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Volume 23 (2004)
- Issue 4 Pages 441-
- Issue 3 Pages 251-
- Issue 2 Pages 67-
- Issue 1 Pages 1-
Volume 23, Issue 1
Displaying 1-9 of 9 articles from this issue
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Kazuyoshi KITAHARA, Fuminobu KUBO, Junzo TAKAHASHI2004 Volume 23 Issue 1 Pages 1-7
Published: 2004
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSNew investments for titanium were developed by adding ZrC and ZrN as additives for thermal expansion to an MgO cement base investment with setting shrinkage and low thermal expansion. Setting, thermal and residual expansion, X-ray diffraction and compressive strength of these experimental investments, surface roughness of the cast plate and casting accuracy of titanium crowns were evaluated. Thermal expansion of investments increased with additive amounts, and residual expansion occurred even when cooling to room temperature after firing in an air atmosphere by the oxidation to ZrO2 of these additives. The casting accuracy of full-crowns cast into molds at room temperature correlated with the content of ZrC and ZrN. As the result the cast titanium crown could be obtained with low surface roughness and good adaptability.View full abstractDownload PDF (2807K) -
Zeynep YESIL DUYMUS, Nuran DINÇKAL YANIKOGLU2004 Volume 23 Issue 1 Pages 8-13
Published: 2004
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSThe purpose of this study was to evaluate the influence of a thickness and processing method on linear dimension change and water sorption in a denture base resin after storage in water for 24 hours, one week, and four weeks.
Sixty wax specimens 65mm long and 10mm wide were fabricated in three thicknesses, 1.5, 3, and 4.5mm. Three dimples were made in each wax specimen. A travelling microscope was used to measure the total distance from the uppermost dimple to the lowest dimple to the nearest 0.01mm.
Acrylic resin blocks were polymerized with 2 processing cycles (short and long-cured). Immediately after processing, all samples were measured by the same investigator. They were then weighed by an electronic precision balance capable of measuring to 0.001g.
Data were analyzed by analysis of variance. Thickness and time of storage were statistically significant on the dimensional change (linear and weight changes) of denture-base resin (p<0.01), showing the influence of the processing method.View full abstractDownload PDF (845K) -
Yuji SAITO2004 Volume 23 Issue 1 Pages 14-18
Published: 2004
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSTo explore the feasibility of a new relining material, polymerization characteristics such as peak temperature, setting time, residual monomer, and postpolymerization were examined in ethyl methacrylate (EMA) resins composed of EMA and 4 kinds of EMA/methyl methacrylate (MMA) copolymers with high and low molecular weights and initiated by benzoyl peroxide/N, N-dimethyl-p-toluidine system and compared with those of MMA/PMMA resins. Peak temperature (53.8-71.0°C) and residual monomer (2.56-3.52% after 1h and 1.57-2.31% after 24h) of the EMA resins were significantly lower than those of the MMA resins (88.9-93.4°C and 4.61-5.85% after 1h and 4.09-4.84% after 24h, respectively). The composition of the copolymers had a significant effect on peak temperature and setting time but no significant effect on residual monomer and postpolymerization. The molecular weight of the copolymers affected peak temperature, setting time and residual monomer significantly. This study suggested that EMA resins are worthy of further evaluation as a relining material.View full abstractDownload PDF (812K) -
Fumio TERAOKA, Masafumi NAKAGAWA, Junzo TAKAHASHI2004 Volume 23 Issue 1 Pages 19-23
Published: 2004
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSThe purpose of this study was to investigate the retention force of complete palate coverage and palate-less dentures made with three polymerization systems (DS system, SR-Ivocap system, microwave polymerization system) in vitro. The retention force between each denture and a polyurethane model by intervening artificial saliva was measured using a tensile tester. In addition, discrepancies between the denture base and the stone cast were measured at several points. The retention force of complete palate coverage and palate-less dentures made with the 3 polymerization systems shows that the DS system had a greater retention force than the SR-Ivocap system and the microwave system. Moreover, the retention force of palate-less dentures was greater than that of complete dentures only in the case of the DS system. The interaction of the polymerization system and the denture type also had a statistically significant effect on the retention force. Dentures made with the DS system had smaller discrepancies compared with dentures processed with the other systems. The retention force correlated very closely with discrepancies at the denture border and the residual ridge.View full abstractDownload PDF (2225K) -
Mitsumasa NAGAO, Taiji SOHMURA, Souichirou KINUTA, Tetsuya KOJIMA, Kaz ...2004 Volume 23 Issue 1 Pages 24-30
Published: 2004
