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Light-curing polyethyl methacrylate (PEMA)-urethane dimethacrylate (UDMA) resins and polymethyl methacrylate (PMMA)-UDMA resins were prepared by two processes. For first step, PEMA or PMMA powders were fully dissolved in ethyl methacrylate (EMA) or methyl methacrylate (MMA) and then the PEMA-EMA/PMMA-MMA mixtures were mixed with UDMA. The flexural properties of cured PEMA-UDMA and PMMA-UDMA polymers were measured using two PEMA (Mw: 300,000-400,000 and 650,000-1,000,000) and three PMMA (Mw: 30,000-60,000, 350,000 and 650,000-1,000,000) powders with different molecular weight, four mixing ratios of PMMA-MMA, and three mixing ratios of PMMA-MMA mixture and UDMA oligomer. Polymers with PMMA(Mw: 350,000) MMA=25/50, and with PMMA(Mw: 350,000)-MMA/UDMA=1/2 and =1/1, showed no-fracture in a flexural test at 1 mm/min and flexural strength and flexural modulus showed no significant difference compared with those of commercially available heat- and self-curing acrylic resins (p>0.01). Within limitation of this investigation, methyl methacrylate-UDMA blend polymer of this composition is available for denture base resin.

The purpose of this study was to investigate the apparent viscosities and mechanical properties of two experimental light-curing soft lining materials (SLM-1 and SLM-2) based on soft-type urethane oligomers, as well as the shear bond strength and dye penetration between the denture base resin and the polymerized SLMs after storage in water. The apparent viscosities of SLM-1 and SLM-2 were 144.0-146.9 and 1.9 Pa x s respectively. After storage in water for two prescribed periods (one day and three months), the mechanical properties of the SLMs on the overall were 10.6-20.6 MPa for elastic modulus, 69.3-72.1 for hardness, and 3.8-4.0 MPa for adhesive strength. Tensile strength was observed to decrease after three months' storage in water, when compared to that after one-day storage (p < 0.01). Water sorption rates also differed significantly (p < 0.05)--namely 3.0 and 2.8 mg/cm2 for SLM-1 after one day and three months respectively, and 2.0 and 2.2 mg/cm2 for SLM-2. As for dye penetration, no infiltration was observed at the denture base resin-SLM interface after three months' storage. Based on the results of this study, it seemed like the SLMs possess many suitable properties for use with a new technique that we recently developed for preparing denture base resin and soft lining material.

目的: 本研究では, 新規に開発された反応性有機質複合フィラー含有硬質レジン人工歯の審美的性質を評価する目的で, 色素浸漬試験による色調変化を従来の硬質レジン人工歯と比較した.方法: 実験には, 新規硬質レジン人工歯デュラクロスフィジオ (以下DPとする) と4種類の市販硬質レジン歯を用いた. 試験片は, 義歯技工ステップを加えた場合と加えない場合の2種類の条件で作製した. 完成した試験片は, 0, 5, 000, 10, 000回のいずれかの回数の水中熱サイクルを負荷してから, カレー溶液あるいは塩基性フクシン溶液中に一定時間浸漬した後, 色調変化を測定した. また, カレー溶液色素浸漬試験では, 浸漬後の試験片を蒸留水中に保管した場合の色調を測定して, 色調の回復程度を観察した. また, 色素浸漬試験前後の人工歯の表面性状を走査電子顕微鏡で観察した.結果: カレー溶液浸漬後, 新規人工歯DPはほかの人工歯と同様に着色が認められたが, その程度は小さかった. また, 蒸留水保管3日後における色調回復の程度は, DPが最も大きかった. 塩基性フクシン溶液浸漬後でも, DPの色調変化は, ほかの2種類の人工歯より小さかった.結論: 新規硬質レジン人工歯DPは, 従来の硬質レジン人工歯よりも着色しにくいことが明らかになった. また, 義歯の洗浄を徹底することによって, 義歯使用中の着色を防止できる可能性が示された.

The shear bonding strengths of a veneering resin to polished, sandblasted, and retention bead-cast commercially pure titanium (cpTi) plates with and without alkaline treatment were measured before and after thermal cycling. The bonding strengths to polished cpTi with and without alkaline treatment decreased remarkably with thermal cycling (p0.01). The bonding strength to sandblasted cpTi with alkaline treatment at 5,000 thermal cycles showed no significant differences from those before thermal cycling (p0.05), and those at 20,000 thermal cycles showed values which were quite small (p0.01). On the other hand, there were no significant differences in the bonding strengths of veneering resin to retention bead-cast cpTi in all conditions (p0.05). These results suggested that although alkaline treatment is a simple and effective surface modification technique for titanium improving adhesion to resin due to formation of tight-fine rutile particles, it does not provide sufficient bonding durability for long-period restorations.

