We examined the relationship between collagen crosslinking techniques and dentinum reinforcement. In the present study, the tensile tests, imbibition test and antienzyme test were performed on collagen films mainly composed of type I collagen after ultraviolet irradiation and immersion in tannic acid and glutaraldehyde. The elastic modulus increased with the reaction time, but reduction of elongation at breaking point and increased stiffness were observed. This tendency was enhanced by ultraviolet irradiation. Tannic acid treatment resulted in slower crosslinking than the other two techniques. Antienzyme activity was markedly increased by treatment with tannic acid and glutaraldehyde.

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An original CAD process for bridge restoration was developed, and CAD for a maxillary left three unit bridge was attempted. The measured shape data of the standard crown of a second premolar and molar were deformed, and were applied on the dies. The measured pontic data were inserted between two molars. Here, bite data of the opposing teeth were introduced, and the occlusal relationship with the applied molars was adjusted. The bite data were then replaced by the FGP data, and the occlusal surface interference with FGP data was eliminated. Connection processes were then carried out. The clearances between the pontic and molars were filled with interpolation, and the ends of the applied second molar and premolar were connected with the margin of each die. Finally, the data above the margin of each die were extracted, and used as the inner crown data for the bridge. The whole bridge was designed using a newly developed computer program.

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To improve the water sorption of poly (methyl methacrylate), new hydrophobic monomers, such as norbonyl and phenyl methacrylate, were studied to determine the resin with lower water sorption with no decrease in mechanical property. Water sorption of the copolymers of the hydrophobic monomers and MMA decreased with the increase in the concentration of the monomers. Compressive and bending strength of the copolymers were higher than that of PMMA, and the elastic modulus in bending was the same as that of PMMA. In addition, the transverse-deflection values satisfied ADA specifications. Dynamic mechanical thermal analysis of the copolymers showed a similar tendency to that of PMMA in spite of the introduction of bulky groups, such as norbonyl and phenyl, in the polymer molecule. The polymerization shrinkage in volume was in the following order: norbonyl<phenyl<methyl methacrylate.

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As a part of a series of studies to examine the role of the initiator system in dentin bonding, the effectiveness of a new polymerization initiator system consisting of 2-methyl-1, 3-cyclohexanedione (MCHD) and CuCl₂ in dentin bonding was investigated in terms of the effects of dentin conditioners and CuCl₂ concentration formulated in MMA/PMMA resins. Curing time and tensile bond strength to bovine dentin were measured using resins composed of MMA containing 0.001-0.03wt% CuCl₂ and PMMA powder containing 2wt% MCHD. The dentin surfaces were treated with six conditioners consisting of 10wt% phosphoric acid or citric acid containing 0-3wt% FeCl₃ or CuCl₂. The bond strengths of about 10MPa obtained under optimal conditions were comparable to those reported for tributylborane-initiated MMA resin which is one of the most effective bonding resins available. Thus, the resin using MCHD/CuCl₂ system was concluded to be very effective for dentin bonding, especially when dentin was treated with acidic conditioners containing ferric or copper chloride.

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An experimental primer was developed as a single-step bonding system for resin-modified glass ionomer cements (GIC). Efficacy of this primer on adhesion of resin-modified GICs and resin composite to enamel and dentin was evaluated by shear bond test and SEM observation. Good bond strengths to enamel were obtained (>11MPa), whereas significantly low bond strengths to dentin were obtained using a single coat of the primer. However, double-coating improved the bond strengths to dentin (>8MPa). SEM observations indicated that the primer functioned as a mild conditioner to remove the smear layer on enamel or dentin surfaces. A hybrid layer was observed at the cross-sectional view of the GIC/dentin interface. These findings suggested that good adhesion to enamel and dentin could be achieved using a single-step bonding system.

