An investigation was made to clarify the factors which have influences upon crushing strength and compressive yield strength of composite resins.Although there are many reports on mechanical properties of composite resins measured by compressive tests, the information provided in these reports can be difficult to interpret and estimate on account of variation in testing procedures.In this study Coremax and Superlux were chosen, which were thought to be example of a conventional composite resin and a microfilled composite resin, to evaluate the significance of factors by variation analysis using the orthogonal table L₁₆. Five factors and their levels selected were as follows:1.Diameter of sample(5mm and 6mm)2.Ratio of length to diameter of sample(2 and 1)3.Individual factor while preparing sample(M and N)4.Lubricant(with and without)5.Loading speed(0.1, 1, 5 and 10mm/min)The samples were prepared according to manufacturer's instructions and packed into P.T.F.E.moulds of appropriate dimensions determined by factor 1 and factor 2.Above procedures were operated by M and N.Three kinds of preservation atmosphere of samples were taken as follows:The lst one was just preserved in air at 23℃ for 15 minutes.The 2nd one was at first stored in an atmosphere of 100% relative humidity at 37℃ for 15 minutes then stored in distilled water at 37℃ for 35 minutes and immersed in distilled water at 23℃ for 10 minutes before testing.The 3rd one was same as the 2nd one at first then stored in distilled water at 37℃ for 24 hours and shifted to distilled water at 23℃ for 10 minutes before testing.These age of specimens were shortened as 15M, 1H, and 24H.Each samples were subjected to axial loading at a rate of 0.1mm/min, 1mm/min, 5mm/min, and 10mm/min in a testing instrument(Instron Universal Testing Instrument, model 1125, Instron Corp., USA).Silicone grease was used as an lubricant.Crushing strength and comperssive yield strength of each materials of each age were calculated on the load-compression curve.The results obtained in this study were summarized as follows:1.Crushing strength was influenced by all five factors adopted, but compressive yield strength was affected significantly only by loading speed and wasn't influenced by other factors very much.2.Crushing strength at age 15M was rather high but compressive yield strength at age 15M is low.The ratio of compressive yield strength and crushing strength became stable after age 1H.The stress relaxation curves at different loading speed were measured using three composite resins.And it was considered that stress relaxation of samples during the compressive testing had effects on the properties of compressive yield strength.Eight commercially available composite resins and PMMA employed as control were evaluated on the basis of compressive yield strength.Three samples(5.0mm in diameter, 5.0mm in length)of each materials were prepared and stored in distilled water at 37℃ for 24 hours and then tested at a loading rate of 1.0mm/min.It may be concluded that strength of materials were evaluated more reasonably by compressive yield strength than by crushing strength.And it was clarified that compressive yield strength of newly developed composite posterior restorative resins were very high but those of microfilled composite resin were rather low.

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4-META adhesive resin cement was developed.4-META has good affinity with hard tissues due to the hydrophobic and hydrophilic groups.The physical properties were measured:setting time 7 min.16 sec., film thickness 16.5μ, compressive strength 1720kgf/cm², tensile strength 205kgf/cm², and disintegrated ratio 0.01%.The tensile adhesive strength to pretreated enamel was 90kgf/cm², pretreated dentin 50〜55kgf/cm², several dental alloys sandblasted with aluminium oxide including gold and Ni-Cr etc.75〜100kgf/cm², Longer tags in etched enamel and resin reinforced dentin in pretreated dentin which were formed by the application of 4-META were observed by SEM.Resin reinforced dentin is a mixture of cured monomers and dentin at molecluar level, and has good resistance against acids.

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To study the characteristics of resin-bonded apatites as a substitute for conventional composite resins, hydroapatite was synthesized at 80℃ and pH7.4, and mixed as filler with 2.2'-Bis(4-methacryloxydiethoxyphenyl)-propane.BPO and DHPT were used as polymerization initiators.The inorganic and organic phases of products were identified by X-ray diffraction and IR spectroscopy.The compressive strength and Knoop hardness of the composites increased with the increase of apatite content, but were less than those of enamel and conventional composites.The thermal expansion coefficient of the composite with apatite-resin ratio Ap/R=1 was almost equal to that of tooth.In tooth cavities, the composites seemed to adhere well to enamel without a bonding agent.

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The present author examined composite resins, glass ionomer cements, and silicate cements to ascertain the properties and causes of color shift, which might be ascribed to the combination of metallic elements and hydrogen sulfide gas.The materials employed were:9 composite resins, 3 glass ionomer cements and 1 silicate cement, all commercially available in the market.After exposing the above materials to the hydrogen sulfide gas, the color shift of each restorative material was analyzed with a dental color analyzer(Dental Color Analyzer NS-100, J.Morita Corporation)and was also visually observed.The following results were obtained:1)Most of the specimens exposed to the hydrogen sulfide gas showed large discoloration:especially, Isopast, Ionomer Type II, Ionomer Type II F, New Lusilex, and Ionodent marked distinguished color shift.2)All of the specimens exposed to the air generally showed smaller discoloration than those exposed to the hydrogen sulfide gas.Little discoloration was observed in Silar, Ionomer Type II, Ionomer Type II F, and Ionodent.3)The visual observation indicated that distinguished color change was ascertained in Isopast, Ionomer Type II, Ionomer Type II F, and Ionodent.On the contrary, New Lusilex, where the dental color analyzer indicated large color shift, did not show any apparent discoloration.

