The influences of water-soluble compounds and water contents in a self-etching primer on the adhesion between composite resin and teeth were investigated. The self-etching primer was composed of 30 wt% 2-methacryloyloxyethyl phenyl phosphoric acid (Phenyl-P), water-soluble compounds and water. As the water-soluble compounds, 2-hydroxyethyl methacrylate, ethanol and acetone were used. The ratios of water-soluble compounds and water were varied. The bond strengths of composite resin to bovine enamel or dentin were influenced by the kinds of water-soluble compounds used and the water contents in the self-etching primer. The self-etching primer composed of 30 wt% Phenyl-P, 20 wt% ethanol and 50 wt% water gave the highest bond strengths to both enamel and dentin. The stable conformations of Phenyl-P, water-soluble compounds and Phenyl-P/Ca salt were obtained using molecular mechanics calculations. We suggest that the conformations of each compound may influence bond strength.

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The purpose of this study was to clarify the current working condition of casting ring liners. The questionnaire was completed by 56 dentists and 252 dental technicians. The 50 different liners were used and the number of gold alloy and silver-paradium-gold alloy cast liners used was almost equal. We devided the liners into A-group (Rockwool type) 36.8%, B-group (Ceramic fiber low temperature type) 39.0%, C-group (Ceramic fiber standard type) 4.3%, D-group (Ceramic fiber low-standard type) 11.8% and E-group (Kaolin type) 1.9% for the gold alloy cast. The wet-liner method was used by 44.1% of all respondents, the dry-liner method by 33.1% and petrolatum-painted liner method by 21.8%. The use of the liner differed between dentists (mainly petrolatum-painted liner method) and dental technicians (mainly wet-liner method). Only a small number of respondents reported using a cobalt-chromium alloy cast (58) or a titanium and titanium alloy cast (31). In addition of the cobalt-chromium alloy, titanium and titanium alloy casts used, the reported use of the ring-less cast method was 50% and 55%, respectively.

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This study classified casting ring liners using infrared spectroscopy (IR, ATR-method and KBr tablet-method) and wavelength dispersive X-ray (WDX) spectra. Thirty-four casting ring liners were used. Casting ring liners were classified into eight groups by IR and WDX spectra. Nineteen brands were classified into A group (rock-wool type), three brands into B group (ceramic fiber low temperature type), four brands into B-PE group (ceramic fiber low temperature type with polyethylene film), four brands into C group (ceramic fiber standard type), two brands into D group (ceramic fiber low temperature-standard type), no brand into E group (kaolin type), one brand into F group (unknown) and one brand into G group (hydrophilic polymer type).

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By the use of a finite element method and beam theory, a mechanical consideration is presented for orthodontics case where the lower canine and the premolars were used as anchorage and to produce a distal tipping movement of the lower second molar. The orthodontic force induced by a spring with helical loop was calculated by a small deflection beam theory. A vertical elongation force and distal movement were applied to the second molar. Both forces produced distal tipping, but the vertical force produced lingual tipping. The main mechanical effect of the retainer was fixation of the left canine to the left first premolar. By this effect, the forces applied to the anchorage teeth became uniform. Without retainer, as the flexural rigidity (Young's modulus, the moment of inertia) of the fixing wire was larger, the forces applied to the anchorage teeth became more uniform. The same effect was provided by the increase in the width of the bracket. The applied forces to the anchorage teeth were calculated simply by the beam theory.

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Dumbbell types of specimens of Ti-6Al-4V were prepared by casting, and cutting the cast material into rectangular specimens. After both cut surfaces of each specimen were tightly fixed using a jig, they were provisionally jointed by laser. Then proper jointing was carried out using the following three methods ; for group I direct welding by laser, for group II indirect soldering by laser and for group III indirect soldering by TIG arc. Tensile strength in groups I, II, III was estimated to be 30%, 20% and 34% respectively, on the basis of ratios of the specimens to the as cast. Of these groups, group IV had the highest value of tensile strength ; 1132.8 Mpa. These results suggest that heat discharge under TIG was appropriate to gain larger jointing portions. However, operational difficulty in positioning a specimen, as compared to the laser method is a key draw back to using the TIG method. Since the laser method has very good controllability of positioning for welding, it is suitable for jointing specimens in which control of the position-to-position relationship is important.

