PubMed İndeksli Yayınlar Koleksiyonu / PubMed Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7645
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Article Citation - WoS: 57Citation - Scopus: 61Viewpoints: Feeding Mechanics, Diet, and Dietary Adaptations in Early Hominins(John Wiley and Sons Inc., 2013) Daegling, David J.; Özçivici, Engin; Özçivici, Engin; Ravosa, Matthew J.; Taylor, Andrea B.; Grine, Frederick E.; Teaford, Mark F.; Ungar, Peter S.; 03.01. Department of Bioengineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyInference of feeding adaptation in extinct species is challenging, and reconstructions of the paleobiology of our ancestors have utilized an array of analytical approaches. Comparative anatomy and finite element analysis assist in bracketing the range of capabilities in taxa, while microwear and isotopic analyses give glimpses of individual behavior in the past. These myriad approaches have limitations, but each contributes incrementally toward the recognition of adaptation in the hominin fossil record. Microwear and stable isotope analysis together suggest that australopiths are not united by a single, increasingly specialized dietary adaptation. Their traditional (i.e., morphological) characterization as "nutcrackers" may only apply to a single taxon, Paranthropus robustus. These inferences can be rejected if interpretation of microwear and isotopic data can be shown to be misguided or altogether erroneous. Alternatively, if these sources of inference are valid, it merely indicates that there are phylogenetic and developmental constraints on morphology. Inherently, finite element analysis is limited in its ability to identify adaptation in paleobiological contexts. Its application to the hominin fossil record to date demonstrates only that under similar loading conditions, the form of the stress field in the australopith facial skeleton differs from that in living primates. This observation, by itself, does not reveal feeding adaptation. Ontogenetic studies indicate that functional and evolutionary adaptation need not be conceptually isolated phenomena. Such a perspective helps to inject consideration of mechanobiological principles of bone formation into paleontological inferences. Finite element analysis must employ such principles to become an effective research tool in this context. © 2013 Wiley Periodicals, Inc.Article Citation - WoS: 18Citation - Scopus: 21Genetic Loci That Control the Loss and Regain of Trabecular Bone During Unloading and Reambulation(John Wiley and Sons Inc., 2013) Judex, Stefan; Özçivici, Engin; Donahue, Leah Rae; Özçivici, Engin; 03.01. Department of Bioengineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyChanges in trabecular morphology during unloading and reloading are marked by large variations between individuals, implying that there is a strong genetic influence on the magnitude of the response. Here, we subjected more than 350 second-generation (BALBxC3H) 4-month-old adult female mice to 3 weeks of hindlimb unloading followed by 3 weeks of reambulation to identify the quantitative trait loci (QTLs) that define an individual's propensity to either lose trabecular bone when weight bearing is removed or to gain trabecular bone when weight bearing is reintroduced. Longitudinal in vivo micro-computed tomography (μCT) scans demonstrated that individual mice lost between 15% and 71% in trabecular bone volume fraction (BV/TV) in the distal femur during unloading (average: -43%). Changes in trabecular BV/TV during the 3-week reambulation period ranged from a continuation of bone loss (-18%) to large additions (56%) of tissue (average: +10%). During unloading, six QTLs accounted for 21% of the total variability in changes in BV/TV whereas one QTL accounted for 6% of the variability in changes in BV/TV during reambulation. QTLs were also identified for changes in trabecular architecture. Most of the QTLs defining morphologic changes during unloading or reambulation did not overlap with those QTLs identified at baseline, suggesting that these QTLs harbor genes that are specific for sensing changes in the levels of weight bearing. The lack of overlap in QTLs between unloading and reambulation also emphasizes that the genes modulating the trabecular response to unloading are distinct from those regulating tissue recovery during reloading. The identified QTLs contain the regulatory genes underlying the strong genetic regulation of trabecular bone's sensitivity to weight bearing and may help to identify individuals that are most susceptible to unloading-induced bone loss and/or the least capable of recovering.Article Citation - WoS: 67Citation - Scopus: 82Microhardness and Fracture Toughness of Dental Materials by Indentation Method(John Wiley and Sons Inc., 2005) Şakar-Deliormanlı, Aylin; Şakar Deliormanlı, Aylin Müyesser; Güden, Mustafa; Güden, Mustafa; 03.02. Department of Chemical Engineering; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyThe main objective of this study was to measure the fracture toughness of the human teeth enamel using the microindentation technique and to compare the results calculated from the equations developed for Palmqvist and radial-median cracks. Vickers microhardness measurements of dental ceramic (alumina) and human teeth were performed using indentation fracture method. The fracture toughness of enamel was calculated using different equations reported in the literature. Vickers microhardness of the sintered alumina specimen (98.8% theoretical density) was measured to be 14.92 GPa under 9.8N indentation load. Three equations based on the radial-median cracks were found to be applicable for the fracture toughness determination of the enamel. Results show that indentation fracture method is adequate to measure microhardness and fracture toughness of dental materials. However the calculation of fracture toughness depended on the nature of the cracks and also on the location of the indentation. Therefore, it is necessary to identify the crack profile and to select the appropriate equation for accurate fracture toughness values.Article Citation - WoS: 37Citation - Scopus: 42Effects of Compaction Pressure and Particle Shape on the Porosity and Compression Mechanical Properties of Sintered Ti6al4v Powder Compacts for Hard Tissue Implantation(John Wiley and Sons Inc., 2007) Güden, Mustafa; Çelik, Emrah; Güden, Mustafa; Altındiş, Mustafa; Çetiner, Sinan; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologySintered Ti6Al4V powder compacts potentially to be used in implant applications were prepared using commercially available spherical and angular powders (100-200 mum) within the porosity range of 34-54%. Cylindrical green powder compacts were cold compacted at various pressures and then sintered at 1200 degrees C for 2 h. The final percent porosity and mean pore sizes were determined as functions of the applied compaction pressure and powder type. The mechanical properties were investigated through compression testing. Results have shown that yield strength of the powder compacts of 40-42% porosity was comparable with that of human cortical bone. As compared with previously investigated Ti powder compacts, Ti6Al4V powder compacts showed higher strength at similar porosity range. Microscopic observations on the failed compact samples revealed that failure occurred primarily by the separation of interparticle bond regions in the planes 45 degrees to the loading axis. Effects of compaction pressure and particle shape on the porosity and compression mechanical properties of sintered Ti6Al4V powder compacts for hard tissue implantation.