To improve the adhesion between composite resin and tooth, a new primer containing glutaraldehyde, HEMA and MTYA (O-methacryloyl tyrosine amide) was prepared. First various primers are prepared by changing the combination of glutaraldehyde, HEMA and MTYA. Clearfil New Bond^® and Clearfil FII^® were used. The tensile bond strengths after storage in 37℃ water were measured. 1-35 (MTYA) was most effective for improving the adhesion to dentin. 1-35 (MTYA) consists of 1% glutaraldehyde, 35% HEMA, and 3% MTYA.With 1-35 (MTYA) treatment, the bond strengths to dentin were 10 MPa with 10% citric acid etching, 16 MPa with 40% phosphoric acid etching, and 11 MPa with 10-3 etching.Scanning electron microscopy revealed that the thickness of decalcified dentin was the same as that of resin reinforced dentin. As for adhesion to enamel, the bond strengths were 25 MPa with 40% phosphoric acid etching.The primer 1-35 (MTYA) was found to be very effective for improving the adhesion between composite resin and tooth.

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The study was conducted to evaluate the effect of accelerators on the compatibility of dental stones with agar impression material. A dental stone without any additives (pure alpha calcium sulfate hemihydrate) was mixed with the aqueous solution of potassium sulfate, Rochelle salt and sodium chloride at different concentrations, and the slurry was poured on 10% agar gel. After setting, the surface roughness of the set stone in contact with the agar was measured. The surfaces were also examined using an X-ray diffractometer and a scanning electron microscope. In addition, the setting time of these stones was measured. The surface roughness of the set stone on the agar decreased as the concentration of the accelerators increased. A significant positive correlation was found between the surface roughness and the setting time. The diffraction X-ray intensity of the calcium sulfate hemihydrate on the stone surface decreased as the concentration of the accelerators increased. A significant positive correlation was found between the intensity and the surface roughness. The diffraction X-ray intensity of the calcium sulfate dehydrate on the stone surface increased with the concentration of the accelerators. A significant negative correlation was hoted between the logarithm of the intensity and the surface roughness. The surfaces of the set stones with the accelerators mostly consisted of very fine and needle-like crystals.

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The present studies are concerned with the development of visible light-cured composite resin. The author, using the synthesized cyclophosphazene monomer, 4PN-(TF)₁-(EMA)₇, as monomer, with monomer and filler added, examined the physical properties. The optimum monomer composition for visible light-cured composite resin was found to be: 80% of 4PN-(TF)₁-(EMA)₇ monomer with 20% of 2.6E as a comonomer, to which 0.28% of camphor quinone, 0.12% of benzil and 1.56% of ethyl p-dimethylamino benzoate are added as photosensitizers. The visible light-cured composite resin prepared by mixing filler with the above-shown monomer composition exhibited increased transverse strength and compressive strength with the increase of the mixed amount of filler, while water sorption, solubility, thermal expansion coefficient and polymerization shrinkage decreased. The test product of visible light-cured composite resin showing optimum physical properties was, as follows: the above-shown monomer composition with 80% of filler mixed. The product's transverse strength and compressive strength were respectively 90 and 303 MPa, and its hardness was, 90.5 H_RS. On the other hand, the thermal expansion coefficient and polymerization shrinkage were low (15.4×10^-6/℃ and 1.30vol%, respectively).

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A wax-pattern like a crown must expand in the outer direction by expansion of investment during setting. Accordingly, to suppress the expansion of investment during setting, some load, which was estimated at the resistance of wax pattern against expansion of investment, was applied and the setting and hygroscopic expansion was measured. From this experiment, setting expansion of gypsum bonded investment decreased in proportion to the applied load. Hygroscopic expansion was influenced to a greater extent by the rate of increase of the applied load than that of setting expansion. On basis of a time-expansion curve, we described the time-expansion gradient (de/dt) curve and examined the effect of the applied load on maximum expansion gradient. It was found that the maximum gradient in hygroscopic expansion was significantly affected by the applied load.