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The distortions of simple inlay type casts under various casting conditions were investigated by measuring the linear dimensional changes in diameter and height, the volume changes and contours of the casts.In the case of a cristobalite and a quartz investment, the casts were markedly distorted, because the rates of the linear dimensional changes in diameter of the casts differed greatly from that in height, and the volume changes did not also agree with the values estimated from the linear dimensional changes in height.The distortions of the casts reached the maximum value in the case of asbestos linning casting method.On the other hand, the concavity was measured on the surface of the all casts.It made the distortions larger.In the case of a phosphate-bonded investment(Ceravest), the distortions of the casts were smaller than in the case of other investments used.It could be seen that a gypsum-bonded cristobalite investment had the effect on restraint of casting shrinkage as well as a phosphate-bonding investment.

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In order to explore the physical properties of ten kinds of the addition-type silicone impression materials on the market, the ingredients of all materials were investigated in this report.Findings are follows.1)It was found that the base paste prepolymers were hydrogen-polysiloxane and the catalyst paste prepolymers were vinyl-polysiloxane.2)Molecular weights of each prepolymer without those of PRECICON increased with increasing the viscosity value of each type(fine, regular, heavy or putty).3)The ingredients of fillers, a contents of which increased with increasing the viscocity value of each type, were SiO₂, quartz, and quartz and Ca compound.4)The shape of the great parts of fillers were similar but those of 3MP were indeterminate, and the distributions of filler size were independent on the viscocity value of materials without PRECICONE.

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The back pressure within the mold cavity during centrifugal casting of mercury was measured using a pressure miniature semiconductor directly inserted into the cavity.The obtained results were as follows:(1)The measured values of the back pressure almost agreed with the calculated values of the pressure at the sprue end that were obtained by applying pressure equation.(2)When sprues were more than 1.5mm in diameter, gas was intermittently exhausted through the sprue and the back pressure increased fluctuatingly.(3)Direct-type air vent as thin as 0.5mm in diameter effectively decreased back pressure and casting time.(4)Effect of attachment of the blind-type air vent on the back pressure was negligible.However, when the area of the vent was enlarged to more than 17% of the surface area of mold cavity, casting time decreased to some extent.(5)Thinning the bottom of investment in casting ring from 12 to 6mm had no effect upon both the back pressure and casting time.

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Alginate impression materials as elastic impression materials, having preferable manipulability and comparatively preferable elasticity, are clinically prevalent.There are 2 kinds of them:powder type and paste type.The powder type is more widely used, for comparatively homogeneous mixing compound is obtainable and it easily be measured.On the other hand, the paste type, as it is used with dental plaster mixed, is hard to form homogeneous mixing compound, and the dental plaster powder remaining in alginate gel, preferable physical properties can hardly be obtained.The author, in order to improve the defect of the paste type, tries to prepare paste-paste type alginate impression material by making the dental plaster powder pasted.That is, to make the plaster powder pasted, the author selects sorbitan trioreate(ST), polyoxyethylene sorbitan trioreate(PST)and propylene glycol(PG)as paste agents, prepares experimental alginate impression materials changing the mixing ratio of paste agent and dental plaster and that of base material and hardener and examines their physical properties.

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Adhesive strength of 4-META/MMA-TTB resin to fresh bovine dentin cleaned by a 10% citric acid-3% ferric chloride solution for 30 sec was 18MPa, on the other hand it decreased to 6MPa when the adhesion was carried out to the dentin etched with a 65% phosphoric acid solution for 30 sec.The strength to the phosphoric acid etched dentin which had been soaked in a 25% glutaraldehyde solution for 10 min increased to 11MPa.But it became lower to 6MPa when the aldehyde soaked dentin was cleaned by a 10% citric acid-3% ferric chloride solution.These results strongly suggest that structure of the collagen plays important role in the adhesion to dentin.The collagen crosslinked by glutaraldehyde has better resistance against the sturctural change during the acid etching.The 10% citric acid-3% ferric chloride solution is not strong enough to remove the smear layer and ingredients in the tubules which had been crosslinked by the aldehyde.The SEM observations suggested that the former 6MPa was due to the interlocking at the tubules but the latter 6MPa was due to the infiltration of monomers into peritubular dentin and intertubular dentin and not to the mechanical interlocking as previously reported.

