Examinando por Materia "Hardness"
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Ítem Bone regeneration and docking site healing after bone transport distraction osteogenesis in the canine mandible(W.B. Saunders Ltd, 2012-01-01) Nagashima, L.K.; Rondon-Newby, M.; Zakhary, I.E.; Nagy, W.W.; Zapata, U.; Dechow, P.C.; Opperman, L.A.; Elsalanty, M.E.; Nagashima, L.K.; Rondon-Newby, M.; Zakhary, I.E.; Nagy, W.W.; Zapata, U.; Dechow, P.C.; Opperman, L.A.; Elsalanty, M.E.; Universidad EAFIT. Departamento de Ingeniería de Producción; Materiales de IngenieríaPurpose: Bone transport distraction osteogenesis provides a promising alternative to traditional grafting techniques. However, existing bone transport distraction osteogenesis devices have many limitations. The purpose of this research was to test a new device, the mandibular bone transport reconstruction plate, in an animal model with comparable mandible size to humans and to histologically and mechanically examine the regenerate bone. Materials and Methods: Eleven adult foxhounds were divided into an unreconstructed control group of 5 animals and an experimental group of 6 animals. In each animal, a 34-mm segmental defect was created in the mandible. The defect was reconstructed with a bone transport reconstruction plate. Histologic and biomechanical characteristics of the regenerate and unrepaired defect were analyzed and compared with bone on the contralateral side of the mandible after 4 weeks of consolidation. Results: The reconstructed defect was bridged with new bone, with little bone in the control defect. Regenerate density and microhardness were 22.3% and 42.6%, respectively, lower than the contralateral normal bone. Likewise, the anisotropy of the experimental group was statistically lower than in the contralateral bone. Half the experimental animals showed nonunion at the docking site. Conclusion: The device was very stable and easy to install and activate. After 1 month of consolidation, the defect was bridged with new bone, with evidence of active bone formation. Regenerate bone was less mature than the control bone. Studies are underway to identify when the regenerate properties compare with normal bone and to identify methods to augment bone union at the docking site. © 2012 American Association of Oral and Maxillofacial Surgeons.Ítem Bone regeneration and docking site healing after bone transport distraction osteogenesis in the canine mandible(W.B. Saunders Ltd, 2012-01-01) Nagashima, L.K.; Rondon-Newby, M.; Zakhary, I.E.; Nagy, W.W.; Zapata, U.; Dechow, P.C.; Opperman, L.A.; Elsalanty, M.E.; Universidad EAFIT. Departamento de Ingeniería Mecánica; Bioingeniería GIB (CES – EAFIT)Purpose: Bone transport distraction osteogenesis provides a promising alternative to traditional grafting techniques. However, existing bone transport distraction osteogenesis devices have many limitations. The purpose of this research was to test a new device, the mandibular bone transport reconstruction plate, in an animal model with comparable mandible size to humans and to histologically and mechanically examine the regenerate bone. Materials and Methods: Eleven adult foxhounds were divided into an unreconstructed control group of 5 animals and an experimental group of 6 animals. In each animal, a 34-mm segmental defect was created in the mandible. The defect was reconstructed with a bone transport reconstruction plate. Histologic and biomechanical characteristics of the regenerate and unrepaired defect were analyzed and compared with bone on the contralateral side of the mandible after 4 weeks of consolidation. Results: The reconstructed defect was bridged with new bone, with little bone in the control defect. Regenerate density and microhardness were 22.3% and 42.6%, respectively, lower than the contralateral normal bone. Likewise, the anisotropy of the experimental group was statistically lower than in the contralateral bone. Half the experimental animals showed nonunion at the docking site. Conclusion: The device was very stable and easy to install and activate. After 1 month of consolidation, the defect was bridged with new bone, with evidence of active bone formation. Regenerate bone was less mature than the control bone. Studies are underway to identify when the regenerate properties compare with normal bone and to identify methods to augment bone union at the docking site. © 2012 American Association of Oral and Maxillofacial Surgeons.Ítem Chemical, structural and mechanical characterization of bovine enamel(PERGAMON-ELSEVIER SCIENCE LTD, 2020-01-01) Arango-Santander S.; Montoya C.; Pelaez-Vargas A.; Ossa E.A.; Arango-Santander S.; Montoya C.; Pelaez-Vargas A.; Ossa E.A.; Universidad EAFIT. Departamento de Ingeniería de Producción; Materiales de IngenieríaObjective: The purpose of this investigation was to establish microstructure, microhardness, fracture toughness, chemical composition, and crack repair of bovine enamel and to compare these features with their human counterparts. Design: Bovine enamel fragments were prepared and optical microscopy and atomic force microscopy were used to establish microstructure; Raman spectroscopy was used to estimate composition and microindentation using Vickers testing was performed to evaluate