Purpose : A new device was made that can produce a high-speed jet of either water (water jet) or abrasives mixed with water (abrasive jet). This paper reports on the ability of this device to remove investment and metal oxides from cast alloy surfaces.Materials and Methods : Two gypsum blocks, three investment blocks before and after heating, and three cast metal plates were tested with the newly produced device. The pressure of the jet was 4 or 8 MPa, and two types of abrasives (#400 and #1500 SiC and glass beads) were used. After treatment, the surface quality was observed with a charge coupled device camera. The concave depths of the investments were measured with a laser displacement meter and the alloy surfaces evaluated with a surface texture measuring apparatus. The concave depths of the investments and the surface roughness (Ra) were statistically analyzed with two-way ANOVA and Tukey's test using data from ten points.Results : After heating, the investment was removed by a 4 MPa water jet ; the concave depth of the investments was from 0.7 to 8.2 mm. The gypsum was removed by the abrasive jet. The oxide films were removed by the 4 MPa abrasive jet using the abrasive agents.Conclusion : This study examined the potential use of a new laboratory tool. It demonstrated that a water jet could remove investment after heating. Gypsum, adhered investment, and metal oxide were removed with an abrasive jet. This new device can be used effectively as a laboratory tool for removal of unwanted surface materials.

To investigate the influence of disinfectant solution on the surface of gypsum, 3% glutaraldehyde, 10% formaldehyde, and water were prepared and surface roughness was observed by SEM.The results were as follows:1. Immersion in any solution greatly damaged the surface of set gypsums, and surface roughness increased.2. It was suggested that immersion in solution for a considerably long time makes the surface rougher, because there was no significant difference between immersing in disinfectant solution and in water which wasused as a control.3. SEM views showed that gypsum crystals which were grown on an acrylic plate were washed away, and gypsum crystal projections were created. Gypsum crystal on part of the surface of the set gypsum, which was immersed in glutaraldehyde and formaldehyde, was destroyed.

A direct retainer's arm is placed on an abutment tooth when an edentulous space is restored by the prosthetic treatment with a removable partial denture. Few analyses, however, have been reported about the effects of retainers on the abutment teeth when the denture base rotates toward and away from an edentulous ridge. A lower second premolar tooth was focused on, and the effects of an extracoronal direct retainer's arm to the periodontal ligament of the abutment tooth were analyzed utilizing the three-dimensional finite element techniques.The results were as follows:1. In case the retentive force is located on one side of a tooth and the reciprocal force on the other side, 1) the smallest von Mises stress (relative stress) on periodontal membrane was observed when the reciprocal force appears on the survey line rather than on the proximal surface, on the proximal-buccal corner and on the proximal-lingual corner, 2) and when the value of the reciprocal force is one-third of the retentive force, reciprocal force works appropriately.2. The proper retentive force is suggested to be lower than 205 g, considering the yield stress of periodontal membrane.3. It is desirable to make the guiding plane which limits the take-off direction of the denture by producing the reciprocal force on the neck of the retainer's arms when they are located on both sides of atooth.

Direct retainer's arm is placed on an abutment tooth when an edentulous space is restored by prosthetic treatment with a removable partial denture. Various attempts have been made to investigate the effects of the retainer of a partial denture on an abutment tooth during functional loading. However, no analysis seems to have been reported about the effects of retainers on the abutment teeth when the denture base rotates toward and away from an edentulous ridge. Attention was paid to the lower second premolar tooth, and the three-dimensional finite element method was used.The results were as follows:1. When only a retentive force was applied, the von Mises stress in the periodontal ligement increased.2. When both retentive and reciprocal forces were properly applied, the von Mises stress in the periodontal ligament was less than that with the retentive force only.3. When both retentive and reciprocal forces were properly set, and a reciprocal force was one-third of a retentive one, the value of the von Mises stress was within 2.4 MPa. Thus, it was suggested that the reciprocation effectively released the stress in the periodontal ligament of an abutment tooth.4. Effective factors for stress relaxation of the periodontal ligament were suggested to exist in the design of a retainer's arm.

The effects of resin-bonded bridge design parameters (adhesive area, shape and metal frame thickness) on the bonding strength of the resin-bonded bridge were investigated by using the adhesion test when the resin-bonded bridge of the upper anteriors was designed as a prerequisite. The adhesion test was performed using a universal testing machine to test the bond strength and toughness of specimensmade with a metal frame bonded to an abutment metal mold.The results were as follows:1. Maximum bonding force (bf) increased as the metal frame thickness (tm) increased. The values of the maximum bonding force were 10-13 kgf for tm 0.5 mm, 34-46 kgf for tm 1.0 mm, and 68-84 kgf for tm=1.5 mm.2. Maximum bonding strength, in which bf was divided by the adhesive area, increased as the adhesive area increased.3. The durability of the resin-bonded bridge was discussed by comparing the toughness. The toughness increased as the metal frame thickness (tm) increased. The values of toughness were 4-13 kgf · mm for tm= 0.5 mm, 10-31 kgf · mm for tm= 1.0 mm, and 20-44 kgf · mm for tm =1.5mm.4. In order to increase the durability of the resin-bonded bridge, the proposed design conditions were the metal frame thickness (tm) should be as large as possible and the large adhesive area and/or additional groove and wing form among the design parameters should be especially effective.

