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Characterisation of a new dental alloy with high Au content
Rebeka Rudolf, Tjaša Zupančič Hartner, Ivan Anžel, Primož Mrvar, Jože Medved, Dragoslav Stamenković, 2007, original scientific article

Abstract: The basis for developing a new dental alloy with high Au content is appropriate chemical composition and manufacturing technology. This new Au dental alloy is based on the ternary system of Au-Pt-Zn with a nominal composition of 88.5Au-8.7Pt-1.5Zn-0.5In-0.4Ir-0.3Rh. The alloy was melted and cast in a vacuum-induction melting furnace in Zlatarna Celje. Casting was followed with subsequent thermo-mechanical treatment (procedures of profile and polish milling, thermal treatment) and cutting-off strips to form a regular shape. The heat treatments of Au alloy samples were carried out in a tube furnace under different temperatures, and over different times. Testing of the new Au dental alloy included examining the initial cast, and the different heat treated conditions of the Au alloy. The optical properties of Au-dental alloy were investigated by means of spectrophotometric colourimetry. Finally the test of cytotoxicity of new Au based dental alloys using standard in vitro assays for testing the biocompatibility with establishing new, more sensitive, in vitro tests on cell lines was done.Osnovo razvoja nove dentalne zlitine z visoko vsebnostjo Au predstavljata pravilna določitev kemijske sestave in tehnologije izdelave. Nova dentalna zlitina temelji na ternarnem sistemu of Au-Pt-Zn z nominalno kemijsko sestavo 88,5Au-8,7Pt-1,5Zn-0,5In-0,4Ir-0,3Rh. Izdelava dentalne zlitine je potekala s pretaljevanjem zelo čistih komponent v vakuumski indukcijski peči v Zlatarni Celje. Temu je sledilo odlivanje taline v ustrezno formo, postopek termo-mehanske obdelave odlitka in razrez zlitine v ustrezno obliko. Toplotna obdelava je bila izvedena pri različnih temperaturah in za različne čase. Testiranje dentalne zlitine je vključevalo določitev lastnosti začetnega stanja in stanja po različnih toplotnih obdelavah. Optične lastnosti dentalne zlitine so bile raziskane s spektro-fotometrično kolorimetrijo. Na novi Au dentalni zlitini so bili narejeni še testi citotoksičnosti z uporabo standardain vitro analize za testiranje biokompatibilnosti z uvajanjem novih, bolj občutljivih in vitro testov na celični liniji.
Keywords: dental alloy, characterisation, microstructure, properties
Published: 31.05.2012; Views: 1252; Downloads: 26
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CFD analysis of exothermic reactions in Al-Au nano multi-layered foils
Karlo Raić, Rebeka Rudolf, Primož Ternik, Zoran Žunič, Vojkan Lazić, Dragoslav Stamenković, Tatjana Tanasković, Ivan Anžel, 2011, original scientific article

Abstract: This work presents the possibility of numerical modelling using Computational Fluid Dynamics (CFD) in the field of nano-foils. The governing equations were solved using a Finite Volume Methodology (FVM). The computational domain was discretized using a uniform Cartesian grid with the appropriate mesh size along the x and y directions employing the corresponding number of grid points. The field variables were discretized at the cell centres and the spatial, as well as the time, derivatives were approximated using the second-order accurate numerical scheme. The time-evolution of the temperature and concentration fields, as well as the atomic diffusion coefficient, will be presented for the appropriate Al-Au nano-foil geometry and boundary conditions.
Keywords: Au-Al nano-foils, finite volume method, temperature transfer, concentration transfer
Published: 01.06.2012; Views: 992; Downloads: 59
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Gold in the past, today and future
Rebeka Rudolf, Maša Anžel, Evgenija Marković, Miodrag Čolić, Dragoslav Stamenković, 2012, review article

Abstract: This paper deals with gold, which is described as a chemical element. Special attention is paid to its physical-chemical properties and, furthermore, where or in what form it can be found in nature. We discuss the role it has played through history and we inform how gold has been developed to the level it has reached today's value. Still more, when gold is broken into nanoparticles, this form could be highly useful for a wide range of processes, including general nanotechnology, electronics manufacturing and the synthesizing of different functional materials. It is important that we know that gold is also used in industry in many engineering applications (contacts in micro-electronics) and medicine (dental alloys, implants).
Keywords: gold, physical-chemical properties, nano-particles, applications
Published: 01.06.2012; Views: 1674; Downloads: 58
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Trends in micrustructural analyses of dental alloys before and after biocompatibility testing
Rebeka Rudolf, Dragoslav Stamenković, 2012, published scientific conference contribution abstract (invited lecture)

