The dimethacrylates of different molecular lengths, such as ADMA, EpDMA and BdDMA, were synthesized and the properties of their cured resins were studied to determine the relation between the structure and the physical and mechanical properties. The cured EqDMA that contained aromatic rings had less polymerization shrinkage and thermal expansion than the cured aliphatic ADMA, EDAM and BdDMA resins. Water absorption of the cured ADMA and BdDMA decreased, as the hydrophobic chain length increased. As a result of the favorable combination of the rigidity of aromatic ring and the long chain flexibility, the transverse strength of cured EpDMA increased with the increase in the distance between cross-linked points in the EqDMA polymer network. The terpolymer EpDMA/BdDMA/MMA (of ADMA, EDMA), had the maximum transverse strength and deflection when fine phase-separated particles (0.5 μm) consisting of soft BdDMA segments appeared on the SEM micrograph.

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To improve the adhesion between the silicone resilient liner and acrylic denture bate, two experimental adhesives were prepared, one was a γ-MPTS/EA copolymer dissolved in toluene for the condensation RTV silicone rubber, and the other was the condensation product between HEMA/MMA copolymer and DMVCS dissolved in toluene for the addition RTV silicone rubber. Acrylic rods and condensation or addition RTV silicone rubber were bonded with these adhesives.Their bonding durabiity was evaluated by the measurement of tensile bond strength after the bonded specimens were kept in 80℃ water for a certain time. The acrylic rods bonded to the addition RTV silicone rubber with the experimental adhesive showed excellent durability against hot water; that is, the tensile bond strength of the bonded specimens did not change, after the specimens were kept in 80℃ water for ten days. Therefore, the silicone denture liner with high bonding durability can be developed by the application of this experimental adhesive.

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Mechanical properties (transverse strenght, elastic modulus and compressive strength) and water sorption characteristics of five types of urethane dimethacrylate (UDMA)-1, 6-hexamethylenglycol dimethacrylate (HMDMA) systems were evaluated under dry and wet conditions to improve the resistance of watre sorption of UDMA resin systems. The mechanical properties of each UDMA-HMDMA system showed optimum strength when the UDMA concentration was 50 to 70 mol%. The UDMA monomers containing additional phenoxy groups gave copolymers with slightly lower mechanical properties than the monomers. In the UDMA-HMDMA system, the mean water sorption was low, and the mechanical properties slightly reduced by immersion in water were comparable to those of UDMA-triethyleneglycol dimethacrylate (triEDMA) systems. These findings suggested that the employment of HMDMA as a diluent monomer would improve the resistance of water sorption of UDMA resin system.

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Some physical properties of the luting cements, zinc phosphate cement, polycarboxylate cement, glass ionomer cement currently on market were examined in relation to various powder/liquid ratio, and for their fulfilment of Japanese Industrial Standards (JIS) T-6602 for dental zinc phosphate cement and American Dental Association Specification No. 8 for zinc phosphate cement. 1) Some physical properties of zinc phosphate cement were similar to traditional reports. 2) Although film thickness of polycarboxylate cement was smaller, other physical properties were similar to traditional reports. 3) Altghough film thickness and solubility of Fuji ionomer Type I and Keatc-cem were smaller than previously reported, other physical properties and physical properties of HY-BOND Glasionomer-c were similar to traditional reports.

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To study the effect of isocyanatosilane coupling agents such as 3-methacryloxypropyl triisocyanatosilane (3-MPSN) on the silica surface, the reactivity of the isocyanato groups with water and adhesive tensile strength of poly (methyl methacrylate) to glass plate and porcelain treated with the silane after immersion in water at 37℃, were measured. The isocyanato groups reacted more strongly with watre than the alkoxy group of 3-methacryloxypropyl trimethoxysilane (3-MPS) confirmed by the adhesive strength of the resin to glass plate and porcelain, and by FTIR-ATR spectroscopy. On the glass plate, multilayers consisting of siloxanol oligomers and/or polymers were produced by hydrolysis of 3-MPSN followed by condensation of the products. Based on the results obtained, it is suggested that better water-resistant adhesion of isocyanatosilanes having active hydrolyzable groups to mineral surfaces groups depends on formation of the siloxane bond between the agents and the mineral substrates and a higher degree of crosslinking in the siloxane phase.