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The application of the Ti-Ni base alloy to dentistry is expected to utilize its shape memory effect and super-elasticity properties. The transformation temperature changes when part of the nickel in a Ti-Ni alloy is replaced with copper. In this study, the super-elastic property of Ti-Ni alloy in which part of the nickel was replaced with 10 mol% of copper was investigated, and the application of this alloy to dental casting was also examined. The results of this study showed that the super-elasticity of dental casted Ti-Ni-Cu alloy with 10 mol% of replacement copper was good and that this maybe a useful method of reducing the quantity of nickel in Ti-Ni based alloy.

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To investigate the effects of environmental solutions (distilled water, 3 wt% acetic acid, 5 and 30 wt% ethanol) on the lower limit of stress intensity factor (K_<10>) of heat-cured denture base resin, the measurements of both load and crack length were carried out by the constant strain rate (0.01mm/min) test in the three point bending mode using precracked specimens. The fracture surfaces were also observed by digital microscope to obtain information on the crack growth mechanism. As a result, it was found that the K_<10> was as low as about 0.3 Mpam^<1/2> even in distilled water, suggesting that, orally, environmental stress cracking would probably occur due to environmental solutions in food and bevarages. Moreover the K_<10> was further decreased as the concentration of ethanol increased, which suggests that the habit of drinking alcohol may increase the risk of environmental stress cracking. Furthermore, since the fracture surface formed by 30 wt% ethanol solution was quite different from that in lower concentrations, we speculate that there are two different mechanisms of environmental stress cracking in heat-cured denture base resin.

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The aim of this study was to investigate changes in the solubility and disintegration of the glass ionomer cements that occurred from the initial setting up to 24 hours. Two different types (conventional and resin-modified) of glass ionomer cements were mixed at three different mixing ratios. The amount of solubility and disintegration of the cements immersed in water was determined up to 24 hours. The largest amount of solubility and disintegration in the cements was observed at 5 or 10 min after mixing. There was a significant increase in the amount of solubility and disintegration of the conventional cements at the lowest mixing ratio. A different trend in the behavior of the solubility and disintegration was seen between conventional and resin-modified glass ionomer cements in the initial setting period. The amount of the solubility and disintegration of the cements decreased due to the progress in the setting reaction. The mixing ratio of cements also influenced the behavior of the solubility and disintegration in the initial setting period.

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In this study, we examined the antibacterial effect of Ti plates, anodized by discharging in NaCl, NaF or KI solution, on oral bacteria. (Ti-Cl, Ti-F or Ti-I plates, respectively). SEM photographs of the 3 kinds of plates showed different surface topographies. XRD and XPS analysis showed that the treated surface was covered with titanium oxide film. In addition, X-ray fluorescence analysis and XPS analysis revealed that Cl, F and I were incorporated in each surface. Antibacterial examination of all plates showed the antibacterial effect on oral bacteria (8 strains of 8 species), saliva bacteria and dental plaque bacteria. The antibacterial effects decreased, in the order of Ti-Cl, Ti-F and Ti-I. In addition, no reduction of the antibacterial effect of the Ti-Cl plate was observed after immersion in water for 8 weeks. These results suggest that the Ti plates anodized by NaCl, NaF and KI all had sufficient antibacterial effect to control bacterial colonization.

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The aim of this study was to prepare thin hydroxyapatite (HAP) coatings on titanium (Ti) surface using a 2-stage discharging method in an electrolyte. First, a Ti plate was anodic oxidized by discharging in a phosphoric and citric acid solution with supersaturated tri-calcium phosphates. Then, components in the solution were coated to the Ti plate by discharging with a reversed polarity. XRD, FT-IR, XRF and XMA analysis were performed on both anodic oxidized and coated Ti plates to find suitable discharging conditions. Anodic oxide films contained amorphous calcium phosphate ceramics and calcium titanium phosphate. These elements were important to produce HAP coatings without by-products when Ti plates were cathodic treated under discharging. HAP coatings with a thikcness of 5-10 μm adhered tightly to the surface of the Ti plates and were still stable after 28 days in pH 5.0 NaCl solution. These findings suggest that these coatings may be useful to apply osseous implant materials.

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