The influence of thermal cycling and water immersion on the mechanical properties of posterior restorative composite was resins investigated.Six commercially available dental composites were chosen, and after storing samples in distilled water at 37℃ for 24hours, a thermal cycling test(37℃, 60℃, 37℃, 4℃)was performed at 2, 000, 10, 000 and 20, 000cycles for compressive samples and 10, 000cycles for transverse and diametral samples.Deterioration by thermal cycling was observed on the compressive yield strength of CP, P10, BF and MJ and transverse strength of CP, P10, IM and PF.

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Four composite resins, polished by different methods, were tested for staining and/or penetration by staining solution.Surface set cured against slide glass(smooth surface), white point-polished surface and finishing surface were prepared for each materials, and immersed in 0.2% Fuchsin solution at 37℃ for 60 days.The staining was evaluated by measuring of Adams' color difference(ΔE)before and after 3, 10, 20, 30, 40, 50, 60 days of immersion period, respectively.After 60 days, specimens were sectioned thinly and longitudinally.They were observed with a polorization microscope, and the thickness of the staining layer was measured.Finishing surface had a lower ΔE value than smooth and white point-polished surface.The thickness of the staining layer of finishing surface was significantly thinner than that of smooth and white point-polished surfaces(P<0.01).The ΔE value of every surfaces showed some correlation with the thickness of the staining layer.Microrest had a lower ΔE value and lower thickness in staining layer than the other resins.

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Fluoridated apatites were synthesized at a wide range of calcium-phosphate molar ratios, (Ca/P)_f, at 80℃ and pH7.4, and at a constant calcium-fluoride feed ratio, (Ca/F)_f.In spite of the constant(Ca/F)_f of 5, F^- uptake of fluoridated apatites synthesized at(Ca/P)_f below 1.67 was strongly inhibited.The a-axis dimension, crystallinity and solubility of these fluoridated apatites varied with fluoride content in roughly the same manner as those with various degrees of fluoridation(X=0〜1), synthesized at a constant(Ca/P)_f of 1.67.These results suggest that the physicochemical properties of fluoridated apatites are more strongly affected by fluoride content than other ions.

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As part of a study on adhesion of dental alloys by MMA-TBB type resins, testing methods of adhesive strength measurement and surface treatments of various alloys were investigated.Aluminum and Tin showed excellent adhesive durability from the results of adhesive experiments utilizing elemental metals.The thermal cycling test, a severe testing method than the long-term immersion test, proved to be effective to evaluate adhesive durability.Sn plating for Type IV gold and Au-Ag-Pd alloys and Iron(III)chloride acetone solution treatment for Ni-Cr alloy were suitable methods for alloy surface treatments.

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This study examined the surface roughness and the convergence angle of epoxy resin molds and measured the space of bridges.This epoxy resin mold found to be a suitable material for future study.It was concluded that the operation of the repressing margin parts of the bridge must be done at wax-up time.When measured without cements, the decrease in space was negatively correlated to the convergence angle.

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The author investigated the influence of changes in the convergence angle and temperature on the glass slab on the quantity of vertical discrepancy of the cemented bridges.The apparatus and metal mold used were capable of varying the convergence angle of both a premolar and a molar from 4degrees to 14degrees at increments of 2degrees.When measured with cements, the film thickness did not decrease except at convergence angles between 8 and 10degrees.The film thickness of bridges was influenced by the convergence angle of molar much more than of premolar.When the convergence angle of premolar increased and the molar decreased, the slant of the bridges was distinctly observed, but when the condition was reversed, such phenomenon was not seen.As for the consistency and the film thickness test based on ADA specification No.8, no marked decrease of the consistency of the film thickness was observed with decreases in temperature.However, by shortening the operation time to 2 minutes which included mixing time, both the consistency and the film thickness decreased.Also, film thickness of bridges decreased markedly with decreases of temperature.It is suitable the findings indicate that the mixing temperature should be 13℃ to 15℃ with 60% relative humidity.

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We applied the Raman microprobe technique to analyze the chemical components at the interface layer between dentine and resin.A thin layer, about 5μm under interface, where both resin components and dentine components were present.These finding strongly suggest that resin reinforced dentine.In addition, 4-META or 4-MET appear to be more highly concentrated in this layer than in the resin side of the interface.