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Seven experimental investments distributing the three grain sizes of crushed electrically fused calcia powder, i.e., coarser powder (100-200 mash), medium-sized powder (200-325 mash) and finer powder (325 meth pass) were prepared and the manipulatory characteristics, the strength of set investments and the surface texture of titanium castings were investigated. Calcia investments containing 75-90 wt% of the finer powder, 5-15 wt% of the mediumsized powder and 5-10 wt% of the coarser powder had better manipulatory characteristics with methanol and set completely within 24 hours at 23℃. The green strength of these investments was 9.1-10.5 Mpa and the fired strength, 10.0-10.9 MPa. Titanium castings with all experimental investments showed a glossy surface that did not react with the mold in spite of the high mold temperature of 1000℃. Especially the castings with calcia investments containing 75-90 wt% of the finer powder had an excellent surface, which had a roughness of 1.07-1.14 μm(Ra).

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The dimensional changes of 20 products of alginate impression materials in viral disinfectant solutions (0.1〜1% sodium hypochrolite, 2% potentiated glutaraldehyde, 25〜70% ethyl alcohol and 0.07% Povidone-Iodine) were measured, and the optimal disinfection treatment was determined with respect to the dimensional stability of alginate impression materials common to the products. The immersion of alginate impressions in 0.07% Povidone-Iodine solution for 10 minutes is optimal as a general disinfection treatment, and the immersion in 0.5% sodium hypochrolite solution for 15 minutes is suitable in the case of heavy contamination.

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To clarify the influence of dental metallic salts on biologic membranes, we investigated the phase transition properties (transition temperature, T; enthalpy, ΔH; entropy, ΔS; ΔT_1/2; H/HHW value) of L-α-dipalmitoylphosphatidylcholine-cholesterol (DPPC-CS) liposomes induced by AgNO₃, Ag(NH₃) F, NaF, NaOCl, KI, CaCl₂, FeCl₃, ZnCl₂, ZnI₂, etc.using differential scanning calorimetry (DSC). Monovalent ions(Ag⁺, Na⁺, K⁺, F^-, NO₃^-) had a small effect on the DSC properties of DPPC-CS liposomes, while divalent ions (Zn²⁺) due to ZnCl₂ and ZnI₂ had a large effect. The chloride salt of Ca²⁺ had a small effect on the lipid DSC properties. The chloride salt of Fe³⁺ had the largest effect on the DSC properties. We also studied the DSC properties of unsaturated phospholipid liposomes (L-α-phosphatidylcholine β-stearoyl-γ-oleoyl; PCSO) induced by I₂, I^- and OCl^-. Such polarizable anions and iodide strongly affected the DSC properties, probably due to the halogenation of double bone in the acyl chains of PCSO.

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Fracture toughness(K_IC), a useful indicator of marginal fracture resistance and wear resistance which are important properties for dental composite resins, was measured. Six visible light cured composites with different filler contents (0-64 vol%) were prepared experimentally. Fracture toughness, compressive prool strength, diametral tensile strenght, bending strength and bending elastic modulus of these composites were measured. Single edge notched three-point bending specimens were employed for fracture toughness measurement. Fractography was performed on the tested specimens by scanning electron microscopy. A positive correlation against volume filler content was obtained for every mechanical property. Fracture toughness (K_IC) of the unfilled resin and the composite resin with 64 vol% filler were 0.604 MPa √m and 1.409 MPa √m, respectively. The reinforcement effect of filler compound was greater in low filler content composites (0-30 vol%) than that in high filler content composites (30-64 vol%). Interestingly, other mechanical properties did not show this tendency. Increase of surface energy, absorption of fracture energy by small crack formations and crack-pinning effect by filler particles are considered to contribute to the fracture toughness of particle reinforced composites.