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Expansion of a gypsum-bonded investment mold was investigated using a fused quartz tube pattern. Two hours after mixing, a fusible alloy was cast into the space around the pattern induced by setting expansion. The other molds were heated up to 700°C, then a dental silver alloy was cast into the space around the pattern induced by total expansion of the mold. Thickness of the castings was measured at every thirty degrees on seven cross-sections. The setting expansion was almost uniform, but the total expansion was not. Especially, a large amount of total expansion was produced toward the open ends of the casting ring and toward a seam of the asbestos liner. The thermal expansion of the mold was anisotropic because the investment was a mixture of calcium sulfate and silica, and was affected considerably by its environment.

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Experimental light-cured composite resins were exposed to a narrow-band light at a constant quantum number using a narrow-band interference filter. The IR spectra of the cured resin specimens were measured before and after extraction of residual monomers. Degree of conversion (DC) and polymerization conversion (PC) were calculated from these IR spectra. The light in 410-550nm could be polymerized. With a brief exposure (5s), DC and PC were affected by the wavelength. The effect of wavelength between 410 and 490nm decreased with increasing duration of exposure. The most efficient wavelength was 470nm and the most adequate wavelength was in the 450-490nm wavelength range. The absorbance of camphorquinone strongly affected polymerization, especially during the initial stage. However, from the relationship between DC or PC and exposure energy, polymerization depended not only on the wavelength of the light, but also on the exposure energy.

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The present study was conducted to examine the effect of the addition of a dimethacrylate to resin cements on bond strength between titanium and resin after thermocycling. Titanium disks, polished and treated with a phosphate monomer, were bonded to acrylic rods using two types of experimental resin cements. The cements were composed of methyl methacrylate (MMA) containing a tributylborane initiator and 0-10wt% of ethylene glycol dimethacrylate (EGDMA) and two types of polymer component of hard poly (MMA) or soft fluoropolymer (2-6F). The bonded specimens were subjected to a thermocycling test in water and then to tensile strength testing. The addition of 5% or more dimethacrylate monomer to the two MMA-based resin cements caused a drastic decrease in bond strength to the metal after the thermocycling test. The resin prepared with soft 2-6F as a polymer component was significantly more durable than the rigid type resin based on PMMA. However, even a 1% addition of EGDMA to the 2-6F resin resulted in a significant decrease in durability.

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Thermal diffusivity and specific heat of four groups of dental casting alloys (Ag-based, Au-Pd, high karat and Ni-based alloys) were determined. Measurements were carried out from room temperature to 750°C in an evacuated electric furnace with a laser flash thermal constant analyzer. There was no significant difference between the values of thermal diffusivity in the Ag-based and high karat alloys; 18-24 and 40-53mm²/s, at room temperature and at 600°C, respectively. For Au-Pd and Ni-based alloys, diffusivity was 8-12 and 3-4mm²/s at room temperature, and 19-22 and 5-6mm²/s at 600°C, respectively. The thermal diffusivity of the alloys was significantly low compared to that of the pure-metals of which they were composed. Specific heat was determined as 0.14-0.16, 0.24-0.34, 0.17-0.19 and 0.45-0.51kJ/(kg⋅K) for high karat, Ag-based, Au-Pd and Ni-based alloys, respectively, at room temperature. Oxidation of the Ni-based alloy at elevated temperature affected the value of specific heat measured.

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The present study examined the effect of crosslinking of resin cement on durability of adhesion between titanium and resin against repeated thermal stress. Titanium disks, polished and treated with a phosphate monomer, were bonded to acrylic rods with resins composed of poly (methyl methacrylate), methyl methacrylate containing 0∼5% dimethacrylates or diacrylate as crosslinking agent, and a benzoyl peroxide/amine initiator system. The bonded specimens were subjected to thermocycling in water and then tensile strength testing. The addition of 5% crosslinking agent, irrespective of its type, to the resin resulted in a significant decrease in bond strength after 500 thermocycles. No significant difference in durability was revealed among the five crosslinking agents studied.

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