Nine types of urethane dimethacrylate(UDMA)monomers which have rigid aromatic(XY-HEMA, XY-HPMA, and XY-HPPM)or saturated cyclohexane rings(IP-HEMA, IP-HPMA, and IP-HPPM)and a flexible hexamethylene chain(HM-HEMA, HM-HPMA, and HM-HPPM)as chemical backbones were synthesized to investigate the relationship between the chemical structure and physical properties of their polymers.The UDMA monomers containing aromatic or cyclohexane rings in their backbone gave good physical properties and lower water sorption to the cured resins.In the case of UDMAs with additional phenoxy groups(the UDMA/triEDMA copolymers)which ranged the concentration of UDMA from30 to 70mol%, showed optimum physical properties such as transverse, compressive and tensile strength, elastic modulus and Knoop hardness.The water sorption values of UDMA/triEDMA copolymers considerably decreased with increasing UDMA concentrations, and those of phenoxy groups added UDMA polymers had low water sorption values.

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The marginal sealing and bond strength of adhesive opaque-resins to the metal frames that were casted with 12% Au-Ag-Pd alloy and Co-Cr alloy respectively, were evaluated.Each opaque resin had strong bond strength when the surface treatment of the metal frame was pretreated.However, the values of bond strength decreased remarkably, and the dye penetration was marked between the opaque and the metal frame after applying thermal cycling for 20, 000 cycles.By using the mechanical retention with the opaque, the retentive strength of the opaque resin increased remarkably and became stable in spite of the exposure to the thermal cycling.Such microretention beads are essential until a stronger and more stable bond strength of the opaque can be obtained.

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This study examined the thinning of palatal area of acrylic resin denture base.After the palatal area was reinforced with carbon-fiber(CF)and aramid-fiber(AF)cloth, it became thin(0.8mm and 0.9mm, respectively).Testing was done by the 4-point bending system, using specimens constrained between the loading steel plates at both molar sides.The palatal area of CF and AF-cloth reinforced denture bases exhibited 50% and 40% thinning, respectively, compared with common resin denture base.The stiffness and the strength of both reinforced denture bases were similar to those of common resin denture base.

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The setting mechanism of self-setting apatite cement was investigated by thermodynamic and X-ray diffraction analyses together with transmission electron microscopy.The thermodynamic analysis of calcium and phosphate in the cement slurry suggested that the solution composition remained for first about ten minutes in equilibrium with dicalcium phosphate dihydrate(DCPD), which is one of the essential components of the self-setting apatite cement.With time the solution composition, however, became undersaturated with respect to this phase and moved towards the solubility line of hydroxyapatite without any apparent equilibrium with other calcium phosphates having solubility lines between those of DCPD and hydroxyapatite.This finding suggests that the thermodynamically most stable phase of hydroxyapatite formed with no involvement of any other precursor phases.X-ray diffraction analysis of solids taken out of the slurry confirmed that hydroxyapatite formed directly as a result of dissolution of the two cement components, DCPD and tetracalcium phosphate.Transmission electron micrography(TEM)indicated that the newly formed hydroxyapatite precipitated predominantly on the basal plane of seed apatite added as a setting accelerator.TEM of sliced specimen of set cement further suggested that the newly formed, needle-like apatite was entangled and intermeshed, resulting in a hard mass as observed with plaster of stones.

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Ag-In alloy cast crowns were removed from the oral cavities of six patients and their tarnish films were analyzed by ESCA.Thickness of the films formed on the alloy surfaces was ranged from 1, 500 to 12, 000Å, and the alloy surface became darker with increasing film thickness.The tarnish films included both In and Zn oxides.The films did not contain sulfides or chlorides of alloy elements but Ag was presented in a metallic state.The Zn oxide in the films was ZnO and In oxide was not In₂O₃ which is the most stable oxide of In.Tarnish of Ag-In alloy in the oral environment arose from the formation of In and Zn oxides on the alloy surface.

