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1.
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: 549; Downloads: 66
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2.
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: 636; Downloads: 66
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3.
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: 1192; Downloads: 105
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4.
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: 726; Downloads: 63
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5.
Stress analysis of a unilateral complex partial denture using the finite-element method
Aleksandar Todorović, Katarina Radović, Aleksandar Grbović, Rebeka Rudolf, Ivana Maksimović, Dragoslav Stamenković, 2010, original scientific article

Abstract: Different types of dental restorations are used in the treatment of a unilateral, free-end saddle. A unilateral, complex, partial denture is one of the indications for this case of partial edentulousness. Consequently, the aim of this study was to stress test the unilateral complex partial denture model and its parts, under load, when changing the length of the free-end saddle. The stress distribution in canines and the first premolar, as the retention teeth, was examined under the influence of physiological and excessive occlusal forces by moving the point of attack in a distal direction. CATIA software was used for the creation of the 3D, fixed restoration unit model, in real size, with the appropriate supporting structures (canine and first premolar with present crowns, alveola, periodontal space) that are connected by the SD snap-in-latch attachment to the mobile portion of a partial denture. The mobile portion consists of an acrylate-coated metal base with three teeth (second premolar, first and second molars). The stress analysis, using the finite-element method, was performed under the application of physiological loads of 25 N, 50 N, 75 N and 100 N, and excessive loads of 300 N, 500 N and 700 N in the second premolar region, as well as in the first and second molar region. The results of the analysis showed that the largest amount of load under the application of physiological occlusal forces is positioned on the abutment teeth. Excessive forces are borne by the attachment. The stress analysis, performed on the unilateral complex partial denture model, suggested that the obtained stress values are lower than the limit values at which the plastic deformationin the model occurs.
Keywords: enostransko kompleksna proteza, pritrditev SD snap-in-latch, fiziološka obremenitev, prevelika obremenitev, zobotehnika
Published: 10.07.2015; Views: 994; Downloads: 64
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6.
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: 838; Downloads: 59
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7.
Aspects of titanium-implant surface modification at the micro and nano levels
Iva Milinković, Rebeka Rudolf, Karlo Raić, Zoran Aleksić, Vojkan Lazić, Aleksandar Todorović, Dragoslav Stamenković, 2012, original scientific article

Abstract: The shape and chemical composition, as well as the macro- and microtopography, of an implant surface have been studied widely as the major factors that positively influence implant osseointegration. Titanium and titanium alloys have been used extensively over the past 20 years as biomedical materials in orthopedic and dental surgery because of their good mechanical properties, corrosion resistance, no cell toxicity, and very poor inflammatory response in peri-implant tissue, which confirms their high biocompatibility. Their favorable biological performance is attributed to a thin native oxide film that forms spontaneously on the titanium surface. It is well established that surface roughness plays an important role in implant fixation. Accordingly, some authors have indicated the existence of an optimal range of surface roughness. The titanium surface can be either chemically or physically modified, or both, in order to improve biomaterial-tissue integration. Different treatments are used to modify the titanium surface. Hydroxyapatite coatings, preceded or not by acid etching, are used to create a rough, potentially bioactive surface. Oxide blasting treatments, either with or without chemical etching, are used to develop roughsurfaces. Thick oxide films obtained by anodic or thermal oxidation have been used to accelerate the osseointegration process. The ideal microtopography of the surface is still unknown, however, because it is very difficult to associate surface properties with clinical results. As more accurate knowledge is required, several Ti surfaces have been analyzed and the endosseous implant surface modified on the micro level has been thoroughly studied. Additionally, the production of gold (Au) nanoparticles to be added to the micron-scale modified surface has been performed. In this respect, an appropriate overview of our results is given.
Keywords: Ti implant, Au nanoparticles titan alloys, surface modification, microstructure
Published: 10.07.2015; Views: 893; Downloads: 69
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8.
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: 624; Downloads: 83
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9.
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: 689; Downloads: 27
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10.
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: 2022; Downloads: 77
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