The purpose of this study was to develop experimental paste-paste-type phosphate-bonded investments and evaluate their clinical use. Powders for Paste 1 comprised a 100-g mixture of cristobalite (95, 90, 85 and 80g) and ammonium dihydrogen phosphate (5, 10, 15 and 20g). These were mixed with colloidal silica liquid, diluted twice with water, and four kinds (A-D) of paste were prepared. Paste 2 comprised magnesium oxide and vaseline. A commercial investment was also tested as a control. Fundamental properties and the casting accuracy with surface roughness were examined. With an increase in ammonium dihydrogen phosphate, extension of the setting time, an increase in setting expansion, and a decrease of thermal expansion were noted. However, the compressive strength after firing was almost the same among experimental investments. The casting from C showed a small gap and suitable surface, and the values were close to those obtained from the control. These results suggest that experimental paste type-investments are applicable for clinical use, and C was particularly promising.

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The purpose of this study was to test the effect of the powder-liquid ratio on the mechanical properties of glass ionomer cements for luting. Two conventional and three resin-modified glass ionomer cements for luting were tested. Each glass ionomer was mixed at three different ratios: (1) the manufacturer's recommended ratio; (2) 30% of the powder was subtracted from the recommended amount of powder for 1.0g liquid at the manufacturer's recommended ratio; (3) 30% of the powder was added to the recommended amount of powder for 1.0g liquid at the manufacturer's recommended ratio. The compressive strength and fracture toughness of the glass ionomer cements at 24 hours or 4 weeks after the start of mixing were determined. The compressive strengths of glass ionomers mixed at the highest powder-liquid ratio were greater than those at the lowest powder-liquid ratio, except for one conventional type cement after 4 weeks. The fracture toughness values of the conventional glass ionomers were lower compared to the resin-modified type at each cement mixing ratio. The fracture toughness of the resin-modified glass ionomers was less influenced by the powder-liquid ratio of the cement compared to conventional types. The present study showed a significant correlation between the compressive strength and the fracture toughness except for the conventional glass ionomers at 4 weeks. The mechanical strength of the conventional glass ionomer cements was affected more by the powder-liquid ratio of the cement compared to the resin-modified glass ionomers.

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The aim of this study was to evaluate the Ti-6Al-4V ELI (extra-low interstitial) alloy fabricated in an electron beam melting (EBM) unit for dental applications based on mechanical properties. The cast Ti-6Al-4V ELI (ASTM grade 23) and commercially pure titanium (CP Ti, ASTM grade 2) were used as controls. In the preparation of cast specimens, the specimens were invested using a MgO-based mold and cast in a titanium casting machine. The Ti-6Al-4V ELI fabricated by EBM exhibited a similar strength and ductility to the cast Ti-6Al-4V ELI. In the future, additional characteristics such as accuracy, fatigue behavior, corrosion resistance, and surface morphology should be investigated for possible dental applications of this process.

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We examined the effects of the layering conditions of flowable and conventional paste-composite resins on the mechanical properties and tooth adhesion of the polymerized materials. The Layering conditions of resin were adjusted so that the proportions of flowable and conventional paste-resins were either 25, 50, or 75% of the sample thickness. The flowable resin was set to comprise the lower layer of the sample. Particularly, after thermal cycling and cyclic loading, the layered samples showed a higher modulus of elasticity and bond strength than those of the monolayer flowable resin, and higher flexural strength than that of the conventional paste resin. These results on both the mechanical properties and adhesion durability of polymerized materials suggest that lamination with 50% or lower flowable and conventional paste-resins may be a clinically useful procedure.

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Applications of conventional anatase-type titanium with a band gap of 3.2eV have been confined to industrial uses such as exterior paints and air cleaners because of the absorption of light with a short wavelength below 420nm. We have produced a commercial product of titania with a 2.2eV band gap for dental bleaching. This product irradiated by blue EL has been shown to produce some kinds of radical including super oxide ions, and bleach a model tooth dyed in minocycline as ΔE:+7.2 under irradiation with blue EL light. In this study, it was suggested that this titania for dental bleaching may be applicable as a new material.

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The purpose of this study was to examine the influences of the diameter, number, and arrangement of fiber posts on the bending strength at proportional limits, apparent yield strength, maximal bending strength, and elastic modulus of the composite resin core complex. One kind of composite resin core material and five kinds of fiber post with a different diameter were used as the experimental materials. Composite resin core material was poured into a glass tube with a 3-mm diameter and, additionally, fiber posts under experimental conditions were inserted into the tube, respectively. Then, the complex was cured through light irradiation and tested in a three-point bending machine. The failure mode after the bending test was observed with SEM. The composite resin core material with one fiber post showed a lower apparent yield strength than that with 4 fiber posts. The core material with a single but thicker fiber post and 4 fiber posts showed a higher maximal bending strength than that with one thinner one. No conditions showed a significant difference regarding the proportional limits and elastic modulus compared with only the composite resin material. The failure modes of the core material with one and with 4 fiber posts were different.

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