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The adaptabilities of heat-curing base resins cured by microwave heating and cured in a water bath were investigated.The discrepancies between of the base resins cured in water bath and plaster models were greater than that of base resins cured by microwave heating.The adaptability at the ridge portions of denture base was superior to that at the plaster regions.As a whole, the base resins cured by microwave heating showed better adaptability than that cured in water bath.The temperature of the center of FRP flask rised rapidly above the temperature of the edge of the flask by microwave irradiation.The temperature of the resins began to increase rapidly after microwave was irradiated for 1.5 minutes.On the other hand, in water bath the temperature of the plaster in the flask increase to about 65℃ in 20 minutes, and that of resins began to increase rapidly after placing the flask in water 65℃ for 30 minutes.

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Mono-axial thermal stress σ(t)developed in the rectangular beam of inlay wax fixed at both longitudinal ends during the process of cooling was experimentally determined and numerically analysed according to the following equation:[numerical formula]where α, E, a_T, and T were the coefficient of thermal expansion, relaxation modulus, reducing factor, and temperature, respectively.This equation was derived from the linear viscoelastic theory expanded to non-isothermal system based upon the concept of thermorheological simplicity.Good agreement was obtained between the calculated and found values within the practical limit of variation to estimate shrinkage of wax pattern, which took place when the residual thermal stress was released.The residual thermal stress was less than that predicted from the theory of elasticity, that was, the stress relaxation of inlay wax greatly contributed to reduce the internal stress.To minimize the residual thermal stress they should maintain most suitable conditions during the process of formation, which were concerned with thermal hysteresis, storage temperature, and storage periods.These conditions should be controlled according to the relaxation modulus and reducing factor of the wax used.

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The stress relaxation behaviours of 3types of denture base resins(polymethyl methacrylate, polysulfone and polycarbonate)were examined in water.The relaxation modulus[Er(10)]of heat-cured acrylic resin tested at the temperature of 23℃ was slightly higher than those of other 2 types of resins and was 1.71×10¹⁰dyne/cm².However at the temperature of 37℃ in made little difference in the relaxation modulus[Er(10)]among three materials mentioned above, the relaxation modulus of cold-cured acrylic resin was the smallest in all materials used.Furthermore, in the case of acrylic resins, the decay of relaxation modulus according to increase of temperature was larger than those of polysulfone and polycarbonate resins.From these results, it can be seen that the stress relaxation of acrylic resins occurs more readily than in the case of polysulfone and polycarbonate resins.

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An amalgam alloy, namely Lumi Alloy was investigated by X-ray microprobe and X-ray diffraction analysis.It was found that there were two different compositions.One was roughly composed of Ag 47wt%, Sn 33wt% and Cu 21wt%.The other was roughly Ag 59wt%, Sn 30wt% and Cu 11wt%.The alloy seemed to consist of γ(Ag₃Sn)and Cu₃Sn.Quick reaction of this alloy with mercury was observed.Amalgam made from this alloy exhibited a matrix of γ₁(Ag₂Hg₃)with small reaction phase areas of Cu₆Sn₅.The γ₂(Sn_7-8Hg)was detected in amalgam an initial period of time.But this phase seemed to disappear as time elapsed.The surface structural changes were not marked after immersion in synthetic saliva.

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In order to study the effect of casting methods on exclusion of the air in the mold cavity, K metal and Ni-Cr alloy were cast into the mold made of fused silica without air-permeability.The castability of the centrifugal casting were higher than that of the air pressure casting, regardless of the shape of cavity(inlay or crown type), the diameter of the sprue(1mm or 2mm)and the alloy(K metal or Ni-Cr alloy).This result means that the air in the mold can be easily excluded through the sprue in the centrifugal casting.

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The mechanical and physical properties of the experimental adhesive composite resin were investigated.The curing time of the composite resin was highly dependent on temperature, and its curing behavior was most suitable for cements at the ambient temperature of 37℃.The film thickness of the composite resin was found to be 17μm, which was comparable to conventional cements.The mechanical properties such as compressive strength, transverse strength, diametral tensile strength and Brinell hardness was ascertained to compete with conventional restrative composite resins, and their durabilities in water was extremely superior to ordinary cements.The experimental composite resin turned out to possess excellent adhesive properties to tooth substrates or dental alloys.

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The effect of 3% ferric chloride-10% citric acid or 3% cupric chloride-10% citric acid aqueous solutions which have been found to be effective as pre-treatment solutions for the adhesion between resins and teeth on the radical polymerization of methyl methacrylate(MMA)was investigated.Solution polymerization in p-dioxane and bulk polymerization, keeping the pre-treatment solutions dispersed mechanically, were carried out and the rates of polymerization and the molecular weight distributions were determined.In the bulk polymerization, the rate of polymerization was diminished by the addition of the pre-treatment solutions, and, however, the weight-average molecular weight of polymer went up to about 5×10⁵ in the final curing stage.These results suggest that the effect of the pre-treatment solutions on the polymerization was gradually lowered as the reaction proceeded, although the polymerization was deeply affected by the pre-treatment solutions in the early stage.

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