Compression test and micro Vickers hardness test were done using small cylindrical enamel and dentin specimens separated from human tooth.Influences of the height/diameter ratio of specimens, compression speed and hardness on compressive properties such as proportional limit, yield strength, crushing strength, modulus of elasticity, compression were measured.The height/diameter ratio of specimen had no influence on compressive properties of enamel and dentin.Compression speed influenced some of compressive properties.A good correlation was observed between compressive properties and hardness of enamel.Compressive yield strength of dentin was found to be correlated with Vickers hardness.

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The effect of additives on mechanical properties of composite resin was studied.A paste including matrix resin, filler and additive was cured.Flexural strength, compressive strength and Brinell hardness were measured.The fillers used were alumina and silica glass, etc.and additives were 4-META and methacrylic acid.It was concluded that 4-META, an adhesion promoting monomer, was effective for enhancement of mechanical properties of alumina filled composite resin.Silane treatment had no effect on alumina.The mechanical properties of composite resin were also improved by addition of methacrylic monomer with carboxylic groups.

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The working time of elastomeric impression materials determined according to dental standard specifications are not generally consistent with practical experience.The purpose of the present study was to determine the working time of four modern elastomeric impression materials suitable for single-phase impression technique:1)according the testing procedure described in ADA, Specification No.19, 2)by an oscillating rheometer test and 3)by assessing the die accuracy of impressions made at stepwise delay intervals until, due to the increased consistency of the mix, the production of further impressions was impossible.Another aim of the study was to test the relationship between the results of the accuracy test and the indirect simple standard methods used.The working times found by the three different methods are not generally consistent.The results of the ADA working time test proved useful when compared with the results of the die accuracy test.Depending upon the type of the impression material used and the time of impression taking, a considerable amount of elastic stress may be present.However, these internal stresses are almost totally released while the impression is in situ.Consistent accurate impressions were produced from the four elastomeric materials tested, while the consistencies were still suitable for clinical application.Thus, it is unlikely to overrun the working time.

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In an attempt to have a cavity liner that can adhere to tooth substance with no irritation to the pulp, 4-iodobutyl methacrylate-acrylic acid copolymer liner was prepared.A thin layer(10-20μm)of this hydrophilic cavity liner was applied, with a small brush, on human tooth dentine surface on which the smear layer had been previously removed by 1% EDTA solution.After the application of polycarboxylate cement(PCC)on the lined dentine surface, the adhesive strength between PCC and dentine was evaluated.Without the liner, the average adhesive strength of PCC to dentine was 0.0MPa and 90% of the destruction between dentine and PCC was interface failure.On the other hand, the average adhesive strength of PCC to the lined dentine was 0.6MPa and 90% of the destruction was a mixture of cohesive and interface failure.After the destroyed dentine surface was washed with distilled water, the sample was dried and prepared for scanning electron microscopic examination.In the case of PCC without the liner, the orifices of dentine tubles were exposed, while in that of PCC with the liner, most of the orifices of dentine tubles were sealed by cement.This cavity liner with pendant iodide is considered to react chemically with collagen.In addition, iodine is thought to be gradually released from this liner.

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Higher-order structures of dentin collagen affect the bond strength to dentin with 4-META/MMA-TBB resin.Collagen was denatured by heating of dentin at 60℃, 85℃ and 100℃ for 15 and 30 min, and the bond strength decreased from 18MPa to less than 7.5MPa even when 3% ferric chloride in an aqueous solution of 10% citric acid(10-3)was used.Ferric chloride in 10-3 solution had little influence on collagen denatured by heating.On the other hand, glutaraldehyde modified the collagen by crosslinkage and the bond strength recovered to 18MPa.

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The usefulness of an organ culture method using chick embryo femurs was investigated to evaluate the biocompatibility of biomaterials.Stainless steel wire was inserted into the distal epiphysis of the femur.The tissue reaction around the wire was assessed by histochemical examination.The elements solubled into the tissue around the wire were measured by the X-ray microanalyzer.The femurs did not show growth inhibition.Histologically, however, fibrous connective tissue and a paler cartilage matrix were observed in the tissue adjacent to the wire.In this matrix, the necrotic cells were observed and iron was detected by the X-ray microanalyzer.

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Three experimental light-cured bonding resins containing 6-methacryloyloxyethyl naphthalene-1, 2, 6-tricarboxylate anhydride(MENTA-126), an adhesion promoting monomer, were prepared and evaluated by measurement of the tensile bond strength to tooth substrates.The bond strengths of seven commercial light-cured composite restorative systems were also measured to obtain the comparative data.One of the experimental light-cured bonding resins, containing MENTA-126, HEMA, ethoxylated dimethacrylate of Bis-phenol A, camphorquinone as a photo-sensitizer, and(N, N-dimethylamino)ethyl methacrylate as an accelerator, showed bond strengths of 130〜150kgf/cm² between etched enamel and light-cured composite resin or unfilled resin.The values for dentin treated with 10% citric acid-3% FeCl₃ solution were 40〜60kgf/cm².These bond strength mediated by the light-cured MENTA bonding resin were comparable to the maximum value obtained from the bond strength measurements for seven commercial light-cured composite restorative systems.It was confirmed that MENTA-126 contributed to good adhesion of the experimental light-cured bonding resin to teeth.The importance of hardening ability of bonding resin itself for bonding between light-cured composite resin and tooth substrates was also suggested.