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Four Ni-Cr binary alloys (5%Cr, 10%Cr, 15%Cr, and 20%Cr in weight) were oxidized at 1, 000℃ in air and the oxidation process was investigated by thermogravimetric measurement (TG), electron probe microanalysis (EPMA), and X-ray diffraction. For 5%Cr and 10%Cr alloys, ‘breakaway’ and multilayered structures occurred in spite of the constant temperature and ‘pegs’ of CrO₃ developed at the innermost oxide layer. For 15%Cr and 20%Cr alloys, the inner oxide layer consisted of almost pure Cr₂O₃ but peg formation was not observed. In the case of oxidation of pure Ni covered with thin vacuum-deposited Cr film, thin Cr₂O₃ layer (marker) existed at the intermediate position in the NiO scale, suggesting oxygen gas diffusion. In conclusion, the oxide scale feature (multilayered structure and peg formation) is due to the behavior of oxygen, such as inward diffusion.

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The reproducibility of denturous working models obtained from various impression materials was measured using a three-dimensional measuring system. In additon, the influences of various impression materials were evaluated by the normal deviation from profile measurement. In the working model obtained from alginate impression, deformation occurred in the anterior of the maxilla and mandible and also in the posterior of the mandible. In the working model obtained from condensation-type silicone rubber impression, the maxilla showed the highest reproducibility among all models, and the mandible deformed largely on the position of molars. In the working model obtained from addition-type silicone rubber impression, both the maxilla and mandible showed the largest deformation. It was possible to evaluate the reproducibility of a denturous working model effectively by the normal deviation obtained from the profile measurement.

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A system which includes a silane coupling agent for activating the surface of SiO₂ surface, for repairing fractured porcelain was developed. The inorganic filler in composite resin was mainly composed of SiO₂. In this study, we investigated whether the treatment of composite resin with a silane coupler has any effect on the shear bond strength of repaired composite resin. The bond strength between the extracted human enamel treated with the silane coupler and prepared composite was also mearsured. The bond strength of repairing resin to the composite treated with silane coupler was greater than that to the untreated composite, and the same results were obtained with the treated human enamel. These results suggest that the treatment of the composite or human enamel with a silane coupler can effectively increase the bond strength.

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Studies were undertaken to apply a CAD/CAM system to dentistry. The system was designed to make prosthetic appliances automatically in place of routine casting and moulding techniques. Three-dimensional (3D) measurement of coronal figures is necessary for CAD and CAM. We examined 2 types of 3D measuring methods. One was the slice cutting method in which sectional data were obtained from 4 times large plaster model. The other was the laser beam measuring method in which the 3D position is calculated from the change of reflected beam on CCD. The first method required much time to measure and much effort to rearrange the data. The second method time-saving automatic measuring method, which appears suitable for our dental CAD/CAM system.

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The adaptation of an experimental composite resin system to dentin cavity wall mediated by three experimental bonding agents containing a functional monomer, 4-META, was evaluated by measuring the wall-to-wall contraction gap and SEM observation using the replica technique. Among the tested materials, the combination of the dentin cleanser of 0.5M EDTA, dentin primer of 35% HEMA, an experimental bonding agent composed of 4-META, aromatic dimethacrylate and PMMA and the UDMA based light activated composite resin containing 66% organic microfiller exhibited complete bonding between the resin and the dentin cavity wall.

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In this study, the physical and mechanical properties of three kinds of posterior composite resins (Bellfirm P, Clearfil Posterior and Micro Jar) were examined for 3 years afterward and compared with one conventional anterior composite resin (Clearfil FII), mainly according to ADA Specification No.27 and ISO 4049. In the examination of water sorption, four composite resins tended to show various increases in water uptake during the 3-year period. One posterior composite resin (microparticle filled resin) was more absorbable and soluble in water than the other posterior and anterior composite resins with conventional fillers. In SEM observations, many air bubbles were found inside the specimens of all four composite resins, because of all mixing type composite resins. The surface layer of all four composite resins showed signs of disintegration, but the center layer of specimens were not disintegrated. As for tensile and transverse strength, all four composite resins reached an equilibrium after 3 days and the values remained steady for 3 months. After about 6 months or 1 year, however, they tended to decrease continuously. In the mechanical properties after 3 years, three posterior composite resins were the same or inferior to the anterior composite resin in tensile strength, but the former was superior to the latter in transverse strength.

