We prepared 3 types of disinfecting-fixing solution for alginate impression materials including;(1)0.5% NaClO-0.5% CaCl₂-1.0% Na₂SO₄, (2)2.0% GA-0.5% CaCl₂-1.0% Na₂SO₄, and(3)1.0% Ca(ClO)₂-1.0% Na₂SO₄. Results showed that for the 4 types of commercial alginate products tested, all three solutions caused smaller weight changes in the impression materials and less surface roughness in the stone cast than 0.5% NaClO and 2.0% GA single solution. Furthermore, a decrease in surface roughness of the stone cast was observed after using CaCl₂ which allowed a gel to form on the surface of the impression. This gel decreased the amount of water absorption.However, Na₂SO₄ caused a decrease in the amount of gel formed by CaCl₂, resulting in a lesser amount of syneresis in the impression. Thus, it can be considered that disinfecting-fixing solutions composed of either CaCl₂, Na₂SO₄ and hypochlorite or CaCl₂, Na₂SO₄ and glutaraldehyde may be useful in stabilizing the dimensional change of impression on immersion, and to decrease surface roughness of stone casts for most alginate impression products.

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In this study, we measured the thermal properties of dental metal alloys used in dental practice, and compared them with those of dental cements and PMMA.Materials used in this study were 20K(CG), 12%-Au-Ag-Pd(CW), Ni-Cr(ST, DN), Co-Cr(SC)and Titanium alloy(KS).Thermal properties were measured by TC-2000L(Sinku Riko)using the xenon flash as a light source.Thermal conductivity of each metal alloys was higher than those of luting cements and denture base resins.Thermal conductivity of metal alloys ranged from CG>CW>KS>SC>ST>DN in order highest to lowest.It was confirmed that Titanium alloy not only had a higher thermal conductivity but was also light weight.

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This study investigated the effects of light source intensity(500, 1, 000 and 1, 500W・m^-2), exposure duration(20, 40 and 60 seconds)and filler type(microfill, quartz and silica glass)on the cure depth of experimental BisGMA-based and UEDMA-based light-activated composite resins.The light source intensity significantly affected the cure depth for all composite resins tested.Increasing the light source intensity and exposure duration significantly increased the cure depth.The results of this study indicated that the difference in refractive indices between resin matrices and siller particles plays a significant role in controlling the light intensity in composite restorations.

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Chitosan is a polysaccharide extracted from crustacea.Chitosan sol is produced by dissolving chitosan in a solution of organic acids.Chitosan film can be fabricated from chitosan sol, which has been neutralized with 5% sodium polyphosphate solution and gelatinized.Chitosan film is an elastic solid similar to rubber.Chitosan film should have a certain level of strength, but can be cut with a knife or scissors prior to placing the chitosan film in vivo.Since the chitosan film will be absorbed in vivo and replaced with bone structure, the level of strength required is not high.In the present study, the various relationships between the amount of hydroxyapatite added and the pH values, viscosity, shrinkage, hardness, tensile strength and elongation of the chitosan film were examined.The main results were as follows;By increasing the amount of hydroxyapatite, pH value and viscosity increased, while the shrinkage decreased.The chitosan film with 4.0g of added hydroxyapatite(HA/chitosan=4/11)exhibited the greatest degree of hardness and tensile strength.However, elongation of the chitosan film decreased as the amount of added hydroxyapatite, increased.

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This study evaluated the application of amorphous-coatings by sputtering method in order to improve corrosion resistance in super-elastic Ti-Ni alloy used for orthodontic appliance.It is recognized that Ti-Ni alloys possess inferior corrosion resistance when formed in slender shapes with sharp edges, such as orthodontic wires.Since amorphous alloys have uniform structures and no grain boundary, they are expected to show excellent corrosion resistance.Ti-Ni wires were coated with 56.0Ta-32.4Fe-8.4Cr-3.2Ni(at%)amorphous film by the sputtering method.Corrosion resistance was evaluated by electrochemical methods, and super-elastic characteristics was measured by three point bend tenting.Results lead to the conclusion that amorphous coatings are useful for improving corrosion resistance in Ti-Ni orthodontic wire, though the bending characteristics of wires was slightly changed during the coating process.