Published: 01.06.2012; Views: 557; Downloads: 23
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Determination of stresses and forces on the orthodontic system by using numerical simulation of the finite elements method
Janko Ferčec, Branislav Glišić, I. Šćepan, Evgenija Marković, Dragoslav Stamenković, Ivan Anžel, Jože Flašker, Rebeka Rudolf, 2012, original scientific article

Abstract: This study was addressed to use knowledge about the orthodontic system with numerical simulation of the nite elements method. For the rst time we simulated the stresses on the orthodontic system and, in this manner, calculated the orthodontic force on the tooth. A 3D orthodontic model or orthodontic system was designed resembling moderate crowding in the dental arch with all supporting structures. CATIA V5 computer software was used to set up a model for the orthodontic system and ABAQUS was used for simulation of the stresses on the orthodontic system. Our attention was focused on the stresses on the tooth lateral incisor and its periodontal ligament. The results of the numerical simulation showed complex stresses on the tooth lateral incisor and its periodontal ligament. In this paper is presented a calculation of the orthodontic force acting on the tooth lateral incisor due to the orthodontic wire. This orthodontic force was calculated from the stresses on the bracket. The calculated orthodontic force was in the area which is considered as the optimal orthodontic force for movement of the tooth.
Keywords: okluzija, ortodontski sistem, metoda končnih elementov, ortodonske sile, zobje, malocclusion, orthodontic system, finite elements method, orthodontic force, tooth
Published: 10.07.2015; Views: 388; Downloads: 68
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Stress-strain analysis of an abutment tooth with rest seat prepared in a composite restoration
Ljiljana Tihaček Šojić, Aleksandra M Lemić, Dragoslav Stamenković, Vojkan Lazić, Rebeka Rudolf, Aleksandar Todorović, 2011, original scientific article

Abstract: Placing a composite restoration on abutments for the removable of partial dentures gives favorable aesthetic results with minimal intervention. The objective of this paper is to analyze the stress distribution of a tooth with occlusal rest-seat preparation in the composite and compare it to the biomechanical behavior of an intact tooth, assuming that the stress and strain distribution throughout the intact tooth provides the control scenario. For this finite-element study two different models were designed. The first model was the three-dimensional (3D) model of an intact tooth, and the other one was a 3D model of a tooth with a composite restoration and an appropriate occlusal rest-seat preparation. Load stimulations were performed when the rest was fully seated on its corresponding rest seat and abutment tooth in order to obtain data about the biomechanical behavior of the abutment tooth compared to the intact toothćs stress-distribution pattern. The results of our analyses are presented and analyzed qualitatively. The occlusal loading effect along the sound tooth exhibits a wider high-stress area, localized in correspondence with the occlusal enamel, than the restored teeth. This is due to the rigidity of the enamel. The reduction in the stress values occurs in the composite restoration, which is less rigid. Its lower rigidity allows larger cusp movements. The stress-distribution pattern of the restored tooth with the rest seat showed that introducing an occlusal restoration does not differ from the intact tooth globally, but locally. Our findings indicate that the composite rest-seat restoration absorbs the loading, so reducing the stresses inside the tooth's structure.
Keywords: kompozitna opora, oporni zob, porazdelitev napetosti, FEM
Published: 10.07.2015; Views: 616; Downloads: 35
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Liquid metal/ceramic interfaces in dental practice and jewellery manufacturing
Karlo Raić, Rebeka Rudolf, Aleksandar Todorović, Dragoslav Stamenković, Ivan Anžel, 2010, review article

Abstract: Metal-ceramic fusing has been the essential step in obtaining materials that benefit from both ceramic and metal constituents, i.e. where the combined properties of metal and ceramic layers are desirable. When considering fusing methods, soldering and active metal brazing are the most effective. These processes involve braze melting and flowing between the two pieces of material. In the first part the phenomena occurring on the boundary between the ceramics and the active filler metal during the metal-ceramics joining are discussed. Three interconnected sub-processes are considered: (1) wetting of the ceramic surface, (2) chemical reactions at the interface and (3) diffusion with a moving interface. Then, the appearances at the grain boundary grooves of the ceramic surface are presented as phenomena on the catalytic surface. In the second part, examples from dental practice and jewellery manufacturing are used for comparative analysis. Finally, we discuss the composition and properties of the soldering and brazing alloys used for dental practice and jewellery manufacturing.
Keywords: metal-ceramic bonding, brazing, soldering, dentistry, jewellery
Published: 10.07.2015; Views: 546; Downloads: 43
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Notranja oksidacija mikrolegiranega zlata za medicinske aplikacije
Tjaša Zupančič Hartner, 2016, doctoral dissertation

