1. Synthesis of PMMA/ZnO nanoparticles composite used for resin teethDanica Popović, Rajko Bobovnik, Silvester Bolka, Miroslav Vukadinovič, Vojkan Lazić, Rebeka Rudolf, 2017, izvirni znanstveni članek Opis: Wear resistance is one of the most important physical properties of the artificial teeth used in acrylic dentures. The goal of this research was to synthesize a new composite material made of matrix Poly-(methyl methacrylate)-PMMA with different percentages (2 % and 3 % of volume fractions) of zinc-oxide nanoparticles (ZnO NPs) as reinforcing elements, to improve its mechanical properties. The dynamic mechanical behaviour of this composite was studied through the DMA method in comparison to the pure PMMA supported by the characterization of their microstructures. Then the wear resistance was analysed on the samples, which were prepared in the form of teeth. In this context their vertical height loss was measured after 100,000 chewing cycles on a chewing simulator, before and after the artificial thermal ageing. Investigations showed that the PMMA/ZnO NP composites dampened the vibrations better than the pure PMMA, which could be assigned to the homogenous distribution of ZnO NPs in the PMMA matrix. It was found that the mean vertical height loss for the pure PMMA teeth was significantly higher (more than 4 times) compared to composite teeth made with ZnO NPs. Introducing the thermal artificial ageing led to the finding that there was no effect on the height loss by the composite material with 3 % of volume fractions of ZnO NPs. Based on this it was concluded that PMMA/ZnO NPs composites showed improved in-vitro wear resistance compared to acrylic-resin denture teeth, so this new composite material should be preferred when occlusal stability is considered to be of high priority.
Ključne besede: poly-methyl methacrylate, PMMA, zinc-oxide nanoparticles, composite, resin teeth
Objavljeno v DKUM: 12.12.2017; Ogledov: 1244; Prenosov: 413
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2. Mechanical properties of the materials for bruxoguardsVojkan Lazić, Aleksandra Špadijer Gostović, Nebojša Romčević, Igor Đorđević, Ana Todorović, Rebeka Rudolf, 2014, izvirni znanstveni članek Opis: The aim of this study is to investigate the mechanical properties of polymethyl methacrylate (PMMA) and thermoplastic polycarbonate (TPC) materials in order to produce night bruxoguards. For this purpose we used a static tensile test. In the next step the microstructures of PMMA and TPC were observed. Within this framework special attention was paid to the examination of the tensile-test tube fracture surfaces for both materials. This approach revealed that PMMA is a brittle and TPC is a plastic material. Certain mechanical properties and a review of the crucial areas confirmed that the TPC material is extremely favourable for making occlusal splints.
Ključne besede: polymers, mechanical properties, characterization, bruxoguards, polymethyl methacrylate, thermoplastic polycarbonate
Objavljeno v DKUM: 16.03.2017; Ogledov: 1578; Prenosov: 118
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3. Stress-strain analysis of an abutment tooth with rest seat prepared in a composite restorationLjiljana Tihaček Šojić, Aleksandra M Lemić, Dragoslav Stamenković, Vojkan Lazić, Rebeka Rudolf, Aleksandar Todorović, 2011, izvirni znanstveni članek Opis: 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.
Ključne besede: kompozitna opora, oporni zob, porazdelitev napetosti, FEM
Objavljeno v DKUM: 10.07.2015; Ogledov: 1153; Prenosov: 89
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4. Aspects of titanium-implant surface modification at the micro and nano levelsIva Milinković, Rebeka Rudolf, Karlo Raić, Zoran Aleksić, Vojkan Lazić, Aleksandar Todorović, Dragoslav Stamenković, 2012, izvirni znanstveni članek Opis: 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.
Ključne besede: Ti implant, Au nanoparticles titan alloys, surface modification, microstructure
Objavljeno v DKUM: 10.07.2015; Ogledov: 1241; Prenosov: 93
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5. Nanofoils for soldering and brazing in dental joining practice and jewellery manufacturingKarlo Raić, Rebeka Rudolf, Borut Kosec, Ivan Anžel, Vojkan Lazić, Aleksandar Todorović, 2009, izvirni znanstveni članek Opis: 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.
Ključne besede: ceramic-metal bonding, low-temperature, nano-foils, plasma technology, dentistry, jewellery
Objavljeno v DKUM: 01.06.2012; Ogledov: 1822; Prenosov: 96
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6. CFD analysis of exothermic reactions in Al-Au nano multi-layered foilsKarlo Raić, Rebeka Rudolf, Primož Ternik, Zoran Žunič, Vojkan Lazić, Dragoslav Stamenković, Tatjana Tanasković, Ivan Anžel, 2011, izvirni znanstveni članek Opis: 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.
Ključne besede: Au-Al nano-foils, finite volume method, temperature transfer, concentration transfer
Objavljeno v DKUM: 01.06.2012; Ogledov: 1573; Prenosov: 96
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