Cell recovery of four cell lines[L-929 cells, HEp-2 cells, Gin-1 cells and the cells from human dental pulp tissues(Hp cells)]was examined after exposure to four zinc phosphate cements, five polycarboxylate cements, three glass ionomer cements, five resin based cements and one zinc oxide-eugenol・EBA cement.Phosphate cements, glass ionomer cements and zinc oxide-eugenol・EBA cement were markedly cytotoxic to the four cell lines 3 hours and 24 hours after mixing.Polycarboxylate cements considerably inhibited cell recovery of the three types of cells except Hp cells even 24 hours after mixing, compared to the gradual recovery of Hp cells after mixing.Two of the resin based cements inhibited cell recovery, while the three others allowed moderate cell recovery.The pH values of the medium used for the experiments was 6.6-6.8 for phosphate cements, glass ionomer cements and zinc oxide-eugenol・EBA cements Polycarboxylate cements had no effect on the pH.On the other hand, in resin based cements the pH was shifted from acidic to basic.The solubility of the materials used was, in decreasing order:glass ionomer cements, zinc oxide-eugenol・EBA cement and one of the resin based cements, polycarboxylate cements, phosphate cements and another resin based cement, and the other three of resin based cements(lowest).The difference in cell recovery was considered to be due to composition and solubility of the materials.

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Fe-containing hydroxyapatites and fluoridated hydroxyapatites were synthesized at 80℃ and pH7.4.Fe-containing hydroxyapatites became poorly crystallized with the increase of Fe²⁺ ions in the solution and a- and c-axis dimensions seemed to decrease slightly.The apparent solubility of Fe-containing hydroxyapatites decreased greatly with the increase of iron content in spite of the decrease in crystallinity.Fe-containing fluoridated apaties were less well crystallized than Fe-free fluoridated apatites.The Fe²⁺ uptake of fluoridated apatites was independent of fluoride concentration in the solution.a-Axis dimensions of Fe-containing fluoridated apatites decreased with the degree of fluoridation in addition to the decrease related to the substitution of Fe²⁺ ions.The apparent solubility of Fe-containing fluoridated apatites decreased more than that of Fe-free fluoridated apatites especially at a low fluoride content.

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The direct tensile test of composite resins using the specimen with the gauge length 10mm has been developed by authors.In this study smaller specimens with the gauge length 5mm and 2mm were also investigated.As the gauge length became smaller, tensile properties such as the proportional limit, the proof stress, and the tensile strength showed the tendency to become higher.The effect of strain rate on the tensile properties appeared clearly when using the specimen with the gauge length 2mm.The small specimen was found to have many advantages for the preparation, the cost of material and the handling during the tensile test.

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The zirconia investments with calcia were studied of the compressive strength, setting expansion, thermal expansion, total expansion, thermogravitometry, differential thermal analysis on fabrication method, concentration, particle size of zirconia, calcia and mixing liquid.Addition of calcia caused the change from contraction to expansion in setting expansion.The optimum concentration of calcia was determined to be 10mol% as judged from total expansion, strength and operability.

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The bending fatigue test of crown and bridge resin facing metal frame was carried out under a scanning electron microscope, and the fracture and propergation behavior of junction was studied.The resin facing metal frame with retention beads had a static breaking stress of about 100kgf/mm², .The resinfacing metal frame, when bonded with adhesive, had the stress of about 36kgf/mm².The specimens with retention beads and bonded with adhesive were not destroyed at cycles of 10⁶ under the bending fatigue stress of below 40% and 50% of the static breaking stress, respectively.Marginal micro gaps between resin and metal frame with retention beads were observed before the fatigue test, and were increased with the number of cycles.Then fracture of the specimen occurred from the resin of the retention beads side.In the specimen bonded with adhesive, marginal micro gaps between resin and metal frame were observed during the fatigue test, and the partially cohesive fracture occurred.

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Seven 2-thiobarbituric acid derivatives with methyl substituents were synthesized.Experimental visible-light curing resins were prepared using these compounds as a reducing agent in the dl-camphorquinone(CQ)-reducing agent initiator system.The effects of methyl substitution for thiobarbituric acid on initiation behavior of CQ-thiobarbituric acid initiator system were examined by analysis of polymerization of triethylene glycol dimethacrylate(3G)in DSC and depth of cure.The solubility of thiobarbituric acid derivatives in 3G was markedly changed by the introduction of the methyl group.Although the methyl group substitution at position 1(3)in thiobarbituric acid improved the solubility of the acid in 3G, it did not enhance the initiation ability.Maximum exothermic rate, time at maximum exothermic peak, amount of insufficiently polymerized layer and depth of cure were significantly improved by the introduction of one methyl group at the position 5.Thus the initiation ability was enhanced by the substitution.However, the introduction of two methyl groups at position 5 did not promote polymerization, but the inhibitory effect became apparent as the concentration of the reducing agent was increased.

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A centrifugal barrel finishing apparatus with a variable turn table rotational speed(250〜1, 000rpm)was newly developed and barrel finishing of Ni-Cr casting plates(10×10×2mm)was performed using alumina base chips.When using the sample with a mirror face the amount of polishing and the surface roughness increased and the surface gloss decreased with the increase in rotation speed.A high rotational speed was useful for coarse polishing and low rotational speed was useful for fine polishing.The continuous barrel polishing was trially performed using the sample prepared by the carborundum wheel under variable rotational speed.Automatic polishing to fine polishing could be done using this apparatus.

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Mechanical properties and curing depth of light-cured composite resins based on five types of urethane tetramethacrylate(UTeMA;IP-4M, XY-4M, MC-4M, HM-4M and TM-4M)were investigated, and compared them with those of UDMA-based composite resins Composites based on UTeMA monomers containing a aromatic or cyclohexane ring in their chemical structure(IP-4M, XY-4M and MC-4M)showed a relatively rigid properties than those based on aliphatic UTeMA(HM-4M and TM-4M).The composite resins based on XY-4M monomer showed a curing depth and transmission coefficient superior to the other composite resins UTeMA-based composites showed a significantly higher rigid properties than UDMA-based composites, while their rigidity did not improve the flexural strength.

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