Plasma-spray coated hydroxyapatite layer is often applied to sintered ceramic implants to increase implant porosity.We conducted this study to investigate the variation in degree of porosity achieved through the plasma-spray coating technique.We added 30%, 40%, and 50% salt to a powder mixture of 80% hydroxyapatite and 20% aluminum oxide, and applied this mixture through plasma-spray coating.Finally we flushed the surface with water.We investigated the relationships between the amount of salt in the coated layer and its bonding strength, surface roughness, and diffraction pattern.The salt that we mixed with the coated layer dissolved in the water, leaving the coated layer surface very porous.The mechanical properties of the porous coated layer did not differ significantly from those of a normal coated layer.The roughness of the surface increased with the increased in the amount of salt mixed with the hydroxyapatite-aluminum oxide mixture.Negligible decomposition of hydroxyapatite due to salt was observed as judged from the X-ray diffraction pattern.Histological examination revealed that the porous extended deep into the layer.

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In order to investigate odors associated with used dentures, we conducted experiments to determine the odor intensity of heat-curing, microwave-curing, and self-curing (pour type) denture resins as polymerized pieces, and in their powder and liquid forms.In addition to these resins, we also investigated light-curing and compression molding materials.To measure the odor intensity of these materials, we used an odor measuring apparatus that can be operated in an ozone based atmosphere, "ALABASTER" (B&H LABO.Co., Ltd., Kurume, Japan), using a semi-conductor sensor(SnO₂).We also performed gas chromatograph and gas chromatographmass spectrometer analyses of the heat curing resins.The results are given as the following:1.There was significant difference among the odor concentration values of the resin powders, but there was no significant difference among the values of the resin liquid and the polymerized pieces of heat-curing denture resins.2.The values of the polymerized pieces were lower than those of the resin powders and liquids.3.The polyethersulphone denture base showed the lowest value of the resin polymers.4.MMA and EDMA were found to be present in all samples of heat-curing resins as determined by gas chromatograph and gas chromatograph-mass spectrometer testing.Toluene and ethyleneglycol mono methylether were found only in one sample.

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An aqueous solution, containing aminoacid derivatives and 2-hydroxyethyl methacrylate(HEMA), has been used as a surfactant to reinforcing the bonding strength between commercial bonding agent and tooth substance, and its bonding mechanism has been determined.In the present investigation, such a high tensile bond strength as 170 or 136kgf/cm² to bovine dentin or enamel was obtained with an experimental bonding agent, containing an aminoacid derivative, N, O-dimethacryloyl tyrosine(DMTY).The findings revealed the excellent property of the surfactant, N-methacryloyl α-alanine(an aminoacid derivative:MAL)-HEMA solution, the affinity to tooth substance of the agent containing DMTY and the favorable strength of the layer of bonding agent.Quantitative analysis of the amount of Ca and P, dissolved from bovine dentin, revealed that aminoacid derivatives hardly dissolve hydroxyapatite in comparison with other traditional etching agents.

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β-tricalcium phosphate(β-TCP)was synthesized in an aqueous or dry system.Although in the aqueous system the synthesis was done with various(Ca+Mg)/P molar ratios at 40℃ or 80℃ and various pH, β-TCP was not detected.However, after 1-month incubation of Mg-containing amorphous in potassium acatate buffer solution, β-TCP was revealed.Furthermore, after the ignition of this Mg-containing amorphous, β-TCP was detected at 200℃.On the other hand, in a dry system well-crystallized β-TCP was formed by heating the stoichiometrical mixture of CaHPO₄・2H₂O and CaCO₃ at 2:1 molar ratio at 1100℃.The computer graphics of β-TCP demonstrated that β-TCP has an unstable complex structure due to 0.5 probability of Ca²⁺ions(Ca*)in straight[PO₄-Ca*-Ca-PO₄-Ca*-Ca]column and[PO₄-Ca-Ca-Ca-PO₄]zig-zag chain.

