Long periods can be required to determine the color stability of acrylic resins. The concentration of propagating radicals with unpigmented experimental resins (UER) and initiator solution (IS) of two initiator systems (binary and ternary) and five products were measured using electron spin resonance (ESR). The radical concentration was estimated from the area under the integrated ESR spectrum. The discoloration was measured using a color computer. Higher content of benzoylperoxide led to higher radical concentrations. The radical concentration for the ternary system increased slightly with time, but were lower than those of the binary system. Significant positive correlations were found between the radical concentration and ΔE^*ab for UER (r=0.900, p<0.01), IS (r=0.953, p<0.001) and the products (r=0.808, p<0.05). It was suggested that the color stability of these resins was predictable by measuring the radical concentration using ESR.

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Phase transformation behaviors in Au-Cu-Pd alloys were investigated by means of electrical resistivity measurements, hardness tests, X-ray diffraction and transmission electron microscopy. Anisothermal and isothermal annealing were performed. Two types of phase transformations were found, namely related to the single phase of Au₃Cu and the coexistent phase of Au₃Cu and AuCu I. The latter produced more remarkable hardening than the former. Hardening was brought about by the antiphase domain size effect of Au₃Cu ordered phase in the single phase and by the formation of AuCu I ordered phase in the Au₃Cu ordered matrix. There are three modes of phase transformation in the coexistent region depending on the composition. Each sequence is discussed.

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Phase transformation mechanisms in the AuCu-Pd pseudobinary system were studied by means of electrical resistivity measurements, hardness tests, X-ray diffraction and transmission electron microscopy. A direct aging method was employed to eliminate the otherwise unavoidable ordering that takes place rapidly during quenching into ice brine, hence it is important to distinguish the ordering processes with and without an incubation period. Three phase transformation modes occurred, namely; ordering at grain boundaries and in the grain interior with nucleation and growth mechanism after incubation, and spinodal ordering without any incubation period. The age-hardening of the alloys examined was attributed to AuCu I ordering. Nucleation and growth mechanism followed by twinning occurred in the specimens aged at higher temperatures, while spinodal ordering was seen in specimens aged in lower temperature. The spinodal ordering temperature of AuCu-Pd alloys increased according to Pd content.

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Qualitative and quantitative analyses were conducted on four kinds of resin-modified glass ionomer (RMGI) cement liquids, LC, LC II, LC III (hereinafter referred to as LCs) and VM, using HPLC and laser Raman spectroscopic methods. HPLC revealed that among the RMGI liquids LCs contain 31-32% HEMA (2-Hydroxyethyl methacrylate), and VM contains 18% of the same. The composition of RMGI cement liquids varied significantly between manufacturers. In Raman spectroscopic analyses, the spectra of liquids of various ratios of polyacrylic acid and HEMA were measured, and calculations were made on the peak intensity ratios of C=C stretch vibration to C=O stretch vibration, common in both HEMA and polyacrylic acid. The composition ratio of polycarboxylic acid to HEMA of commercial glass ionomer cements was assessed by the regression curve generated by a combination of peak intensity ratios and composition ratios. In addition, Raman spectroscopy was able to identity the differences in form of the methacryloyloxy group.

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Calcium phosphates were formed on five kinds of substrate metals using a hydrothermal-electrochemical method in an autoclave with two electrodes. The electrolyte dissolving NaCl, K₂HPO₄, CaCl₂⋅2H₂O, tris (hydroxymethyl) aminomethane, and hydrochloric acid was maintained at 100°C, 150°C and 200°C. The counter electrode, the anode, was platinum plate, 20×20×0.5mm, and the working electrodes as cathode were pure titanium, pure zinc, pure nickel, pure iron, and stainless steel plates. A constant direct current at 12.5mA/cm² was loaded for 1hr. Hydroxyapatite [Ca₁₀(PO₄)₆(OH)₂] only deposited at three temperatures on pure titanium plate. On pure zinc plate, both parascholzite [CaZn₂(PO₄)₂⋅2H₂O] and hydroxyapatite were formed at 150°C and both parascholzite and ZnO were formed at 200°C. Both hydroxyapatite and β-TCP [β-Ca₃(PO₄)₂] were formed on pure nickel, pure iron, and stainless steel plates at 200°C. It seems that the incorporation of the metal ions released from the electrode decreased the Ca/P ratio of the deposit due to the formation of other compounds except hydroxyapatite.

