ions, and initial cell numbers, treatment time and recovery time. The effect of cell damage due to physical and chemical stimuli on cell recovery was discussed.

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Microwave vulcanization was applied to the bond between the metal plate and LTV vinyl silicone rubber (VS) to examine ways of decreasing the working time. As a metal plate, two kinds of Co-Cr alloys and a Ni-Cr alloy were used. For the control, pure copper was used. Two kinds of dual typed VS of RTV and LTV, and an LTV VS were used. Metal plates were sand-blasted and abraded after casting. The bonding area of the metal plate to VS was 10×10 mm. One or three mm thick pieces of VS were prepared and vulcanized after investment in an FRP flask. Vulcanization by microwave was done at an output of 500 W of heating and irradiation time was 5 or 7 min. For the control, specimens were vulcanized in water at 100℃ for 90 min.
As a result, in the specimens vulcanization by microwave, bond strength showed a tendency to increase irradiation time increased. Furthermore, in the 1 mm thick VS specimens, bond strength was high compared with that of 3 mm thick specimens. It was also demonstrated that the value of a bond strength depends upon the kind of VS rather than the metal plate. The bond strength of the microwave vulcanization (14-29 kgf/cm²) was comparable or superior to that of water bath vulcanization, and was faster than vulcanization with conventional hot water.

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The grain boundary reactions in Ag-25 mass% Pd-10 mass% Cu alloys with addition of 0.01 mass% aluminum were investigated by optical microscopy, electrical resistivity measurement, hardness test, and SEM observations. The grain boundary reactions in the alloys were retarded by adding 0.01 mass% aluminum. Nodules for the Al adding alloys aged at 400℃ did not appear up to 10³ min. The retardation effect of adding 0.01% Al on the grain boundary reaction was larger than that of adding 1 mass% Sn.

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The interaction of eugenol (EUG) and its related compound (guaiacol, phenol and safrole) with dipalmitoylphosphatidylcholine (DPPC) was investigated by differential scanning calorimetry (DSC) and by NMR spectroscopy, to elucidate their activity at the membrane level. EUG with phenolic OH and allyl group markedly lowered the endothermic phase transition temperature (Tm) compared to that of guaiacol, phenol and safrole.
¹H-NMR spectra of DPPC/EUG (2:1 molar ratio) and DPPC/cholesterol/EUG (2:1:1) showed EUG signals markedly broadened in a wide temperature range (18〜52℃). EUG signals at 18℃ shifted significantly to a higher field (shielding). It was concluded that EUG has a strong interaction with DPPC liposomes.

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Cytotoxic effects induced by ten commercial dental alloys manufactured in Japan and the People's Republic of China in vitro by evaluating cell recovery after extraction with artificial saliva were examined in mouse fibroblast cell lines of L-929 cells and human larynx epithelium cell lines of HEp-2 cells. Co-Cr alloys, Ag-Pd-Au alloys, Ag-Zn-In-Sn alloys, Ag-In-Zn alloys, and Ti-6Al-4V alloys showed little effect. The Ni-Cr alloys had a slight inhibitory effect and the Cu-Al-Ni alloys had a marked effect. Dissolution of metal ions in the extracts was measured in the alloys affecting cell recovery. The present findings were discussed considering the use of artificial saliva in cytotoxicity testing.

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This study examined etching techniques by comparing tensile bond strengths with the concentration of phosphoric acid in etching agents to establish a technique that minimized adverse effects on human enamel. Enamel surfaces of human premolars were polished with an abrasive containing hydroxyapatite and then etched with the etchant for 30 s. Five wt% of aqueous phosphoric acid achieved sufficient for the enamel etching to afford the same bonding strength as 65 wt% acid. These data suggest that it is not necessary to use more concentrated phosphoric acid which could more severely demineralize the enamel surface.

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The hardening characteristics of zine oxide eugenol (Ha, Me), polysulfide rubber (Su) and silicone rubber (Co, Xa, Ex, Pr, Si) as impression materials for ridges with flabby tissue, were measured at 23℃ and 37℃, or only 23℃ by loads using glass plates (0.5, 1.0, 1.5 kgf), a reciprocating rheometer and stress relaxation apparatus.
The measurements in three types of materials were different from each other, but those in the same type were considerably similar to each other and indicated that Ha and Pr respectively were softer than the others.
So the measurements of Ha, Su and Pr were evaluated.
1. Hardness just after completion of mixing: Pr was softest.
2. Duration of softness: Ha>Su>Pr
3. Working time and setting time: Pr was shortest.
4. Rapidity of the hardening reaction: Ha>Pr>Su
5. Dependence on load just after completion of mixing: Ha>Pr>Su
6. Dependence on temperature: Ha>Su>Pr
The impression materials for flabby ridges should be selected with consideration of these hardening characteristics. The order of preference might be strongly influenced by the experience of the dental practitioner (e.g.: time required for impression procedure, settling force of impression tray).

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Modification of tooth surfaces with metallic ion for tooth-bonding was investigated by treatments with chelating agent and metallic ion. Phytic acid (PYA) was used as a chelating agent and tin (II) fluoride (SnF₂) was used as a source of metallic ion. The effects of these treatments were evaluated by the shear bond strength of Photo Bond^® to bovine dentin and enamel.
The bond strength to dentin treated with 3〜10% solutions of PYA and then with saturated solution of SnF₂ was in the range of 9〜10 MPa.These values were the same as that of dentin treated with K-etchant^®(40%-phosphoric acid) and higher than 6〜7 MPa of dentin treated with PYA solutions only. The bond strength to enamel treated with 5 and 7% solutions of PYA and then with SnF₂ solution was 16 and 18 MPa, respectively. These values were higher than that 14 MPa of enamel treated with K-etchant and 11 MPa of enamel treated with PYA solutions only. The bond strength to dentin and enamel treated with PYA and SnF₂ solutions was maintained after 3, 000 thermo-cycles (4-60℃). Innumerable spherical deposits, which were suspected to be chelate compound of PYA and Sn²⁺, were observed on the dentin surface treated with PYA and SnF₂ solutions. From these results, it was suggested that the interaction between the functional monomer, MDP, contained in Photo Bond and Sn²⁺ contributed to the bonding.

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