Though cast restoration is the major skill to make prosthesis today, sintered metal restoration by brush application is being investigated and has wide possibilities. As metallographic examination, sintered specimens (S) and conventional cast specimens (C) were compared by SEM observation, X-ray mappings and volume of surface roughness. The results were as follows:1. In comparison of surface roughness of polished cutting surfaces after casting, surface roughness C was smaller than S. SEM observation showed few micro pits on the S surface, and there were some spaces which were supposed to be gas holes. While the cutting surface of C was generally rough, the S surface showed brush streaks and indentations which averaged 3μm in depth, in the intergranular area.2. After the corrosion test in aqua regia, both C and S showed corrosion on the polished surface. The intergranular area was corroded on the C surface and showed tortoise-shell pattern, and selective corrosion was observed inside the crystal grain. There were fusions and spaces between alloy grains of S, and the width of the space was smaller than that of C. No element was found in this space by elementary analysis, hence these spaces were empty. As for the results of surface roughness, S was smaller than C.Based on these results, it is suggested that the corrosion resistance of S is superior to that of C from the metallographical point of view.

Purpose The stress relaxation and compressive strength of resin, resin-modified glass ionomer, glass ionomer, polycarboxylate, and zinc oxide eugenol cements were measured to determine the characteristics of these materials after setting. Methods A total of 19 luting cements including 12 permanent cements and 7 temporary cements were used. Cylindrical cement specimens (10mm long and 6mm in diameter) were obtained by chemical setting or light curing. The specimens were stored for 24–36h in water at 37°C and were then used for the stress relaxation and compression tests. The stress relaxation test was carried out using three constant cross-head speeds of 5, 50, and 100mm/min. Upon reaching the preset dislocation of 0.5mm, the cross-head movement was stopped, and the load was recorded for 60s. Fractional stress loss at 1s was calculated from the relaxation curves. The compressive strength and modulus were measured at a cross-head speed of 1mm/min. Data were analyzed with the Kruskal–Wallis test and Holm's test. Results A zinc oxide eugenol cement [TempBOND NX] exhibited the largest fractional stress loss. A resin cement [ResiCem] showed the largest compressive strength, while a glass ionomer cement [HY-BOND GLASIONOMER CX] showed the largest compressive modulus among all tested cements ( p Conclusion The fractional stress loss could not be classified by the cement type. Two implant cements [Multilink Implant and IP Temp Cement] showed similar properties with permanent resin cements and temporary glass ionomer cements, respectively. Careful consideration of the choice of cement is necessary.

Six soft lining materials have been examined (two acrylic, two silicone, one fluoric and one olefin materials) for their viscoelastic properties and surface deterioration caused by using peroxide denture cleansers. All tests have been done on 7.0 mm thickness disk specimens. The viscoelastic properties were investigated using a 10% compression strain and a 40 sec relaxation.From the results, large difference appeared between the various lining materials.1. The relaxation modulus of the acrylic lining materials was easily deteriorated by the denture cleanser compared with the other lining materials.2. The cloudiness of the specimen surface and the variation of light reflectivity in the surface of the silicone and olefin lining materials became larger those of the fluoric lining material.3. Ethanol added as a plasticizer was almost eluted within short period and furthermore the use of denture cleanser increased the elution rate of ethanol.

We investigated the viscosity and mechanical properties of experimental light-curing soft lining materials based on six commercially available urethane (meth)acrylate oligomers. The viscosities of the six oligomers were 1.9, 20.6, 26.8, 144.0, 185.3, and 8803.4 Pa*s at 25 degrees C. Two monomers (ethyl- and butyl-methacrylate) were added at 20 wt% to these oligomers to decrease the viscosity, resulting in viscosity reductions of 0.2 to 13.6 Pa*s for the six oligomers. The mechanical properties (compressive modulus, Shore A hardness, and tensile strength) were measured after two times light-polymerization for 3 min. The addition of the monomers to the oligomers only slightly changed the mechanical properties, in contrast to the large viscosity changes. Based on these results, it appears that the addition of ethyl- or butyl-methacrylate monomers is useful for decreasing the viscosity of experimental light-curing soft lining materials without changing their mechanical properties.