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Poly (ethyl methacrylates) of different molecular weights were synthesized by suspension polymerization. These polymer powders, and a liquid that contained butyl phthalyl butyl glycolate and ethyl alcohol were used. The storage modulus G′, dynamic viscosity η′ and loss tangent tanδ of a mixture of powder and liquid were determined over the frequency range of 0.05 to 70 Hz at different temperatures. By the application of the time-temperature superposition principle, the curves of G′, η′ and tanδ versus frequencies at different temperatures for each material were superimposed to a single master curve. The remarkable effects of molecular weight of polymer on the viscoelastic properties of the materials found at the low frequency region; the lower the molecular weight, the lower the storage modulus G′ and the higher the loss tangent tanδ. These results suggest that in the use of poly (ethyl methacrylate) as the powder of tissue conditioner, the polymer should be adjusted to a lower molecular weight so that the material flows and deforms according to the recovery of the deformation of tissue.

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Au-Cu binary alloys with various gold contents were investigated with regard to dissolution of gold and copper under dynamic extraction of 200 rpm at 37℃. Measuremens of the extracts were carried out at two-week intervals during a 20-week period. Dissolution of copper at the first extraction was found to be the largest amount among all extractions, followed by a gradual decrease with further extractions. Dissolution of gold, on the other hand, appeared to be small at each extraction compared with copper. Dissolution of copper was markedly decreased when gold contents exceeded 66.7 wt% within the alloy. The present results may shed light on understanding metal corrosion and biocompatibility of multi-component gold alloys.

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To make a smooth final glossy surface of dental ceramics, ultrasonic lapping of Livdent^®, Vita VMK^®, Dicor^® and Macor^® was carried with an ultrasonic polisher (28.5 KHz, 10 W) using the lapping paste of Al₂O₃, CeO₂, ZrO₂-SiO₂, Cr₂O₃ and diamond, and the polishing efficiency and surface texture were examined. Porcelain was polished efficiently only with diamond paste and showed an excellent glazed surface. Macor^® and Dicor^® had better polishibility than porcelain and showed an excellent surface when polished with Al₂O₃, CeO₂ and diamond.

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Plates of tetracalcium phosphate (4CP) cement and α-tricalcium phosphate (α-TCP) cement were immersed in Dulbecco's phosphate buffered saline (PBS) for 6 days. These plates were allowed to examin. Their changes in the structures of these plates were examined by X-ray diffraction, scanning electronmicroscopy (SEM) and quantitative analysis of Ca and P concentrations. Immediately after hardening, the X-ray diffraction patterns of the surfaces of 4CP and α-TCP cement plates show broad peaks compared with the synthetic 4CP and α-TCP powders. This finding suggested that amorphous calcium phosphate had formed on these cement plates. After immersion in PBS, hydroxyapatite (HAp) was produced on the surfaces of 4CP and α-TCP cement plates. Dicalcium phosphate dihydrate (DCPD) was formed on the surface of α-TCP cement plate but not of 4CP. The SEM revealed that the surface of DCPD had converted to HAp after immersion for 6 days. These findings suggest that the surface of the 4CP cement plate more rapidly converts to HAp than α-TCP cement. Powdered X-ray diffraction and the Ca and P mesurements revealed that this conversion was restricted to only the surface layer of 4CP and α-TCP cement plates. However, changes of Ca and P concentrations in PBS immersed cement plates showed that the conversion to HAp was still occurring even after 6 days.

