Person: GÜNDÜZ, OĞUZHAN
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GÜNDÜZ
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OĞUZHAN
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Publication Metadata only Calcium orthophosphates(2008-01-01) GÜNDÜZ, OĞUZHAN; Dorozhkin S., Oktar F., GÜNDÜZ O.Publication Metadata only Sintering effect on mechanical properties of composites of bovine hydroxyapatite (BHA) and Li2O(Trans Tech Publications Ltd, 2006) OKTAR, FAİK NÜZHET; Oktar F.N., Demirer M.R., Gunduz O., Genc Y., Agathopoulos S., Peker I., Ozyegin L.S., Salman S.In this study, hydroxyapatite (HA) material, obtained from calcinated bovine bone (BHA), was mixed with 0.25, 0.50, 1.00, and 2.00 wt% Li 2CO3. The pressed pellets were sintered at various sintering temperatures between 900°C and 1300°C. Measurements of compression strength, microhardness, and density, along with SEM observation and X-ray diffraction analysis were performed. The experimental results showed that the samples with 0.25 and 0.50% Li2CO3. reached a maximum of densification and the highest values of compression strength and microhardness were achieved after sintering at 1300°C. The wetting effect of a Li2O-associated glassy phase was observed even from 900°C.Publication Metadata only Effect of yttria-doping on mechanical properties of bovine hydroxyapatite (BHA)(SAGE PUBLICATIONS LTD, 2008) OKTAR, FAİK NÜZHET; Gunduz, O.; Daglilar, S.; Salman, S.; Ekren, N.; Agathopoulos, S.; Oktar, F. N.Sintered bodies of hydroxyapatite, derived from calcinated bovine bone (BHA) and doped with 0.5 and 1wt% Y2O3, were prepared. Measurements of density, compression strength, and microhardness, along with scanning electron microscopy (SEM) and X-ray diffraction (XRD) were carried out. The experimental results showed that BHA doping with yttria favors formation of glassy phase, which advances sintering and results in a dense and reinforced BHA matrix. The best mechanical properties were achieved after sintering at 1200 degrees C for compressive strength (82 MPa) and 1300 degrees C for microhardness (672 HV). These results are better than pure BHA or composites of hydroxyapatite with Y2O3-stablized zirconia, qualifying yttria (as dopant of BHA) for further in vitro and in vivo experimentation.Publication Open Access Biomechanical comparison of a new technique of mandibular angle fractures: Biplanar and bicortical superior proximal 3 holes and bicortical inferior plate fixation(2008-01-01) GÜNDÜZ, OĞUZHAN; Turgut G., Kayali M., Soydan A., Gündüz O., Salman S., Oktar F., Baş L.Miniplates have been used for mandibular angle fractures during the past 2 decades. The technique of placing single miniplate at the upper border based on the tension lines of the fracture was proposed by Michelet and Champy. The need for a second miniplate to be applied to the lower mandible has been discussed recently. Biomechanical comparison of biplanar and monoplanar dualminiplate fixation techniques was investigated by Haug. Our hypothesis is in dual-miniplate fixation; the proximal 3 holes of superior border miniplate could be fixated by bicortical screws. The first 2 are at the proximal bone segment and are not related to the tooth and also superior to the alveolar nerve. Generally, the third molar tooth is extracted because it is at the fracture site. Hence, the proximal third hole could also be fixated by bicortical screws. We define a biplanar dual-miniplate technique in which the lower plate and the proximal 3 holes of the upper plate are fixated by bicortical screws. We have designed a study for biomechanical comparison of our method and popular types of mandibular fixation methods.Publication Metadata only Mechanical properties of bovine hydroxyapatite (BHA) composites doped with SiO2, MgO, Al2O3, and ZrO2(SPRINGER, 2007) GÜNDÜZ, OĞUZHAN; Oktar, Faik Nuezhet; Agathopoulos, Simeon; Ozyegin, L. Sevgi; Gunduz, Oguzhan; Demirkol, Nermin; Bozkurt, Yahya; Salman, SerdarBiologically derived hydroxyapatite from calcinated (at 850 degrees C) bovine bones (BHA) was doped with 5 wt% and 10 wt% of SiO2, MgO, Al2O3 and ZrO2 (stabilized with 8% Y2O3). The aim was to improve the sintering ability and the mechanical properties (compression strength and hardness) of the resultant BHA- composites. Cylindrical samples were sintered at several temperatures between 1,000 and 1,300 degrees C for 4 h in air. The experimental results showed that sintering generally occurs at 1,200 degrees C. The BHA-MgO composites showed the best sintering performance. In the BHA-SiO2 composites, extended formation of glassy phase occurred at 1,300 degrees C resulting in structural degradation of the resultant samples. No sound reinforcement was achieved in the case of doping with Al2O3 and zirconia probably due to the big gap between the optimum sintering temperatures of BHA and these two oxides.Publication Metadata only Sintering effect on mechanical properties of composites of natural hydroxyapatites and titanium(ELSEVIER SCI LTD, 2009) OKTAR, FAİK NÜZHET; Salman, S.; Gunduz, O.; Yilmaz, S.; Ovecoglu, M. L.; Snyder, Robert L.; Agathopoulos, S.; Oktar, F. N.This study presents the fabrication and characterization of composite materials of hydroxyapatite and Ti. Hydroxyapatite (HA) powder was obtained from bovine bones (BHA) and human enamel (EHA) via calcination technique. Fine powders of HA were admixed with 5 and 10 wt.