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To monitor the biological action at the membrane level induced by photosensitizing agents, we studied the thermodynamic changes in the phase transition temperature(T), enthalpy(ΔH), entropy(ΔS), and H(height)/HHW(half-height width)of dimyristoylphosphatidylcholine liposomes induced by camphorquinone(CQ), benzil(BZ), 9-fluorenone(9F), benzoin methyl ether, azobisisobutyronitrile, acridine orange(AO), anthracene(AN), and neutral red(NR)using differential scanning calorimetry.For photoinitiators 9F+DM(N, N-dimethylaminoethyl methacrylate)and BZ+DM caused large changes in the T and ΔH(T shift to a low temperature)and a large decrease in the ΔH, whereas the changes of CQ+DM were smaller than those of the 9F and BZ systems.Action of aromatic ketones(9F, BZ)to liposomes was higher than that of aliphatic ketones(CQ).The T of AO and NR, which was a small decrease in the ΔH, was shifted to a higher temperature(1〜3℃).Also, AN, AO, NR caused large changes in the ΔH and ΔS at 30℃, pH10 when oxygen was present in their systems during photosensitization.Since DMPC does not have double bonds in its molecules, lipid peroxidation does not occur.Therefore, it is suggested that the large interaction of photosensitizing agents with liposomes may be due to the excited charge-transfer complexes between photosensitizer(CQ, BZ and 9F)and reducing agents(DM), and between photosensitizing agents(AN, AO, NR)and oxygen.

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Inlay waxes were prepared for the use in complex castings, which have both the male portion of the pattern and the male portion of the die.The male portion of the wax pattern requires sufficient shrinkage to allow the layer of cement between the castings and the cavity.On the other hand, the shrinkage of the wax pattern at the male portion of the die is restricted by stress relaxation of the wax.The main component was paraffin with a high melting point and the others were carnauba wax, dammar and beeswax.Physical properties such as thermal expansion, flow and stress relaxation of these prepared waxes were investigated.The inlay wax having large shrinkage at the male portion of the pattern could be formulated using paraffin with a high melting point but without isoparaffin.In this case, it was necessary to add small amounts of paraffin with a low melting point in order to reduce the operational difficulty.Small amounts of carnauba wax, which restrict stress relaxation and suitable amounts of other ingredients, should be added to minimize the shrinkage of the wax pattern at the male portion of the die.

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We have been studying adhesive resins to dentin by using new methacrylates with hydrophobic and hydrophilic groups such as 4-methacryloxyethyl trimellitate anhydride(4-META).During studies on adhesion mechanism of a 4-META/MMA-TBB resin to dentin, it was found that the denaturation of dentinal collagen during acid etching decreased the bond strength to 6MPa, and that the preservation of the higher structure of the protain by application of glutaraldehyde or FeCl₃ in the pretreatment for the bonding was essential to obtain higher bond strength(11〜18MPa)to dentin.A new bonding agent without TBB was developed in this study.It consists of two components, one is 2wt% 4-META in a monomer mixture of 20% HEMA and 80% MMA containing 0.5wt% BPO, and the other is 2wt% p-toluenesulfinic acid sodium salt and 5% glutaraldehyde in ethanol.The tensile bond strength treated with 10-3 for 30 sec, 0.5M EDTA 2Na for 60 sec or 65% phosphoric acid for 30 sec were 13, 9 or 19MPa respectively.The treated dentin was first applied to the bonding system, and then joined to a PMMA rod with conventional BPO-amine self-curing resin.

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In our on going study of adhesion to bovine tooth substrates with 4-META/MMA-TBB resin, two painting techniques were examined to find an optimal treatment prior to bonding to EDTA pretreated tooth surface.One was the currently used single-painting technique, in which liquid monomers of the resin are applied once to pretreated tooth surface prior to bonding with the resin paste.The second was triple-painting technique, in which liquid monomers of the resin were applied to pretreated tooth surface three times prior to bonding with the resin paste.After each succeeding liquid monomers application, the prepared tooth surface becomes drier.A 1-min pretreatment with 0.3M EDTA・2Na-0.2M EDTA・Fe・Na(pH7.4)was found to be relatively effective in removing the smeared layer.Good tensile bond strengths enamel 13MPa and dentin 12MPa were obtained when the triple-painting technique was applied.A thin 1μm layer thought to be a hybrid of resin and dentin, was detected using SEM.XMA also exibited the demineralized dentin with a 1μm layer.

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The authors previously reported that the tensile strength and elongation of dental casting Ni-Cr alloys for crown and bridge were greatly affected by the casting method.The Present study was undertaken to find out the causes of the differences in tensile properties among the different casting methods.A close correlation was found between tensile strength and Vickers hardness of the castings of five commercial Ni-Cr alloys only when they were prepared with a casting machine composed of induction melting in Ar gas atmosphere and vacuum-Ar gas pressure.Thus, the tensile properties of the castings made by the other casting methods might have been markedly affected by some casting defects.This was confirmed by the fractographic cbservations of the specimens.On the fracture surfaces of the castings showing lowered tensile properties, dendritic patterns were very often observed together with or without intergranular facet patterns.The dendritic patterns were regarded as those of the inherent gas porosity surfaces for the alloys containing lower Cr, Si and Mn contents and of the hot tear surfaces for the one containing extremely higher C content.