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The optimum photoinitiator composition, and the conversion after polymerization, of visible light-cured resins, were determined.As monomers, synthesized cyclophosphazene monomer P₄N₄(CF₃CH₂O)₁[CH₂=C(CH₃)COOCH₂CH₂O]₇[4PN-(TF)₁-(EMA)₇]and commercial Tri-EDMA were prepared for the visible light-cured resins by changing the amount of photoinitiators.As photosensitizers, comphorquinone(CQ)and dibenzoyl(DB)were used.As a reducing agent, methacryloxyethyl-p-dimethylaminobenzoate was used.Eighteenth trial resins were investigated by means of a fourier transform infrared spectrophotometer(Shimadzu FT-IR 4300)by the liquid film method.The infrared absorbance measurements were made before irradiation and chronologically repeated after the resins had been polymerized by irradiation.The quantities of remaining double bonds(RDB)were determined and the data expressed as percentages of the total amount of double bonds in the unirradiated resins.The RDB for 4PN-(TF)₁-(EMA)₇ resins showed 56〜78% at 5min after the start of irradiation, 47〜71% at 1 day.The RDB for Tri-EDMA resins showed 27〜63% at 5 min after the start of irradiation, 15〜47% at 1 day.The RDB significantly decreased with the increase in the mixed amount of CQ for 4PN-(TF)₁-(EMA)₇ resins, and that of DB for Tri-EDMA resins.

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A new gypsum-bonded investment for high temperature casting was developed.The investments composed of gypsum and several kinds of refractory materials were examined by thermogravimetric analysis, differential thermal analysis, thermal expansion measurement, casting test and some mechanical properties test.Thermal analysis revealed that thermal decomposition temperature of gypsum mixed with refractory material, was lower than that of gypsum alone, and that the kind of refractory material affected the decomposition temperature.The refractory materials tested in this study were arranged in the order of thermal decomposition temperature;SiO₂, Al₂O₃, CaSiO₃, MgO, ZrO₂, CaO and ZnO.This order was roughly in agreement with the basic degree of refractory materials.To prevent the drop in decomposition temperature, used by carbon, the additive calcium oxalate was more effective than oxalic acid.When alumina or zirconia was used as a refractory material of gypsum-bonded investment, thermal expansion of the investment increased significantly at the temperature above 1, 200℃.Co-Cr alloy, of which melting temperature is 1, 399℃, could be cast soundly in the casting mold made with gypsum-bonded zirconia or zincoxide investment.Thermal decomposition area of this mold tested by phenolphthalein, was limited to the periphery of inner surface of casting mold.

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The measuring errors and dependences on loading condition such as load, load-holding time and loading speed, were examined for Micro-Vickers hardness testing.The distribution of microhardness of human teeth especially cementum which was difficult to measure in the past, was determined.Micro-Vickers hardness of human dentin depends on load, load-holding time and loading speed.The measuring apparatus should be chosen strictly, because the measuring error increases with a lighter load.The distribution of microhardness of human cementum could be measured by this method of microhardness test.The microhardnesses of peritubular dentin and intertubular dentin could be measured using a supermicro load, 0.2g.

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Heat treatment of titanium from 300 to 1, 200℃ under air, in vacuo and under oxygen partial pressure was done for solution hardening by oxygen.The surface oxide film was stable up to 800〜900℃.At a higher temperature oxidation showed the different phenomena.The surface oxide layer was formed by the single step heat treatment even under vacuum at a lower temperature(<800℃).By the double step heat treatment, where the oxide film was dissolved and absorbed into metal by the temporary heating to a higher temperature(>900℃), and oxidation process was followed at a lower temperature, more oxygen was dissolved into titanium.By the further homogenizing anneal after oxidation, the surface oxide film disappeared through the dissolution into metal and the metallic brilliance reappeared.By measurement of the micro-Vickers hardness along the depth from surface in the specimen cross-section, the diffusion range of oxygen could be confirmed as the increase of the hardening layer thickness.The experimentally obtained value of hardening layer thickness was quantitatively in good accordance with that calculated from the activation energy of ox gen diffusion in titanium.Whether oxygen contributes to the formation of oxide layer or it becomes solute atoms in metal depends on the balance between the reactivity of the gas oxygen to surface oxide and the dissolution rate of oxygen from layer to metal.When there exists a stable oxide layer at the surface, the solution and diffusion of oxygen into metal is blocked.These models could explain the phenomena well.