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A measuring method of polarization resistane (Rp), Coulostatic method has been recently applied to rapidly determine the corrosion rate of alloys in the metallurgical area. Corrosion rate(I_corr) is obtained using the following equation; I_corr=K/Rp (K: constant value). The value of the method in evaluating I_corr of dental alloys which have a high corrosion resistance was determined. Six kinds of Ag-Pd alloys, four kinds of Ag-Pd-Cu alloys, one Ag-Cu alloy, and four kinds of commercial dental Ag-based casting alloys were used for the specimen and a 0.1% HCl Ringer solution at pH=2, was used as the test solution in the study. Polarization resistance of the specimens was measured every 24 hours by the Coulostatic method for 20, 40, 60 days. I_corr of the alloys was calculated from mass loss and amounts of elements eluted into the solution by Faraday's law. K values were obtained using the equation. In summary, I_corr which changed in proportion to 1/Rp, ranged from 2.3×10^-8 at minimum and 4.4×10^-5 (A/cm²) at maximum, whereas the K values were localized between 13.5 and 25.9 mV. The average K value was 20 mV. Therefore, the I_corr of dental Ag-based alloys was estimated simply from the Rp substituting 20 mV for K of the above equation. These findings revealed that the Coulostatic method is useful for rapid determination of the corrosion rate of dental alloys.

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Studies have been undertaken to apply the CAD/CAM system to Dentistry and to make prosthetic appliances automatically. 3D measurements were made with a digitizer developed from the portable 3D modeling machine with sensing functions. The specimen was a 4 times larger plaster model. The outstanding merit of this method is that the measuring points can be selected by the operator or the dentist. Interpolation of these 3D data using spline function gave just as good results as those obtained using linear interpolation. Spline interpolation was very useful in cases having few points as in the present sample. This method was concluded to be in our Dental CAD/CAM system.

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Titanium sapmles were immersed in hydrochoric acid, sulphuric acid, hydrofluoric acid, and chemical polishing bath (mixture of hydrofluoric acid and nitric acid) and the meltage, the surface roughness, and the surfece texture were examined. Warmed hydrochloric acid and sulphuric acid showed the solubility of titanium but their meltage were much smaller than the hydrofluoric acid and were found useless in practice. Hydrofluoric acid caused high meltage with a low concentration at room temperature, and was found useful to remove even the hardened layer of titanium castings in a short time. The chemical polishing bath did not cause much meltage but improved the surface roughness and surface texture, and was considered useful for the middle finishing of titanium prosthetics.

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The model investment method using zirconia investments was developed to cast a full denture bese with pure titanium. The new zirconia investments were composed of the refractory oxides: calcia stabilized zirconia(<200+<325 mash)+10 mol% calcia and the binders: zirconyl acetate+zirconia sol. The liquid/powder ratio is about 0.21. Silicone impression materials were used for impression taking. The casting of titanium was done using an argon arc melting castor with the preheat temperature of the model 950℃. Only one sprue without any chill or vent for wax up was enough for the cast into the whole pattern. The defects inside the castings were examined by the transmission X-ray method. The denture castings were of the surface with the metallic gloss as cast and of adequate dimensional adaptability.

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Using bonding agents and resin adhesive for two commercial composite core materials which had a different setting contraction, we investigated the bond strength to human dentin by the pull out method from root canal cavity. The bond strength of core materials with a small setting contraction (0.33%) is larger than that of the material with a large contraction (0.91%). The bond strength decreased with the decrease in core length and increase in the taper of the cavity wall, but the effects of core length or taper were not as strong as the effect of a matal core. These effects were small due to the large bond strength of the adhesive. When cementing the prefabricated core in the root canal cavity after extracting the core from the cavity, the influence of setting contraction on the bond strength is negligible. The use of resin adhesives such as Superbond containing 4-META and Panavia EX containing a phosphate ester, was very effective and the bond strength became twice the value of that obtained by the ordinary direct filling method. However, the bonding agents were not useful for attachment to the core material.

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To accelerate the degradation in water of composite resins, samples were stored in boiling water in a pressure cooker for a week and subjected to the tensile test, measurement of the surface roughness and SEM observation. Samples stored in distilled water at 37℃ for one week had decreased tensile strength and lowered equilibrium in Young's modulus, and the physical degradation by water sorption was considered to be caused by this condition. Samples stored in boiling water for one week showed both a decreased tensile strength and in Young's modulus, and the increase of surface roughness. SEM photographs of the fractured surface showed the traces of separation of the filler from matrix resin. The chemical degradation was considered to have been caused in samples stored in boiling water to accelerate the degradation of composite resins in water and the durability of composite resins could be evaluated in a short time by the direct tensile test of samples stored in this condition.

