This study atlempted to develop a resin cement with high adhesive and compressive strength and low disintegration.Therefore, adhesive cyclophosphazene monomer was synthesized.Four kinds of cements were prepared the using the synthesized monomer, then the tensile adhesive strength between cement and bovine dentin or three kinds of dentin alloy as well as the compressive strength disintegration were measured.Among four kinds of cements, the best results for adhesive strength, compressive strength and disinitegration were obtained when the liquid composition consisted of 60wt% monomer, 38wt% HEMA and 2wt% polyacrylic acid.The adhesive strength between the synthesized monomer and bovine enamel and bovine dentin was 5.2MPa and 3.7MPa, respectively.It was 38.3MPa for Co-Cr alloy, 27.9MPa for Ag-Pd-Au alloy, 24.8MPa for 18 Karat gold alloy.Compressive strength and disintegration were 210MPa and 0.23%, respectively.

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The rate of dissolution of sintered carbonate apatites was estimated in 10mM acetic acid solutions at 37℃ at a constant pH of 5.0.When compared at the same sintering temperature, the rate of dissolution increased with increased concentrations of carbonate initially present, indicating that the presence of carbonate plays an important role in the dissolution of sintered specimens.With the same sample, however, the dissolution rate decreased as the sintering temperature increased.For example, the rate of dissolution of the sintered specimen, which was prepared by sintering an apatite sample initially containing about 12wt% carbonate at 750℃, was nearly one-fifth that of the non-sintered specimen and about one-third that of a non-sintered specimen of deproteinated bone.Comparison of carbonate apatite sintered at 750℃ and a carbonate-free apatite sintered at 1, 200℃ showed that the dissolution rate of the former was approximately four times as great as that of the latter.This finding clearly suggests that the sintered carbonate apatite is much more soluble than sintered carbonate-free apatite, indicating that carbonate apatite is more useful as a bone substitute material.

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This study investigated the electrochemical absorption of a functional monomer which showed adhesion to dental alloys to obtain firm adhesion between dental alloys and methacrylate resin.An alloy surface treated electrochemically with a functional monomer:β-methacryloyl oxyethyl hydrogen succinate(SA)was analyzed with IR and the shear bond strength of self-curing methacrylate resin to dental alloys exposed to various treatment conditions was measured.A functional monomer was electrodeposited on the alloy surface and its carboxylate ion formed an ionic bond, but its methacryloyl group did not react.Maximal bond strengths of 9.1, 11.0 and 8.0MPa were obtained for 12% Au-Ag-Pd alloy, Co-Cr alloy and pure titanium, respectively.It was suggested that appropriate treatment conditions(concentration and current)to increase bond strength varied with the type of dental alloy.

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A gypsum powder was mixed with 0.5, 1 and 2% solutions of accelerators(ZnSO_4 and K_2SO_4), and poured into agar, agar/alginate combined and alginate impressions.Surface roughness(Ra)of the stone models measured to evaluate the compatibility of gypsum with the combined impressions.For the agar impression, the effects of accelerators altered in the agar brand.The Ra decreased markedly with increses in the concentrations of accelerators for one brand which had poor compatibility with gypsum mixed with water.The accelerators were less effective in reducing the Ra of specimens from combined or alginate impressions.A significant linear correlation was noted between the setting time and the Ra in four of ten combinations.Based on these results, it is recommended that the mixing of gypsum with 1〜2% ZnSO_4 solutions as one of method of improving the compatibility of gypsum with the agar/alginate combined impression.

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Using a parallel link mechanism which has a fixed point in the mouth, a preparation support tool to keep the axis of the turbine hand piece parallel was developed.This mechanism assists for students in learning the correct preparation technique.In the present study, two supervising dentists with career of two years and more than ten years respectively, prepared upper and lower resin model molanr teeth using this mechanism, and the taper angle and axis parallelity in the prepared die were examined.This mechanism was helpful for the correct preparation, and the prepared taper angles were reduced to about 10°〜14°, and tilt angle between the axes was within 2°, and their standard deviations also decreased.To compare these results with those of free hand preparation, 24 experimental items such as taper angles were checked by paired t-test.Nine items prepared by the dentist with a two-years career, and 14items by the dentist with more than ten years experience were two-years career, and 14 items by the dentist with more than ten years experience were concluded to differ significantly compared with those by free hand preparation.

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Automatic control of porcelain wetness which is indispensable to computerize porcelain forming was studied.A method of quantification of wetness using image processing was applied to the experimental system.Automatic control of wetness was realized by repeating water supply and condensation until the wetness index increased above the desired value.The water supply could easily become excessive or inadequate following slight changes in the quantity of porcelain powder or evaporation speed when the supply was not automatically controlled.With automatic control, the wetness of formed porcelain could be maintained within an acceptable range.Movement of the work piece caused decreases in the wetness index and excessive water supply succeedingly, but the influence was reduced by refocusing the lens of the camera with every move.From the results of automatic forming, it was found that the system could be so improved as to be able to form well at a lower wetness index.The control of porcelain wetness should be subdivided into overall wetness and local wetness at the site where the porcelain powder is added.

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Various heat treatments were carried out on a commercial Ag-Pd-Cu-Au dental alloy.Static three-point bending fracture toughness tests were then carried out on heat treated alloys.The influence of microstructure with changing heat treatment condition on static fracture characteristics were investigated based on the test results.The static fracture toughness values increase with increases in the solutionizing temperature except for a solutionizing temperature of 1123K.The increase in the static fracture toughness values is considered to be due to solid-solution strengthening where the α_1 phase dissolves into α_2 phase.The static fracture toughness values tend to increase with increases in the solutionizing temperature except for a solutionizing temperature of 1123K in aged materials.However, in cases of solutionizing at 1023 and 1123K followed by aging at 673K, the static fracture toughness values decreased remarkably mainly due to the precipitated β phase which forms a fracture site.The heat treatment condition where the solutionizing temperature is 1073K is judged to be superior when the static facture characteristics are taken into account.The heat treatment process where air cooling is adopted after solutionizing is better because cooling is comparatively similar to as-cast conditions and the aging process can be omitted.

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Thiirane monomers, 2, 3-epithiopropyl methacrylate(EP1MA), 4, 5-epithiopentyl methacrylate(EP3MA), 9, 10-epithiodecyl methacrylate(EP8MA)and 10, 11-epithioundecyl methacrylate(EP9MA), were used to promote bonding of adhesive resins to precious metal alloys.Twelve MMA-PMMA/TBBO type resins were prepared by dissolving a thiirane monomer in MMA monomer liquid at concentrations of 0.1, 0.5 and 1.0mol%.Two precious metal alloy specimens were polished to a mirror-like finish and butt-jointed together with experimental resin.Then, tensile bond strengths were measured after 2, 000 thermal cyclings.The incorporation of thiirane monomer into resin significantly enhanced the bond strength, which was generally increased in the order of EP1MA<EP3MA<EP9MA≦EP8MA.The experimental resin, in most cases, showed the highest bond strength at 1.0mol% of thiirane.It was demonstrated that the experimental resin with 1.0mol% EP8MA provided excellent bond strengths comparable to those obtained by surface treatment with 1.0mol% EP8MA.

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