Abstract: V doktorski disertaciji je obravnavana problematike izdelave mikrolegiranega disperzijsko utrjenega zlata z disperzijo oksidov (La2O3), redko zemeljskega elementa (La) s procesom notranje oksidacije ter študija biokompatibilnosti materiala.. V prvem delu raziskav smo izdelali zlitino Au – 0,5 ut.% La, s postopkom klasičnega litja. Rezultati karakterizacije so pokazali, da že zelo majhna količina mikrolegirnega elementa lantana v zlati zlitini, povzroči tvorbo intermetane faze Au6La, ki pomembno izboljša mehanske lastnosti mikrolegiranega zlata, v primerjavi s čistim zlatom. V drugem delu smo s tehnologijo hitrega strjevanja in valjanja, izdelali trakove z metastabilno mikrostrukturo. S hitrim strjevanjem zlitine Au - 0,5 ut.% La smo dosegli spremembo morfologije strjevanja. Mikrostruktura hitro strjenih trakov sestoji iz zelo finih zrn αAu, s premerom do nekaj mikrometrov ter homogeno razporejeno intermetalno fazo (Au6La), po celotnem preseku traku. Izmerjena trdota trakov je pokazala, da se je v primerjavi z litim stanjem, trdota povečala za skoraj 20 %. Valjane trakove smo rekristalizacijsko žarili in ugotovili, da že majhen dodatek 0,5 % La, zvišuje temperaturo rekristalizacije do 200 K in povzroči rekristalizacijski zastoj. Karakterizacija materiala, je pokazala, da intermetalna faza Au6La v valjanih trakovih tvori neprekinjeno mrežo po mejah zrn, ki dodatno niža hitrost rekristalizacije. Sledila je notranja oksidacija zlitine v litem, valjanem in hitro strjenem stanju. Rezultati notranje oksidacije zlitine v litem ter valjanem stanju so pokazale, da proces notranje oksidacije poteče le po mejah kristalnih zrn z oksidacijo lantana iz intermetalne faze (Au6La). Med tem ko notranja oksidacija hitro strjenih trakov poteče s oksidacijo lantana iz trdne raztopine in tvorbo CNO ter delno po mejah zrn s oksidacijo lantana iz intermetalne faze (Au6La) . Na osnovi rezultatov smo identificirali mehanizem notranje oksidacije in postavili model notranje oksidacije zlitine Au- 0,5 ut.% La, ki rezultira v disperzijskem utrjanju mikrolegirane zlate zlitine v površinskem sloju, kljub temu, da je topnost kisika v kristalni mreži zlata zelo majhna. V zaključni fazi smo potrdili, da je material Au-0,5 ut.% La biokompatibilen, kar daje možnost njegove uporabe v obliki tankih nanosov na medicinske implantate.
Keywords: notranja oksidacija, zlato, zlitine zlato-lantan, biokompatibilnost zlato-lantan zlitin
Published: 05.07.2016; Views: 937; Downloads: 85
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Hydroxyapatite coatings on Cp-Titanium Grade-2 surfaces prepared with plasma spraying
Rebeka Rudolf, Dragoslav Stamenković, Zoran Aleksić, Monika Jenko, Igor Đorđević, Aleksandar Todorović, Vukoman Jokanović, Karlo Raić, 2015, original scientific article

Abstract: Thin hydroxyapatite coatings were produced on Cp-Titanium Grade-2 samples, with new high-voltage pulse-power equipment PJ-100 (Plasma Jet, Serbia) in order to get a more stable implant structure appropriate for further clinical applications. A comparative analysis of differently prepared surfaces of the Cp-Titanium Grade-2 samples was done before the hydroxyapatite was applied. Microstructural observation of the modified hydroxyapatite/implant surface was done using scanning-electron-microscopy imaging and Auger electron spectroscopy, with the aim of detecting the morphology and the elements contained in the new surfaces of the samples. The results confirmed that the surface of Cp-Titanium Grade-2 modified with hydroxyapatite is very similar to the bone structure.
Keywords: Cp-Ti2 material, hydroxyapatite, plasma, characterization
Published: 16.03.2017; Views: 431; Downloads: 42
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Rhodium platings
Rebeka Rudolf, Bojan Budić, Dragoslav Stamenković, Miodrag Čolić, Andrej Ivanič, Borut Kosec, 2013, short scientific article

Abstract: Modern rhodium plating solutions are based on either sulphate or phosphate. Although in theory there are four possible combinations, in practice only three different rhodium electrolytes are used. These are based on dilutions of rhodium sulphate or phosphate concentrates with added sulphuric or phosphoric acid. These processes are be discussed in this paper with a demonstration of Rh platings in the Slovenian firm Zlatarna Celje d.d.
Keywords: rhodium, plating, jewellery, properties
Published: 03.07.2017; Views: 356; Downloads: 48
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