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1.
Nanofoils for soldering and brazing in dental joining practice and jewellery manufacturing
Karlo Raić, Rebeka Rudolf, Borut Kosec, Ivan Anžel, Vojkan Lazić, Aleksandar Todorović, 2009, original scientific article

Abstract: This paper describes the development of novel, reactive Al-Au nano-multilayered foils, their possible application in different fields and a discussion of the nano-foils' suitability for dental and jewellery applications. Moreover, this study includes the rapid joining of similar and dissimilar materials, by placing multilayer nano-foils and two layers of solder or braze. The foils precisely control the instantaneous release of heatenergy for the joining and act as a controllable local heat source. The reactive foils' thickness is in the range 10 nm to less than 100 nm and they contain many nanoscale layers that alternate between materials with high mixing heats, such as Al and Au. The foil between the two solder/braze layers melts the solder/braze with the heat generated by the reaction and bonds the components. The use of reactive foils eliminates the need for a furnace and dramatically increases the soldering/brazing heating rate of the components being bonded. Thus, ceramics and metals can be fused over required areas without the thermal stresses that are encountered in furnace soldering or brazing. In addition, a completely new plasma technology is proposed for the manufacturing of nano-foils and the first results of the preliminary experimental testing are presented.
Keywords: ceramic-metal bonding, low-temperature, nano-foils, plasma technology, dentistry, jewellery
Published: 01.06.2012; Views: 1358; Downloads: 59
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2.
In-vitro evaluation of the retention of different prefabricated posts luted with different cements
Miloš Maksimović, Aleksandra Špadijer Gostović, Aleksandar Todorović, Nebojša Romčević, Rebeka Rudolf, Ana Todorović, 2012, original scientific article

Abstract: The aim of this study was to assess and compare the mechanical resistance and the retentive force of metal and composite post systems cemented with different types of cements. Three different designs of prefabricated titanium alloy posts were used in the study, i.e., active, passive and combined, as well as AgPd cast posts and two different fibre-reinforced composite post systems. In accordance with the experimental design these posts were cemented with zinc phosphate, self-curing composite resin or self-adhesive, self-etching, luting agent. Comparing the results between the different metal post designs, cemented with zinc phosphate, a statistically significant difference in the retention was found between all the analysed posts. The best results with the pull-out test were obtained with the active posts, then the passive, followed by the combined posts. The metal cast posts cemented conventionally with Zn-phosphate demonstrated the lowest retentive force value, based on all the measurements. The bond strengths between the post and the root dentine were influenced statistically by the post design (active, passive, combined or cast) and material, metal vs. composite. The active Ti posts showed significantly superior retention in combination with all the cements. The Ti alloy posts achieved higher retentive force values than the composite posts, in general. The composite cements compared to the Zn-phosphate ensure a better retentive strength for all the posts, including individually cast posts.
Keywords: retention, prefabricated titanium posts, fibre-reinforced composite posts, cements, pull-out testing
Published: 10.07.2015; Views: 468; Downloads: 54
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3.
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: 633; Downloads: 54
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4.
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: 510; Downloads: 55
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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: 865; Downloads: 54
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6.
Mechanical properties and microstructure characterisation of Au-Pt dental alloy
Rebeka Rudolf, Tjaša Zupančič Hartner, Ladislav Kosec, Aleksandar Todorović, Borut Kosec, Ivan Anžel, 2008, original scientific article

Abstract: Development of a dental alloy with high Au content is based on the ternary system of Au-Pt-Zn with a nominal composition of 86,9Au-9,9Pt-1,5Zn, and about 1,5 wt.% micro-alloying elements (In, Ir, Rh). The results analyses of different heat-treated states showed that the optimal mechanical properties and hardness of an Au-Pt-Zn alloy can be reached with combinations of heat treatment for 20 minutes at 723 K and then slowly cooling, if the alloy was annealed at 1223 K for 30 minutes and the water quenched. Research results confirmed that the microstructure of the Au-Pt-Zn alloy consists of two phases: α1-phase rich in Au (main phase) and α2-phase rich in Pt (minor phase). During XRD analysis and use of the Rietveld method, it was found that the α1-phase content is about 98,5 wt.% while the content of α2-phase is 1,5 wt.%. STA analyses show that the Au-Pt-Zn alloy has a solidus temperature of about 1292 K and a liquidus temperature of about 1412 K.
Keywords: Au dental alloy, properties, microstructure, characterization
Published: 03.07.2017; Views: 475; Downloads: 61
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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: 772; Downloads: 58
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8.
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: 705; Downloads: 47
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