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The aim of this study was to assess the toxicological responses of a resin composite containing TiK₂F₆ and NaF in rat dental pulp cells. Trial resin composite liners were made, containing 3wt% fluorides (TiK₂F₆ or NaF). These specimens were immersed in 5ml of cell culture medium supplemented at 37°C for 24 hours. The eluates were used for the experiments. We judged the cytotoxicity of the samples by the cell viability. The original elute solution was serially diluted and then the medium was exchanged for the dilute medium. The cell viability at 1, 2 or 5 days after commencement of re-culturing was calculated. The viability of cells in the eluate from the resin composite liners containing TiK₂F₆ and NaF decreased with time. The cytotoxicity of TiK₂F₆ was weaker than that of NaF at all times.

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In order to further improve the mechanical properties of a metal-resin composite and avoid the problems which were found in the previous metal-resin composite using a 2-paste system, another type of metal-resin composite using a powder-liquid system was developed. In the new system 4-META treatment was carried out at low temperature and DMPT was separated from the 4-META treated particles. The efficacy of this system as well as the effects of 4-META concentration, duration of 4-META treatment (immersion time) and filler content on the flexural properties, working time and setting time were investigated. The flexural strength of the powder-liquid composite was significantly affected by two main factors, immersion time and filler content, and the other properties (flexural modulus, working time and setting time) were by all three main factors. The highest flexural strength of the prepared composite was 91.8MPa, which was higher than that of the 2-paste composite (64.0MPa) by about 43%. This was achieved at a 0.1 ratio of 4-META concentration, 30s immersion time and 94mass% filler content. The working time and setting time ranged between 2.3-13.6min and 4.2-20.1min, respectively, and those of the highest strength composite were 3.0 and 5.2, respectively. The results of the present study indicate that the powder-liquid system is effective to improve the properties of the metal-resin composite.

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The effect of the cavosurface angle of dentin cavities prepared in extracted human molars on the cavity adaptation of a resin composite was evaluated by measuring the gap width between the resin composite and the dentin cavity wall. Cavities with cavosurface angles of 90°, 120°, 135°, or 150° were pretreated with one of two commercial dentin bonding systems or an experimental dentin bonding system. The contraction gap width was measured at both the cavity margin and the section cavity using a light microscope. Complete cavity adaptation was obtained with pretreatment of the experimental groups regardless of the Cavosurface angle. The contraction gap observed at the cavity margin was prevented with the two commercial dentin bonding systems when the cavosurface angle was increased to 150 degrees. A high correlation was observed between the contraction gap width and the proportion of the free surface to the adhesive surface of the resin composite restoration.

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The reinforcement mechanism of dentin mechanical properties by intracanal medicaments was investigated. The dumbbell-shaped specimens were prepared from a collagen sheet, demineralized dentin and organic dissolved dentin. After immersing the specimens in intracanal medicaments (eugenol and formocresol), the tensile test was carried out in 37°C water and the Vickers hardness test was performed. The tensile strengths increased after eugenol and formocresol immersion, especially collagen and organic dissolved dentin after formocresol immersion and demineralized dentin after eugenol immersion. Thus, formocresol immersion might have reinforced the dentin tensile strength by protein coagulation, while eugenol immersion might have reinforced the dentin tensile strength by not only protein coagulation but also chelation with hydroxyapatite. However, the hardness values did not significantly change after intracanal medicament immersion.

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The isothermal age-hardening behaviour of a multi-purpose dental casting gold alloy was investigated by means of hardness testing, X-ray diffraction study, scanning electron microscopic observations and energy dispersive spectroscopy. By ageing of the solution-treated specimen at 400∼500°C, two phases of the Au-rich α₁ phase with an f.c.c. structure and the α₂ phase with an ordered f.c.c. structure based on Pt₃In were transformed into three phases of the α₁ phase, the α₂ phase and the β phase with an ordered f.c.t. structure based on PtZn. Hardening was attributed to the fine nodular precipitation resulting from the formation of the β phase in the α₁ matrix. Softening was due to the coarsening of the fine nodular precipitates as the result of consumption of the α₂ phase.

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The effectiveness of the addition of a photoinitiator into self-etching primer was investigated by measuring the tensile bond strength between a resin composite and dentin or enamel. The addition of camphorquinone to 5M (5wt% MDP -35wt% HEMA aqueous solution) or 30M (30wt% MDP -35wt% HEMA aqueous solution) did not increase the bond strengths of resin composite to dentin or enamel. On the other hand, the bond strength to dentin was increased by the addition of a water-soluble photoinitiator, 2-hydroxy-3-(3, 4-dimethyl-9-oxo-9H-thioxanthen-2-yloxy)-N, N, N-trimethyl-1-propanaminium chloride (QTX) to 5M or 30M. The bond strengths to enamel were not influenced by the addition of QTX to 5M or 30M.

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