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The image analyze system was applied to determine the efficiency of six amalgamators counting the ratio of amalgam alloy particles in a base material.An equal weight(0.2g)of the alloy and clay were mixed for 2 to 120 seconds, and the digital image of cross-section of the mix was taken by a CCD-TV-camera under a microscope.The image was filtered and processed at three densities before the measurement.Accurate re-producibility of the ratio of mixed part was obtained by this system.The results indicate that several factors affect the mixing efficiency of amalgamator besides the frequency.

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HNPM, Phenyl・P or 4-META is the methacrylate which contains the hydrophobic and hydrophilic groups in its molecule.These monomers have biocompatibilities or affinities for tooth substrates, so they are infiltrated to tooth hard tissues.Since these monomers have co-polymerizied in tooth substrates, high adhesion is achieved.To investigate the pulp response to MMA-TBB resins containing these adhesive monomers, we made a pathological study compared with Clearfil・F on dogs'permanent teeth.The results were as follows.1)Pulp response to MMA-TBB resins containing adhesive monomers was greater than that of Clearfil・F because of the stimulus of MMA at 1 and 4 weeks postoperative period.However, after 8 weeks, pulp response was low and there was little difference from Clearfil・F.2)Pulp response to MMA-TBB resin including HNPM was high during short term postoperative period compared with Phneyl・P or 4-META because of the difference of function of adhesive monomer.After 8 weeks, bacteria layers were found on some of the cavity floors of HNPM.

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Seven Cu substances containing(up to 30%)experimental Ni-Cr alloys were prepared and the castability of the alloys were evaluated by the mesh grid pattern.This method employs reproducible specimen patterns and the castability value of metals and alloy is readily determined.With the increase to Cu content, the solidus and liquidus points of the Ni-Cr alloys shifted downward, and the castability values of the Ni-Cr alloys increased with increasing Cu content.Mechanical properties of Ni-Cr alloys gradually increased with increases in the Cu content in the range from 0 to 20%.

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The effects of Cu content on the corrosion resistance of Ni-Cr alloys were investigated.Cu was added in 5wt% increments to 30wt% in Ni-15Cr alloys.The alloys were evaluated in as-cast condition using Ringer's solution.By applying the square wave current method, the polarization resistance was measured for 50 days, along with corrosion potential.The average corrosion rate was calculated from the weight loss of test pieces.The corrosion potential became noble and polarization resistance increased with addition of Cu.The results indicated that the tendency for Ni-Cr alloys to passivate was enhanced by the addition of Cu.X-ray microanalyses on tested specimens revealed the presence of segregations and Cu rich regions were corrosion resistant.It was also demonstrated by atomic absorption spectrophotometry that Ni was dissolved into Ringer's solution whereas the amounts of Cr and Cu ions were small.The average polarization conductance values during the test period were related to the real corrosion rate as:i_corr =K・Y_corr The constant K value for Ni-Cr alloys determined in Ringer's solution at 37℃ was 26mV.

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We have reported that 4-META/MMA-TBB resin shows high tensile bond strength to enamel and dentin, because the resin easily penetrates the tooth substrates.Tensile bond strength to sintered hydroxylapatite, fluoroapatite, and their mixture with 4-META/MMA-TBB resin was measured in order to assess the relation 4-META and hydroxylaptite.Higher tensile bond strength was obtained for the apatites that have rougher surfaces.The bond strength increased by the pretreatment which leached more Ca²⁺.The best pretreatment solution was 10-3, and the date suggested that ferric ion promotes the curing of the resin on the surface.It was found that 4-META/MMA-TBB resin contains 4-MET derived from 4-META, and 4-MET was taken up by apatites.4-META had good effects on the penetration of resin monomer to the roughened surface of apatite.

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Physical properties of polynorbornene and polynorbornene heated in air and in vacuo were investigated.Polynorbornene had a glass transition temperature of 41.5℃.The polymer began to oxidize in air at a temperature of about 130℃.The quantities of hydroperoxide and calbonyl groups in the polymer increased with oxidation.It was thought that the x-ray diffraction peak at 2θ≈18° corresponds to amorphous halo.This moderately sharp peak suggests that molecules in the polymer are oriented relatively with regularity.It was found that the polynorbornene is a polymer having the double bonds.

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Total expansion of three commercial and five experimental phosphate bonded investment were tested.Total expansion was obtained by calculating setting expansion, hygroscopic expansion and thermal expansion.Followings were the results.1)The setting expansion in the mold of hydrocolloid impression was larger than that in the mold of Teflon with the numerical values being about three times to fourteen times.The investment mixed with the special liquid showed larger setting expansion than that mixed with water.2)The investment set in the mold of hydrocolloid impression and the water added investment generally showed less thermal expansion.One of them showed thermal contraction.3)Hygroscopic expansion was remarkably large in the ratio of each expansion to the total expansion, thus, the total expansion was not same.

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