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To confirmed that CaSO₄・2H₂O can grow epitaxially on hydroxyapatite crystals, the crystals were introduced into metastable solutions of calcium sulfate supersaturated with respect to CaSO₄・2H₂O.Upon introduction of the crystals, solution calcium concentration decreased.This finding strongly suggests that CaSO₄・2H₂O precipitates directly on hydroxyapatite crystals, indicating that the crystals are a excellent nucleator for CaSO₄・2H₂O.Transmission electron micrographs of reaction solids confirmed that CaSO₄・2H₂O crystals growed epitaxially on hydroxyapatite crystals.

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The relation between residual stress in injection molded specimens and molding conditions was determined by photoelastic analysis.The higher the temperature of resin or die within our molding conditions, the wider the distance of isochromatic fringes in molded specimens and the gentler the stress gradient in the specimens.However, when the temperature of resin or die was raised, stresses were concentrated in the neighborhood of the gete.One of principal stress trajectories derived from isoclinic patterns coincided roughly with the directions of flow in molten resin, and the other coincided with shapes of flowing resin front.Maximum principal stresses of the 0.55, 0.75, 1.0 and 1.5mm thick specimens were 376.2, 276.0, 207.0 and 138.0kgf/cm², respectively.

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The variations of temperature of simply modified dental-casting-full-crowns at solidification time were simulated by the finite-element-method.The solidifying process of chromium-nickel alloy was different from that of gold-palladium-silver system alloy.The temperature of castings in chromium-nickel alloy was differed with the location.This phenomena was caused by low thermal conductivity of alloy at solidification time.Castings of gold-palladium-silver system alloy had a homogeneous temperature at solidification time.In the case of thin castings of chromium-nickel alloy, the difference of locational temperature were selectively increased.Simulation of solidification-process by the finite-element-method was a suitable technique for dental casting.The results of simulation allowed prediction of the location and form of crack and shrinkage hole in castings.

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To improve the properties of crown and bridge resins, epoxy dimethacrylates(EpDMA)of three different molecular lengths were synthesized, and the properties of experimental crown and bridge resins prepared from them were examined.EpDMA were synthesized by the addition of methacrylic acid to epoxy resins of bisphenol A type.They were expected to be excellent monomers for crown and bridge resins, based on their structural features of alternating rigid bisphenol A units and flexible alkoxide units.Experimental crown and bridge resins were prepared by curing of EpDMA and TEDMA comonomers as liquid components and PMMA as a powder component.The proportion of powder to liquid was one to one by weight.The concentrations of EpDMA and Bis-GMA were 0, 25, 50, 75 and 100mole% against TEDMA comonomer in the liquid components.The properties of the cured resins were investigated as a function of EpDMA or Bis-GMA concentration in a liquid component, and found to change in the following way.As the concentration of EpDMA increased, the hardness, the proportional limit of compression, the modulus of elasticity and the abrasion resistance rose, while the water sorption decreased.The tensile strength, the compressive strength and the transverse strength were maximum in a certain concentration range.

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In order to develop a silane coupling agent that has excellent durability, the influence of the functional group, such as chloro and ethoxy groups of the agent, on the improvement of the silica surface was investigated.The contact angle of water against the silica surface treated with several kinds of γ-methacryloxy-propyl-chlorosilanes did not depend on the number of the chloro groups, and thus the effect of treatment was considered to be the same.However, the tensile strength of the resin against this silica surface differed among them.In addition, adhesional failure occurred in γ-MPMCS-treated silica, while cohesional fracture of resin occurred in γ-MPTCS-treated silica.The adsorption mechanism differed among the silane coupling agent that have several kinds of ethoxy groups(γ-methacryloxy-propyl-ethoxysilane);the amount of the mobile component in the ESR spectrum of the spin-labeled agent mixed with γ-MPTES increased, compared with the spectrum of the agent mixed with γ-MPMES, when these agent were absorbed on the colloidal silica.Thus, there was a good correlation between the adsorption mechanism and the bonding strength of silica/matrix resin treated with silane coupling agent.

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I examined the degree of deformations with respect to the thicknesses of the cast crowns under conditions of various settings and thermal expansions.It was found that a high degree of deformation of the"Arciform"in the inner side and outer side, and a decrease of thicknesses occurred in the cast crowns that were made of the commercially available expansion investments.Almost no"Arciform"deformation in the inner side and outer side occurred, and the symmetries of those values were close to the original dimensions in the cast crowns that were made of non-expansion investments.The investments in which the setting expansion was inhibited were experimentally made.Silght contraction was observed in the inner side, and the outer side values and thicknesses were close to the original dimensions, and in the cast crowns that were made of this experimental investment.These results indicate that setting expansion is a great factor in the deformation of cast crowns.

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