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Photocurable bonding liners for dentin were studied. The liners contained d, l-camphor quinone (CQ) as a photosensitizer, N-phenylglycine (NPG) as a reducing agent instead of N, N-dimethyul aminoethyl methacrylate (DMAEMA), and 4-methacryloxyethyl trimellitate (4-MET), 2-hydoroxy-3-phenoxypropyl methacrylate (HPPM) or 2-methacryroxyethyl p-methoxyphenyl phosphoric acid (CH₃O〜OH) as an adhesion promoting monomer. Bovine dentin was pretreated with 0.5 M EDTA・2Na solution (EDTA5-0) or 0.3 M EDTA・2Na-0.2M EDTA・Fe・Na solution (EDTA3-2) for 60 sec. The tensile bond strength of CQ・NPG・4-MET liner to bovine dentin with EDTA3-2 was 8.4 MPa and that of CQ・NPG・CH₃O〜OH liner was 8.6 MPa. However, CQ・NPG・HPPM liner did not improve adhesion. The findings indicate that NPG acts as a reducing agent in photocuring system and that the combination of CQ, NPG and an acidic monomer (like 4-MET, CH₃O〜OH) achieved good polymerization of the liner.

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Resin cements consisting of TMPT-filler as a powder and a mixture of HPPM and DEGDMA or TEGDMA as a liquid were prepared. Mechanical properties of the resin cements and their tensile bond strength to bovine tooth were investigated in regard to the monomer compositions. The powder-liquid ratio (P/L) was 1:1 by weight. The best results were obtained with HPPM-TEGDMA (4:6, by weight). The mechanical properties of this cement were measured: the compressive strength was 2, 000 kgf/cm², diametral tensile strength 360 kgf/cm², setting time 5 min and consistency 32 mm. The amount of eluted monomers was minimized. The tensile bond strength to enamel etched with 65 wt% phosphoric acid aqueous solution was 42 kgf/cm². However the film thickness was 51.7 μm and tensile bond strength to etched dentin was low.

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To clarify the adhesion mechanism of MMA resin containing 4-methacryloxyethyl trimellitic acid (4-MET) to dental enamel, two kinds of experiments were carried out: (1) Using human premolars, scanning electron microscopic observation and an artificial caries producing test were performed on the enamel surfaces where applied resins had been extracted in hot acetone. At the enamel surface where 4-MET/MMA-TBB or 4-MET/MMA-BPO・Amine resin was extracted, an acid and acetone resistant layer appeared, and prevented artificial caries formation for 7 days. At the enamel surface of 2-hydroxy-3-β-naphthoxypropyl methacrylate (HNPM)/MMA-TBB or methacryllic acid (MA)/MMA-TBB resin, caries-like lesions were 30% smaller than controls, but no acid and acetone resistant layer was detected. (2) On the infrared absorption spectra of the mixture of resins and hydroxyapatite, an absorption band of carboxylate at 1, 560 cm^-1 was found with 4-MET or MA.This suggested reactivity between 4-MET or MA and Ca⁺⁺. The acid and acetone resistant layer on the enamel surface where 4-MET/MMA-TBB or 4-MET/MMA-BPO・Amine resin was applied was produced by the excellent permeability and reactivity of the resins. These properties may contribute toward the high adhesiveness to dental enamel.

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This study evaluated the tensile bond strength of adhesive cements to base and core materials. The bond strength of the butt joint adhesive method was measured to compare with the rein-to-adherent adhesive method, and the influence of surface treatment of cast body on the bond strength was examined. Nine base and core materials as adherents and three adhesive cements as adhesives were used in the resin-to-adherent adhesive method and three adhesive cements as adhesives were used with the butt joint adhesive method, three adherents, two cast alloys and two adhesive resin cements were used. Two adhesive resin cements showed much higher tensile bond strengths to resin core materials. 4META-type resin cement generally yielded greater bond strength than that of BisGMA-type resin cement. The butt joint adhesive method should be adopted as the main test for tensile bond strength of adhesive cements due to its close simulation of clinical conditions and the resin-to-adhesive method might be used as a reference test. The socalled “as-cast” surface might be suitable as an adherent surface of cast specimens for such kinds of tensile bond test.

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