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The stability of thiobarbituric acid monomer adsorbed on a dental alloy was examined after immersion in water at 60℃ for 1 day to evaluate the durability of the adhesion interface between resin and the alloy primed with the acid.Thiobarbituric acid monomer, 5-allyl-2-thiobarbituric acid or 5-(4-vinylbenzyl)-2-thiobarbituric acid(5VS)was dissolved in either MMA or ethanol.Thus, four kinds of solutions were employed for surface treatment.The application of the treatment agent to alloy surfaces resulted in molecular adsorption of the acid.The contact angle of water on the metal surface was measured and tensile bond strengths of resin to the metal adherend were determined after 2, 000 thermal cyclings in water at temperatures of 4 and 60℃.Measurements taken before and after immersion in hot water were compared as estimates of the durability of resin adhesion to the acid-treated metal.The tensile bond sterngths of resin to alloy subjected to hot water immersion decreased significantly, when adsorbates were weakly bound to the adherend surface.However, use of 5VS ethanol solution as a surface treatment agent yielded relatively higher bond strengths of resin to precious metal alloys even after the hot water treatment.The results indicated that the bond between resin and precious metal alloy primed with 5VS possessed longer-term durability against water.

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Single-edge notched specimens of six commercial composites for indirect and direct posterior use were prepared by both initial light curing and post-cure heat treatments at 100〜120℃ for 10-15 minutes after initial light curing. Specimens were tested for fracture toughness(K_IC)in a 3 point bending test after:a)1 day aging in air at 23℃, b)1 month immersion in water at 37℃ and c)1 month of thermal-cycling between 4℃ and 60℃, (approximately 10⁴ cycles). The K_IC increased for most materials without post-cure heat treatments after either water immersion or thermal cycling because of the post-curing effect. However, the K_IC in some materials was significantly lower after thermal cycling than that after water immersion, which suggested that thermal cycling might accelerate the deterioration of composites.However, the effect of thermal cycling on the K_IC of materials that had undergone post-cure heat treatments differed by the type of material. The K_IC of some materials after thermal cycling was significantly higher than that after water immersion, which suggested that the internal stress produced by post-cure heat treatments contributed to increases in K_IC for some materials, resulting in less relaxation of that stress by thermal cycling.

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To prepare decayed teeth for restoration, dentists use air-turbine handpieces to cut through the decayed areas.In this study, to evaluate torque and work efficiency in air-turbine handpieces, bladeless burs driven by two air-bearing and two ball-bearing handpieces were pressed against hard ceramic, while rotational speeds of the bur and applied loads were simultaneously measured.The analysis confirmed that ball-bearing handpieces had higher torque properties than air-bearing handpieces.For all workpieces, the relationship between applied load and work efficiency followed convex parabolic curves.To effectively utilize miniature-type and standard-type air-bearing handpieces and standard-type ball-bearing handpiece, it was speculated that the vertical applied load should be set below 100gf.To effectively employ a high-torque-type ball-bearing handpiece, it was suggested that the vertical applied load should be less than about 400gf.

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According to the classification system proposed by HOSODA et al., eleven resin composites consisting of four anterior, two posterior, four universal and one experimental resin were categorized into three types based on the elemental compositions and size distributions of the filler particles which were analyzed by an energy dispersive X-ray microanalyzer(EDX)and observed under SEM.Helio Progress and Multifil VS were classified as MFR(Microfiller Filled Resin)type resins.PALFIQUE ESTELITE was classified as SFR(Submicrofiller Filled Resin)resin.The other eight resin composites were classified as Semihybrid resins.Some modifications were introduced into the proposed classification system through this study.SFR resin which consists of spherical submicrofillers was newly classified into that category.

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Dentin primers containing N-(Hydroxyethyl)methacrylamide(EMA)and N-(2, 3-Dihydroxypropyl)methacrylamide(DMA)were prepared to improve the bond strength of light-cured composite resin to dentin treated with a 10-3 solution.All dentin primers, except for those containing 10wt% and 60wt% EMA or 10wt% DMA, showed improved bond strength.The dentin primer containing 40wt% EMA demonstrated a higher bond strength than that containing 35wt% HEMA.Dentin primer containing 50wt% DMA showed a higher bond strength than that containing 45wt% GM.Acid-proof dentin layers were about 1μm at the interface between all resins and dentin as observed by SEM.SEM revealed that specimens after shear bond tests had an acid-proof dentin layer cohesion fracture, resin cohesion fracture and cohesion fracture.

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