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSA system to provide quantitative information on the angle between dentition and face was developed using a three-dimensional (3D) integrated configuration measured by a non-contact 3D digitizer. The integrated configuration angles between the Camper's plane and occlusal plane on the sagittal and the horizontal projected planes were obtained. Clinical application for a patient to improve the tegmenta of the anterior tooth by setting a temporary bridge on her lower dentition was attempted. Her dentition and face were measured on her first visit and after treatment, and 3D data of them were integrated. The quantitative change of the angle between the Camper's plane and lower occlusal plane were successfully analyzed by the present system, and after treatment, rotation of the lower occlusal plane for 1° in a clockwise direction on the sagittal plane projection, and that for 1° in a counterclockwise direction on the horizontal plane projection relative to the Camper's plane were detected.View full abstractDownload PDF (2392K) -
Mansuang ARKSORNNUKIT, Hidekazu TAKAHASHI, Norihiro NISHIYAMA2004 Volume 23 Issue 1 Pages 31-36
Published: 2004
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSThe purpose of this study was to evaluate the effects of the silane coupling agent amount on the flexural properties and hydrolytic durability on an experimental composite resin for understanding the optimum amount of silanation. A spherical filler was silanated with 7 different amounts of γ-MPTS, 0, 0.17, 0.34, 0.66, 1.36, 2.72 and 5.45mass%. Photopolymerized experimental composite resins were made from a 70/30mass% of UDMA/TEGDMA and a 65mass% of different silanated amounts of filler. Bar-shaped specimens were prepared for a 3-point bending test in 37°C water after 1-day water storage at 37°C and after an additional 1, 7, and 28 days hot water storage in Soxhlet's extractor. The flexural strength and flexural modulus of unsilanated filler dramatically decreased after 28 days hot water storage while those of silanated filler showed a slight change. These results suggested that the silanated amount on the silica filler is not sensitive for flexural properties and hydrolytic stability of composite resin.View full abstractDownload PDF (2042K) -
Masafumi KIKUCHI, Osamu OKUNO2004 Volume 23 Issue 1 Pages 37-45
Published: 2004
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSIn the present study, the machinability of titanium, Ti-6Al-4V, Ti-6Al-7Nb, and free-cutting brass was evaluated using a milling machine. The metals were slotted with square end mills under four cutting conditions. The cutting force and the rotational speed of the spindle were measured. The cutting forces for Ti-6Al-4V and Ti-6Al-7Nb were higher and that for brass was lower than that for titanium. The rotational speed of the spindle was barely affected by cutting. The cross sections of the Ti-6Al-4V and Ti-6Al-7Nb chips were more clearly serrated than those of titanium, which is an indication of difficult-to-cut metals. There was no marked difference in the surface roughness of the cut surfaces among the metals. Cutting force and the appearance of the metal chips were found to be useful as indices of machinability and will aid in the development of new alloys for dental CAD/CAM and the selection of suitable machining conditions.View full abstractDownload PDF (3826K) -
Hardness of Titanium CastingsYukun MENG, Akira NAKAI, Shinichi GOTO, Hideo OGURA2004 Volume 23 Issue 1 Pages 46-52
Published: 2004
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSThe Vickers hardness of the cross-sectioned area of titanium castings made from an experimental resin-bonded calcia investment and three commercial investments was evaluated. The microstructure and element distribution of the surface zone were analyzed using an EPMA. The results showed that the high hardness of the casting surface could be decreased using the experimental investment. The hardness of the castings made from the experimental investment at a 25-50μm depth was lower than those from the other investments, and the thickness of the hardened casting surface was 125μm. Layered structures with fewer layers were formed on the surfaces of the castings made from the experimental investment. The layered structures were influenced by both the investment components and the mold temperature at casting. The less contaminating nature of the experimental investment components and the technology of the room temperature mold contributed to the improved surface properties of the resulting castings.View full abstractDownload PDF (2191K) -
Shinichi UKON, Masatugu ISHIKAWA, Monica TOHYAMA, Hironobu SATO2004 Volume 23 Issue 1 Pages 53-62
Published: 2004
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSThis study was performed to find an acceptable internal adaptation of castable ceramics containing mica and β-spodumene crystals. The influences of factors, expansion rate of phosphate-bonded investment (A), anisotropic expansion (B), diecoating (C), shrinkage during crystallization (D), and interaction (A×B), and (A×C) were tested by twice repeated experiments under block design according to L8 (2)7 orthogonal array. Estimated mean ranges under the conditions combined with significant factors were judged by considering the criteria of the ideal internal gap (about 50μm).
The ideal marginal fit of less than 50μm and uniform cement space about 50μm around the axial wall could be achieved by a combination of optimum levels of A1B1C2D2. However, the estimated mean gap at the cusp tip and central fossa of occlusal inside by this combination were about 120μm. The near intolerable gaps could not be reduced.View full abstractDownload PDF (2524K)
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