hardness. Results: A strong dependence between indentation load and microhardness values was observed, as was the case in human enamel. Similar microstructure and chemical composition between bovine and human enamel, 7.89% lower microhardness and 40% higher fracture toughness values for bovine enamel were found. Conclusion: From a structural and mechanical standpoint, bovine enamel is a suitable alternative to human enamel for in vitro testing of dental products. © 2019 Elsevier LtdÍtem Effect of aging on the microstructure, hardness and chemical composition of dentin(PERGAMON-ELSEVIER SCIENCE LTD, 2015-12-01) Montoya, C.; Arango-Santander, S.; Peláez-Vargas, A.; Arola, D.; Ossa, E.A.; Montoya, C.; Arango-Santander, S.; Peláez-Vargas, A.; Arola, D.; Ossa, E.A.; Universidad EAFIT. Departamento de Ingeniería de Producción; Materiales de IngenieríaObjective: Understanding the effects of biological aging on human tissues has been a topic of extensive research. With the increase in healthy seniors and quality of life that topic is becoming increasingly important. In this investigation the effects of aging on the microstructure, chemical composition and hardness of human coronal dentin was studied from a comparison of teeth within ``young'' and ``old'' age groups. Methods: The microstructure of dentin within three regions (i.e., inner, middle and outer) was analyzed using electron and optical microscopy. The mineral-to-collagen ratio in these three regions was estimated using Raman spectroscopy and the hardness was evaluated using microindentation. Results: Results showed that there were significant differences in tubule density, tubule diameter and peritubular cuff diameter with depth. Although there was no difference in tubule density and diameter of the tubules between the age groups, there was a significant difference in the occlusion ratio. A significant increase in hardness between young and old patients was found for middle and outer dentin. An increase in mineral-to-collagen ratio from inner to outer dentin was also found for both groups. In old patients, an increase in mineral content was found in outer coronal dentin as a consequence of tubule occlusion. Conclusions: An increase in occlusion ratio, hardness, and mineral content was found in the dentin of adult patients with age. This increase is most evident in the outer coronal dentin. (C) 2015 Elsevier Ltd. All rights reserved.Ítem Hardness of thermal sprayed coatings: Relevance of the scale of measurement(ELSEVIER SCIENCE SA, 2015-04-25) Chicot, D.; Ageorges, H.; Voda, M.; Louis, G.; Ben Dhia, M.A.; Palacio, C.C.; Kossman, S.; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)The coatings obtained by thermal spraying can present a large variety of geometrical parameters (thickness, roughness...), of microstructures (constituents, nature of phases...), of mechanical properties (hardness, elastic modulus...) and of morphological defects (cracks, pores...) depending on the spraying conditions. In order to determine the mechanical properties of the coating, one of the most relevant techniques is probably the instrumented indentation test. Nowadays this technique is very attractive since it allows the determination of numerous parameters. Moreover, recent developments allow the use of a phenomenological approach and modeling at different scales of measurement, from nano (even ultra-nano) to macro scale, i.e. from few milligrams to several kilograms of loading. However, the information, which can be extracted at the different regimes of loading can be the same or lead to different values of the mechanical properties, which can be complementary or contradictory depending on the nature of the coating and the preparation of the sample. For example, roughness, porosity and cracks present in the coating will affect the mechanical characterization since the indentation data analysis is based on how a rigid indenter penetrates into the material. So, an important question arises: Should the influence of these defects to be taken into account, or neglected, for the mechanical characterization? The present work proposes different methodologies for determining the hardness of coated materials by considering or not the influence of both the porosity and roughness of the surface. In the first part, results of microindentation experiments performed on the rough surface of alumina coatings are compared to those obtained on a polished cross-section. Although the surface of the cross-section is irregular even after caution polishing, the hardness can be measured. A decrease of about 30% of the hardness number on the cross-section is observed. The second part is related to the microstructured yttria-stabilized zirconia analysis. A methodology based on the indentation size effect analysis is presented to avoid the influence of roughness and the defects, which can be crossed by the indenter during the indentation. This methodology allows the hardness determination of the coating exempt of defects. In the last part, a statistical analysis using nanoindentation data resulting from the continuous stiffness measurement mode applied to nanostructured yttria-stabilized zirconia shows that, even if the hardness number varies to a great extent according to the applied load and the location of the indent, the hardness can be represented by means of a unique hardness number independent of the sense of the hardness variation during the indenter displacement. (C) 2014 Elsevier B.V. All rights reserved.