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A Ag-Sn-Zn alloy tarnished in the oral cavity was subjected to ESCA analysis.Tarnish film of 5, 000Å thickness was formed on the alloy surface.The film was composed of SnO₂, ZnO and metallic Ag.Neither sulfides nor chloride of the alloy elements was present in the film.Tarnish of the Ag-Sn-Zn alloy in the oral environment was not due to the formation of Ag₂S, but the oxides of non-precious elements, such as Sn and Zn.

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To improve the light transmittance of visible light-cured composite resin, it be desirable that the refractive index of monomer is close to that of filler.The purpose of this study was to develop monomers with refractive indices close to that of silica filler used generally, and polymers with physical properties comparable to those of aromatic dimethacrylate.Four kinds of dimethacrylates with alicyclic skelton, that is, 1, 4-cyclohexanediol dimethacrylate, 1, 4-dimethacryloxymethylene cyclohexane, 2, 2-bis(4-methacryloxy cyclohexyl)propane and 4, 8-dimethacryloxymethylene tricyclo[5.2.1.0^2,6]decane, and two aromatic dimethacrylates polysubstituted by fluorine, that is, 2, 2-bis(4-methacryloxy phenly)hexafluoropropane and 2, 2-bis(4-methacryloxyethoxy phenyl)hexafluoropropane were synthesized.The measurment of refractive indices of these monomers revealed that the introduction of alicyclic skelton instead of aromatic skelton and the fluorine-substitution of dimethacrylate was effective in decreasing the refractive index of the monomer.From the determination of physical properties of these bulk polymers, these synthesized dimethacrylates were found useful for the monomer component of dental light-activated composite resin.

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The influence of load keeping time on 1kgf Vickers hardness(VHN)was tested using bovine mandibular bone, VHN was influenced by the length of load keeping time.Cubic specimens of bovine mandibular bone and bovine dentin were prepared and tested for Vickers hardness and compressive properties in three directions:mesio-distal, upper-lower and bucco-lingual directions.From the results of the test, it was possible to calculate VHN, proportional limit and modulus of elasticity of bovine mandibular bone and bovine dentin.A correlation was observed particularly between VHN and modulus of elasticity in the mesio-distal direction.Hardness and compressive properties of bovine mandibular bone differed according to the directions.Heterogenity on VHN and compressive properties of bovine mandibular bone were analysed quantitatively.

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The present study concerns the trial production of visible light cured denture base resin using cyclophosphazene monomers with a hydrophobic group and a polymerizing group to improve the mechanical properties and lower water sorption.The experimental materials consisted of cyclophosphazene monomer, P₄N₄(CF₃CH₂O)₂[CH₂=C(CH₃)COO(CH₂)₂O]₆[4PN-(TF)₂-(EMA)₆] and 2, 2-Bis[4-(methacryloxy polyethoxy)phenyl]propane[BPE 200]six kinds of monomer compositions were prepared, by changing the mixing ratios of 4PN-(TF)₂-(EMA)₆ and BPE 200 monomers, from 10〜35wt% and 0〜25wt% respectively.Among the 6 visible light cured denture base resins, the composition with preferable mechanical properties and comparatively low water sorption was PMMA and R972, respectively 55 and 10%, to which 20% 4PN-(TF)₂-(EMA)₆ monomer and 15% BPE 200 monomer were mixed. This composition had transverse strength, of 820kg/cm², elastic modulus of 3.2×10⁴kg/cm², and transverse deflection at 15→35 and 15→50N, 0.9 and 1.6mm, respectively. Its hardness was HRS68, water sorption 24.8, solubility 1.1μg/mm³, and contact angle 71%.

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The stress relaxation behavior of human dentin in a compression test was investigated.Cylindrical specimens, 1mm in diameter and 2mm in length, were prepared with a hollow drill made of pure copper.High testing speed of about 250%/min was used to give initial stress, and the stress relaxation test was done in water at test temperatures of 0, 23, 36, and 50℃.Human dentin showed temperature-dependent stress relaxation, and was found to be isotropic with respect to stress relaxation.However variations in stress relaxation with age were observed.The mean percent stress relaxation of dentin was 10〜20%, and this value was about 2〜3 times that of human enamel and 0.2〜0.3 times that of composite resin.Dentin, etched by 30% phospholic acid showed about two-fold stress relaxation.

