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- 저자 : Preising, Rudolf (검색결과 8 건)
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Verena Preis,Sebastian Hahnel,Michael Behr,Martin Rosentritt 대한치과보철학회 2018 The Journal of Advanced Prosthodontics Vol.10 No.4
PURPOSE. To investigate the fatigue and fracture resistance of computer-aided design and computer-aided manufacturing (CAD/CAM) ceramic molar crowns on dental implants and human teeth. MATERIALS AND METHODS. Molar crowns (n=48; n=8/group) were fabricated of a lithium-disilicate-strengthened lithium aluminosilicate glass ceramic (N). Surfaces were polished (P) or glazed (G). Crowns were tested on human teeth (T) and implant-abutment analogues (I) simulating a chairside (C, crown bonded to abutment) or labside (L, screw channel) procedure for implant groups. Polished/glazed lithium disilicate (E) crowns (n=16) served as reference. Combined thermal cycling and mechanical loading (TC: 3000×5캜/3000×55캜; ML: 1.2×106 cycles, 50 N) with antagonistic human molars (groups T) and steatite spheres (groups I) was performed under a chewing simulator. TCML crowns were then analyzed for failures (optical microscopy, SEM) and fracture force was determined. Data were statistically analyzed (Kolmogorow-Smirnov, one-way-ANOVA, post-hoc Bonferroni, α=.05). RESULTS. All crowns survived TCML and showed small traces of wear. In human teeth groups, fracture forces of N crowns varied between 1214±293 N (NPT) and 1324±498 N (NGT), differing significantly (P≤.003) from the polished reference EPT (2044±302 N). Fracture forces in implant groups varied between 934±154 N (NGI_L) and 1782±153 N (NPI_C), providing higher values for the respective chairside crowns. Differences between polishing and glazing were not significant (P≥.066) between crowns of identical materials and abutment support. CONCLUSION. Fracture resistance was influenced by the ceramic material, and partly by the tooth or implant situation and the clinical procedure (chairside/labside). Type of surface finish (polishing/glazing) had no significant influence. Clinical survival of the new glass ceramic may be comparable to lithium disilicate.
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The Draft of German Employment Contract Law
Ulrich Preis 한국노동법학회 2009 노동법학 Vol.0 No.32
I come to the end of my presentation. There remains one last question to be answered. And this is the following: Why, in spite of the necessary and indisputable demand for reasonable regulation, could no major reform of our employment contract law be put through in Germany? My immediate answer is a little bit pessimistic: To me it seems that there is a depressing faintheartedness among German politicians which stands in sharp contrast to the unbroken power of the social partners, i.e. of the employers' associations and the trade unions. For decades both sides have been suppressing every single attempt to codify our employment contract law in a fair and well-balanced way. They are reluctant and unwilling to break out of their traditional argumentation patterns and simply refuse to assist in the development of new and innovative solutions. That's why Germany is incapable to reform itself in the central issues of labour and employment legislation. This concerns not only employment contract law, but also the regulation of industrial disputes which is totally left in the hands of the courts. So far, politicians ventured small steps - yet giant leaps are nowhere in sight. I can but state that this way will rather increase than decrease legal disunity and bolster more opacity to the detriment of our country's welfare. Am lover pessimistic? I hope not. The statements which I quoted to you at the beginning of my presentation and the overall support we have received for our draft so far give me some grounds for hope. Other EU member states intensely try to develop further their national labour and employment legislation to properly react to the changing conditions of our globalised economy and an ageing society. The Netherlands and the Scandinavian countries are often given as examples. I strongly believe Germany can make an effort, too, and do so likewise.