% fine powder of metallic Ti. Powder-compacts were sintered at different temperatures between 1000 and 1300 degrees C. Compression strength, Vickers microhardness and elastic modulus as well as density were measured. SEM and X-ray diffraction studies were also conducted. The experimental results showed that addition of Ti to EHA and BHA decreases the elastic modulus, comparing to samples of pure BHA. The best mechanical properties for BHA-Ti composites were obtained after sintering in the range of 1200-1300 degrees C and for EHA-Ti composites in the range of 1100-1300 degrees C. (C) 2009 Elsevier Ltd and Techna Group S.r.l. All rights reserved.Publication Metadata only Sintering effect on mechanical properties of composites of enamel derived hydroxyapatite (EHA) and titanium(Trans Tech Publications Ltd, 2006-05-15) OKTAR, FAİK NÜZHET; Gunduz O., Oktar F.N., Oz B., Altundal H., Agathopoulos S., Salman S., Ovecoglu L.Hydroxyapatite (HA) is one of the most promising biomaterials, which is on use since decades in biomedicine. Because of the known mechanical weakness of HA in load carrying situations, various dopants, like ceramic oxides and metallic particles, have been used to produce HA-composite materials. In this study, Ti powders were admixed with enamel derived HA at 5 and 10 wt %. After ball milling, the mixtures were uniaxially pressed into pellets of a cylindrical form. The composites were sintered at temperatures between 1000°C and 1300°C. Microhardness, compression strength, and density measurements together with X-ray diffraction analysis and SEM studies were performed. The best mechanical values were obtained for the samples sintered between 1100°C and 1300°C.Publication Metadata only Reinforcing of Biologically Derived Apatite with Commercial Inert Glass(SAGE PUBLICATIONS LTD, 2009) OKTAR, FAİK NÜZHET; Gunduz, O.; Ahmad, Z.; Ekren, N.; Agathopoulos, S.; Salman, S.; Oktar, F. N.Apatite-based ceramics, derived from fine powder of calcinated bovine-bone (BHA), were successfully reinforced with 5 and 10 wt% commercial inert glass (CIG), which contained biocompatible elements, via sintering at different temperatures between 1000 and 1300 degrees C. The products were subjected to mechanical testing and microstructural and crystallographic analyses. Comparison of the experimental results with those from earlier similar studies shows that CIG is superior for reinforcing of BHA ceramics compared with other bioactive glasses. Provided that the CIG addition does not exceed a certain limit, optimally being approximately 5 wt%, the resultant BHA-CIG materials can exhibit high strength after sintering and remarkable resistance toward over-firing at 1300 degrees C. The influence of the amount of CIG on the developed microstructure and crystalline structure after sintering at different temperatures is discussed.Publication Metadata only Water resistance of bone-cements reinforced with bioceramics(ELSEVIER SCIENCE BV, 2007) OKTAR, FAİK NÜZHET; Daglilar, S.; Erkan, M. E.; Gunduz, O.; Ozyegin, L. S.; Salman, S.; Agathopoulos, S.; Oktar, F. N.The water absorption behavior of bone-cements of PMMA reinforced with 1.5 wt.%, 2.5 wt.%, and 3.5 wt.% silane-treated powders of hydroxyapatite (synthetic, or derived from bovine bones, or teeth enamel), beta-tricalcium phosphate (TCP), bioactive glass (45S5), and zirconia, was investigated. The experimental results showed that addition of calcium phosphate in the polymeric matrix favors water absorption except in the case of enamel hydroxyapatite. Water uptake is also suppressed when 45S5-bioglass or zirconia is added. The solubility is not affected by addition of hydroxyapatite or 45S5-bioglass but it increases when beta-TCP or zirconia is added. A superior behavior of bone-cements reinforced with bioglass-45S5 and enamel hydroxyapatite can be suggested. (c) 2006 Elsevier B.V. All rights reserved.Publication Metadata only Sintering effect on mechanical properties of composites of bovine derived hydroxyapatite (BHA) with titanium(Trans Tech Publications Ltd, 2006) OKTAR, FAİK NÜZHET; Ozyegin L.S., Gunduz O., Oktar F.N., Oz B., Agathopoulos S., Salman S., Ovecoglu L.The aim of this study was to prepare high performance biomaterials suitable for use at load bearing applications with high bioactivity. The hydroxyapatite (HA) was prepared from bovine bones via calcination technique. The bovine derived HA (BHA) was mixed with 5 and 10 wt% metallic titanium (Ti) and the obtained homogenous mixtures were pressed to produce the test samples. The compacts were sintered at temperatures between 1000 and 1300°C. Compression strength, density, and microhardness were measured. SEM and X-ray diffraction studies were also made. The best mechanical properties were obtained between after sintering at 1200-1300°C.