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Three isomers of methacryloyloxybenzoic acids(MBA)were synthesized to be applied to dental adhesive resin.The tooth-adhesiveness of the self-curing resins containing MBA isomers was evaluated by measurements of their tensile bond strengths.The adhesion promoting mechanism of MBA isomers was examined with respect to their adsorption behaviors onto tooth powders from MMA and by scanning electron microscopy.(SEM)There were appreciable concentrations of MBA in MMA for the o-and m-isomers(2-MBA and 3-MBA, respectively).At 3〜5% of 2-or 3-MBA concentrations, the maximum bond strengths of 14〜15MPa to teeth that were treated with 10% citric acid-3% FeCl₃ solution were obtained by the TBB-O initiated resin.Although the p-isomer(4-MBA)showed very limited solubility to MMA at room temperature, the 1% 4-MBA resin yielded 12.5〜14.5MPa of bond strength to treated teeth.The adhesion promoting effects of MBA isomers were also observed when other polymerization initiating systems such as benzoyl peroxide-tertiary aromatic amine with or without aromatic sulfinate, were employed, and when teeth were not treated.3-MBA may be the best for dental adhesive among the isomers because of its higher solubility to other monomers and superior adhesive stability estimated by long-term immersion and thermocycling tests.SEM revealed that the formation of the resin-infiltrated dentin layer is closely associated with the bond strength to treated dentin, and that MBA promoted the monomer infiltration into demineralized dentin layer.In adsorption to tooth surfaces, MBA was preferentially adsorbed from MMA solution by its carboxyl group with the orientation of the phenyl group being far apart from the tooth surface.The adsorption isotherms suggested that there was competitive adsorption of MBA with MMA to the MBA adsorbed layer.Therefore, the adhesion promoting mechanism of MBA may be as follows:MBA is readily adsorbed to tooth surface from MMA.The MBA adsorbed draws closely the monomers in the adhesive composition toward the tooth surface, or facilitates their hybridization with treated dentin.

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CaO-containing phosphate-bonded investments with various electrical-fused calcia contents were prepared.The setting expansion, the thermal expansion, the X-ray diffraction, the differential thermal analysis and the thermal gravity change were measured.Both the setting and thermal expansions increased due to the addition of CaO above 3%.It is suggested that this effect is due to the chemical reaction to Ca(OH)₂ from CaO.However, this effect decreased with an increase of preservation time of investment powder.

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The object of this work is to determine whether the FRP(fiber reinforced plastics)frame, which was made from visible light cured prepreg, can be clinically used for crown and bridge resin Bonding strength of crown and bridge resins to FRP frame was about 100kgf/cm². Zinc phosphate cement, polycarboxylate cement and glass ionomer cement hardly adhered to the FRP flame.However, bonding strength of resin cement to FRP frame was high and that of Super Bond C & B was about 240kgf/cm². The FRP frame fitted perfectly the stone cast of abutment tooth, and deviation at margin of the stone cast was scarcely observed.The FRP frame had various properties, such as simplicity of use, repair, adjustment and coloring, superior to those of metal frame.Application of the FRP frame crown and bridge resin made opaque resin and retention beads unnecessary These results suggest that the FRP frame can be used clinically for crown and bridge resin.

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NiTi alloy possesses not only unique properties such as shape memory effect and superelasticity but also high damping capacity.In this study, the damping capacity and the shock absorptive characteristic of NiTi alloy were investigated.Specimens of NiTi alloy showed excellent damping capacity and worked very effectively in the shock absorption test as compared to pure Ti, Au-Pt type IV and Co-Cr alloy for dental casting.Furthermore, these two properties were strengthened with heat treatment of 673K, 1800sec.NiTi alloy appears to be useful for the reduction of mechanical stimulation of artificial materials used in medical and dental devices against tissue.