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Application of the Murakami Approach for Prediction of Surface Fatigue of Cemented Carbides
Sergejev Fjodor,Kubarsepp Jakob,Preis Irina 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1
The aim of present work is to link geometrical parameter of maximum area of structural defect (proposed by Y. Murakami, 1983) with surface fatigue mechanisms. Determined relations allow making predictions of surface fatigue properties of cemented carbides (WC-Co hardmetal - H15 - 85wt% WC and 15wt %Co, TiC-based cermets - T60/8 - 60wt %TiC and Fe/8wt% Ni and T70/14 - 70wt %TiC and Fe/14wt% Ni) in conditions of rolling contact and impact cycling loading. Pores considered being equivalent to small defects. Three comparative defects conditions are distinguished: surface pore, just below free surface and interior pores. The Vickers hardness of binder (as main responsible for the fracture mechanism of hardmetal and cermets) assumed to be the basis of such assumption. The estimate of this prediction has been done by analyzing the pore sizes using the statistics of extremes. The lower bound of fatigue properties can be correctly predicted by considering the maximum occurring pore size.
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Gas-phase photocatalytic oxidation of acrylonitrile
Krichevskaya, Marina,Joks, Svetlana,Kachina, Anna,Preis, Sergei Korean Society of Photoscience 2009 Photochemical & photobiological sciences Vol.8 No.5
Photocatalytic oxidation (PCO) of acrylonitrile (AN) on titanium dioxide in the gaseous phase was studied. AN readily undergoes photocatalytic degradation in a gas-solid system by using $TiO_2$ Degussa P25. The AN PCO volatile products, visible in the infrared spectra, included nitrogen dioxide, nitrous oxide, carbon dioxide, water, hydrogen cyanide and carbon monoxide. Longer contact time resulted in deeper oxidation of AN with decreasing hydrogen cyanide and increasing nitrogen dioxide content. The effect of temperature increasing from 60 to $130^{\circ}C$ was observed to be slightly negative in terms of AN degradation rate. However, the effect of increased temperature was noticeable in terms of the character and yields of the PCO products: HCN peaks diminished with growing peaks of $NO_2$.
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Rosentritt, Martin,Schumann, Frederik,Krifka, Stephanie,Preis, Verena The Korean Academy of Prosthodonitics 2020 The Journal of Advanced Prosthodontics Vol.12 No.1
PURPOSE. To investigate the influence of crown material (lithium-disilicate, 3Y-TZP zirconia) and abutment type (rigid implant, resin tooth with artificial periodontium) on wear performance of their antagonist teeth and adjacent teeth. MATERIALS AND METHODS. A mandibular left first molar (#36) with adjacent human teeth (mandibular left second premolar: #35, mandibular left second molar: #37) and antagonistic human teeth (maxillary left second premolar: #25, maxillary left first molar: #26, maxillary left second molar: #27) was prepared simulating a section of the jaw. Samples were made with extracted human molars (Reference), crowned implants (Implant), or crowned resin tooth analogues (Tooth). Crowns (tooth #36; n = 16/material) were milled from lithium-disilicate (Li, IPS e.max CAD) or 3Y-TZP zirconia (Zr, IPS e.max ZirCAD, both Ivoclar Vivadent). Thermal cycling and mechanical loading (TCML) in the chewing simulator were applied simulating 15 years of clinical service. Wear traces were analyzed (frequency [n], depth [㎛]) and evaluated using scanning electron pictures. Wear results were compared by one-way-ANOVA and post-hoc-Bonferroni (α = 0.05). RESULTS. After TCML, no visible wear traces were found on Zr. Li showed more wear traces (n = 30-31) than the reference (n = 21). Antagonistic teeth #26 showed more wear traces in contact to both ceramics (n = 27-29) than to the reference (n = 21). Strong wear traces (> 350 ㎛) on antagonists and their adjacent teeth were found only in crowned groups. Abutment type influenced number and depth of wear facets on the antagonistic and adjacent teeth. CONCLUSION. The clinically relevant model with human antagonistic and adjacent teeth allowed for a limited comparison of the wear situation. The total number of wear traces and strong wear on crowns, antagonistic and adjacent teeth were influenced by crown material.
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