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The applicability of Ti-6Al-4V alloy to a prefabricated post was evaluated.The mechanical properties and compatibility with cast metal core were examined in comparison with those of some commercially available prefabricated posts of pure Ti, Ni-Cr alloy and 18-8 stainless steel.The Ti-6Al-4V alloy showed better applicability in terms of mechanical properties obtained from tensile, bending and hardness tests as a post material.It showed a significant decrease in elongation when heated to 1, 000℃, but little change in tensile strength as compared with the Ni-Cr alloy and stainless steel.The castability of Ni-Cr and Ag alloy core onto the Ti-6Al-4V tapered, serrated post was excellent as it was onto the pure Ti post.These findings indicate that the Ti-6Al-4V alloy is useful for a prefabricated post with cast metal core.

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The previous report demonstrated the superlority of Ti-6Al-4V in mechanical properties for a prefabricated post.A comparative study was carried out on toxicity to culture L-929 cells for pure Ti, Ti-6Al-4V and conventional Ni-Cr and 18-8 stainless steel posts.In the 24-hr immersion tests, dissolution of the constituent elements was accelerated from Ni-Cr and 18-8 stainless steel posts by casting the Ag alloy core onto them, resulting in induction of their cytotoxicity.Pure Ti and Ti-6Al-4V, on the other hand, could minimize the cytotoxicity even with the Ag alloy cast core, indicating that they would be excellent materials as the prefabricated posts also in terms of biocompatibility.

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The maxillary and mandibular tooth model were set on the articulator with the maxillary model turned over, and the three dimensional shape of the tooth models were measured by the system composed of a laser displacement meter with double sensor and a computer controlled tooth model scanning machine.The elementary simulation of the occlusion was carried out.The protrusive movement of mandible was simulated using the data of left 5〜7 upper and lower molar.By considering the retrusive and rising movements of maxilla along the condylar path, we could simulate the reduction in the amount of excessive bite.In the case of lateral mandibular movement, not only the rotational movement of maxilla setting one condyle at the central position of movement, but the rising movement along the another condyle was taken into account.Accordingly, the disappearance in the occlusal contact with the 7 molars by the right lateral movement, and, on the contrary, the increase in bite by the left lateral movement could be simulated.The opening and retrusive movements could be set up arbitrary, and the successive occlusal movements displayed by the computer graphics.Furthermore, the simulation with full teeth was carried out by maxillary and mandibular model.The data were measured with the hinge axis to be main measuring axis.With the closing movement, a slight occlusal contact was observed on the right 6 and 7 molars, and the successive increase in occlusion of buccal cusp of mandibular molar with central fossa of maxillary molar was simulated.In the present paper, the average value articulator was used.Further assumptive occlusion can be simulated, because the parameters such as the tilting angle of condyle path and position of condyle can be changed arbitrary by the computer program according to the articulator situated or the physiologic morphology.

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The setting reaction of the die stone surface was investigated by SEM observation and X-ray diffraction analysis when the stone was poured into the alginate hydrocolloid impressions which were pretreated with the 5 to 40% concentrated calcium chloride solutions.The growth of dihydrate salt was markedly accelerated at the stone surface set on the alginate impressions pretreated with calcium chloride solutions, whereas the hemihydrate salt remained to a considerable extent when the impressions were not pretreated or pretreated with the conventional fixing solution, 2% zinc sulphate solution.The mode of the dihydrate crystal growth on the modified alginate impression surface was different from that on the addition silicone impression surface.The crystal growth also varied with the concentration and the pretreatment time of calcium chloride solution, and the brand of alginate hydrocolloid impression material also.In conclusion the concentrated calcium chloride solution was very effective as a fixing solution to improve the surface quality of the die stone poured into the alginate hydrocolloid impressions.

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Recently, Bis-GMA based microfiller composite resins are often used for restoration of the dental crown.However, the mechanical properties of these resins have been indicated to be inferior to those of conventional filler composite resins.The role of Bis-GMA in the base comonomer, was examined using a torsion pendulum viscoelastometer, and the effects of the filler on the dynamic shear modulus of composite resins were discussed.The increase of the Bis-GMA elevated the dynamic shear modulus at about room temperature.However, this increase brought about marked deterioration of the dynamic shear modulus at a temperature higher than 80℃.On the other hand, the microfiller was not particularly effective for improving the dynamic shear modulus.

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