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This study evaluated the usefulness of the square wave current linear polarization resistance(SWCL-method)and the coulostatic method for measurement of the polarization resistance of dental alloys having high corrosion resistances.Polarization resistances of six Ag-Pd binary alloys, Ag, and Pd were measured by using the test solution of saline(0.9% NaCl solution)or an acidic solution(0.9% NaCl and 0.1% HCl, pH2).The SWCL-method was not useful for the measurement of the polarization resistance on the alloys used because it yielded higher values in time constant when saline was used as the test solution, but it could be used for alloys containing less than 33wt% of Pd when an acidic solution was used.The coulostatic method was applicable to all the alloys in both the two solutions.The results suggested that the coulostatic method would be useful in monitoring the corrosion rates of the Ag-based alloys, since the polarization resistance is converted into the corrosion rate by using the constank K value, which is considered to be constant in a corrosion system.

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The effects of casting temperature were studied on the surface aspects and casting porosities of Ag-Pd-Au alloy cast crown.The alloy was centrifugally cast at two different temperatures, 1, 000℃ and 1, 200℃.These temperatures were selected on the basis of the casting temperature range determined by the molten alloy appearance in the previous study.The crown surface was entirely covered with dark copper and zinc oxides, and no chages were found in surface appearance by altering the casting temperature or adding flux.On the other hand, the oxides on the button surface were apparently decreased by the use of the flux only when the alloy was cast at 1, 000℃.The castings made at 1, 200℃ were characterized by thicker oxide laxers on the upper surface of the button, extensive burning of the investment on the bottom surface of the button, and marked casting porosities on the occlusal subsurface of the crown.The flux was no more effective for protecting the alloy from oxidation at 1, 200℃, although the porosities were considerably reduced.

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The reactivity of molten titanium with various refractory oxides(SiO₂, Al₂O₃, MgO, CaO, ZrO₂)was investigated experimentally.Titanium castings were obtained using the investments composed purely of refractory oxides and without any additional components except water or sols or MMA as temporary binder, which get decomposed away with burning.The surface of the titanium castings was observed by optical and electron microscopy.Elemental analysis was done using ESCA.The surface products were identified using the thin foil X-ray diffaction method(TFD).Of thess refractory oxides, SiO₂ was the most reactive with titanium, followed by Al₂O₃.The reaction products included Ti-Si, Ti-Al compounds other than Ti oxides.MgO, CaO, ZrO₂ show very little reaction and principal surface products were Ti oxides.Reactivity, reaction layer thickness and reaction products were determined and their mechanism was discussed.

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As reported previously, the thermal expansion of a new dental investment, which was composed of AlPO₄(berlinite)refractory and phosphate binder, was no more than 7%. However, it is necessary to control the amount of thermal expansion for practical use.New dental investments for dental casting were prepared by mixing SiO₂ refractorys with AlPO₄(berlinite) refractory(5〜30wt%) and phosphate binder(14wt%) to control overall thermal expansion.Adaptability of castings made of various types of dental alloys was examined with MOD metal mold by only thermal expansion techniques.The relation between the distortion of castings and the setting expansion were examined.The properties of the new dental investments were compared with those of commercially available phosphate bonded investment.The rapid increase in the linear expansion of the new dental investment occurred on heating both at the temperatures of α-β inversion of quartz, cristobalite and berlinite and at the temperature of transion of β-berlinite from β-cristalphite.The more SiO₂ blended with AlPO₄, the less was the resulting thermal expansion.In this manner, the thermal expansion was varied within a range of approximately 1.5 to 3.0 at 700 or 800℃.The casting shrinkage of dental alloy could be compensated for because the overall thermal expansion could be controlled by changing the ratio of components.It was found that the less the setting expansion, the less was the distortion of castings from the point of defined distortion amount.Furthermore, the coefficient of correlation between the setting expansion and the distortion of castings was 0.86.Such physical properties of the new dental investments as compressive strength, setting time and setting temperature were no less or better than those of the available phosphate bonded investment.

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A new database system of literatures on dental materials and devices was developed by the Committee for the Database, the Japanese Society for Dental Materials and Devices, with the cooperation of the members.The constitution of the data stored in the database and its on-line retrieval system were interpreted.

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