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Polymerization of the MMA/TBBO resin was investigated in the presence of a collagen sheet treated with various treatment solutions in order to clarify the mechanism of effectiveness of ferric ion in the abhesion between MMA-PMMA/TBBO resin and dentin. The treatment solutions employed were aqueous solutions of ferric chloride (FC) or various ferric salts and citric acid (CA). Although FC-CA solution hindered polymerization of MMA at high FC concentrations, curing time of the resin decreased by the dilution of the treatment solution. Polymerization was promoted most effectively by the treatment solution of 0.50 wt% FC-1.67 wt% CA.The polymers formed were separated mechanically and by stepwise extraction. The molecular weight of the polymers depended on their location. The value was higher for polymers located closer to the inside of a collagen sheet. When the treatment solution promotes polymerization of MMA, FC-CA solution, in the presence of collagen, may improve adhesion of MMA resin to dentin through first fast curing of the resin inside collagen, the enhanced molecular weight of polymer inside collagen and graft polymerization onto collagen.

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Titanium was mechanically polished using two kinds of electrodeposited diamond wheels (R, F) under a 100 g load and rotational speed of 250-1000 m/min for 90 seconds. Polishing by the diamond wheel R caused a higher amout of polishing and improved the grinding ratio as the rotational speed increased. The amount of polishing and the grinding ratio by the diamond wheel F also increased as the ratational speed increased but the value was much smaller than that diamond wheel R. The surface texture by the diamond wheel F was found superior to that by the diamond wheel R. Diamond wheels were found more useful for polishing titanium than carborundum wheels. The diamond wheel R should be useful in obtaining a coarse finish and diamond wheel F for medium finish in practical use.

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The fundamental conditions necessary for producing a new type of light, silent and fashionable air turbine handpiece at a low cost were examined. The relationship between air pressure and rotational speed was examined. The results were recorded on log-log graph paper with the rotational speed on the vertical axis and the air pressure horizontally. The plot gave a straight line. Secondly, the 1/3 octave sound frequency analysis showed a sharp peak at center frequency band including frequency which was the same as the speed of rotation, i.e., rotational frequency. In conclusion, the noise from air turbine bandpieces for dental use is generated by the mechanism in close relation to the rotational speed and noise source can be regarded as simple sound source (monopole) judging from directional characteristics of noise and distance attenuation.

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The effect of several resin monomers on the glucosyltransferase activity of Streptococcus mutans was examined. The glucosyltransferase activity was estimated from the radio activity of ¹⁴C-glucose incorporated into water insoluble glucan. The eluate from cured resins immersed in KPB (potassium phosphate buffer) stimulated the synthesis of water insoluble glucans.In the individual resin monomers, di-, tri-, and tetra-ethylene glycol dimethacrylate (2G, 3G and 4G), Bis-GMA and UDMA enhanced the production of water insoluble glucans, but ethylene glycol dimethacrylate (1G), polyethylen glycol dimethacrylate (9G, 14G), and MMA diminished the synthesis of water insoluble glucans. Especially, 3G enhanced the production of both insoluble and soluble glucans. In addition, the eluate from experimental resin consisted of 1G and Bis-GMA, diminished the production of water insoluble glucan compared to those from 3G and Bis-GMA based resins. These results indicated that it was possible to develop a composite resin which inhibits the accumulation of plaque by using the antienzymatic monomers.

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The photopolymerization of a photocurable bonding liner was analyzed by DSC. The influence of amines and 4-MET on photopolymerization of the liner was qualitatively evaluated. 1. N-phenylglycine (NPG) acts as a reducing agent and it is more effective in an acidic condition. 2. Combination of N, N-dimethylaminobenzene derivatives with 4-MET promotes the rate of photopolymerization of the liner. 3. Combination of aliphatic tertiary amine with 4-MET delays the rate of photopolymerization of the liner. 4. Effect of aromatic and aliphatic amine hydrochlorides as a reducing agent is not observed on the photopolymerization. 5. Pretreatment with an EDTA solution which contains Fe³⁺ improves the tensile bond strength to bovine dentin, but addition of excess Fe³⁺ to the liner inhibits the photopolymerization.

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