Ítem Indentation damage and crack repair in human enamel.(ELSEVIER SCIENCE BV, 2013-05-01) Rivera C; Arola D; Ossa A; Rivera C; Arola D; Ossa A; Universidad EAFIT. Departamento de Ingeniería de Producción; Materiales de IngenieríaTooth enamel is the hardest and most highly mineralized tissue in the human body. While there have been a number of studies aimed at understanding the hardness and crack growth resistance behavior of this tissue, no study has evaluated if cracks in this tissue undergo repair. In this investigation the crack repair characteristics of young human enamel were evaluated as a function of patient gender and as a function of the distance from the Dentin Enamel Junction (DEJ). Cracks were introduced via microindentation along the prism direction and evaluated as a function of time after the indentation. Microscopic observations indicated that the repair of cracks began immediately after crack initiation and reaches saturation after approximately 48 h. During this process he crack length decreased up to 10% of the initial length, and the largest degree of reduction occurred in the deep enamel, nearest the DEJ. In addition, it was found that the degree of repair was significantly greater in the enamel of female patients.Ítem Mechanical properties study for new hypothetical crystalline phases of ReB2: A computational approach using density functional theory(Elsevier, 2016-09-01) Marín-Suárez, M.; Vélez, M.E.; David, J.; Arroyave-Franco, M.; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)Rhenium diboride (ReB2) in its P6(3)/mmc crystalline structure, is widely known as a super-hard material, and has been studied many times using the Density Functional Theory (DFT) approach. In this work the same chemical composition was studied in three additional unreported hypothetical crystallographic phases by means of DFT with the hybrid functional approach, and the elastic constants of each phase were calculated. The elastic behavior of ReB2 was analyzed by means of elastic moduli calculations. Additionally, the velocities of the elastic waves of each phase were calculated, along with the Debye's temperatures, also elastic anisotropy is studied. Semi-empirical and empirical models of hardness were used to estimate qualitatively which phases are or are not hard. It has been determined that the elastic moduli of two out of the three hypothetical phases are desirable and the elastic waves move very slow (< 2 km/s) in one of them. These results and the analysis of the bond critical points (bcp) of each phase allow us to conclude that one of them is soft while the other two are hard. The synthesized phase of ReB(2)P6(3)/mmc was studied in order to compare and confirm the results. (C) 2016 Elsevier B.V. All rights reserved.Ítem Mechanical properties study for new hypothetical crystalline phases of ReB2: A computational approach using density functional theory(Elsevier, 2016-09-01) Marín-Suárez, M.; Vélez, M.E.; David, J.; Arroyave-Franco, M.; Marín-Suárez, M.; Vélez, M.E.; David, J.; Arroyave-Franco, M.; Universidad EAFIT. Departamento de Ciencias; Lógica y ComputaciónRhenium diboride (ReB2) in its P6(3)/mmc crystalline structure, is widely known as a super-hard material, and has been studied many times using the Density Functional Theory (DFT) approach. In this work the same chemical composition was studied in three additional unreported hypothetical crystallographic phases by means of DFT with the hybrid functional approach, and the elastic constants of each phase were calculated. The elastic behavior of ReB2 was analyzed by means of elastic moduli calculations. Additionally, the velocities of the elastic waves of each phase were calculated, along with the Debye's temperatures, also elastic anisotropy is studied. Semi-empirical and empirical models of hardness were used to estimate qualitatively which phases are or are not hard. It has been determined that the elastic moduli of two out of the three hypothetical phases are desirable and the elastic waves move very slow (< 2 km/s) in one of them. These results and the analysis of the bond critical points (bcp) of each phase allow us to conclude that one of them is soft while the other two are hard. The synthesized phase of ReB(2)P6(3)/mmc was studied in order to compare and confirm the results. (C) 2016 Elsevier B.V. All rights reserved.Ítem Síntesis y caracterización de películas delgadas de Reb2 en Co-deposición con Ti mediante la técnica Magentrón Sputtering(Universidad EAFIT, 2023) Ruiz Daza, Carolina Rocío; Arroyave Franco, Mauricio; Palacio Espinosa, Claudia ConstanzaUsing the reactive magnetron sputtering technique, Rhenium Boride films in co-deposition with Titanium were grown on steel substrates at 100°C. To improve the adhesion of the coating a stack of twelve Ti/TiN bilayers was grown using a reactive atmosphere of argon and nitrogen with a ratio Ar/N2=40/1.4 sccm meanwhile, radio frequency power, negative bias voltage, working pressure, and temperature of 100°C were fixed in the experiments to produce the (ReB2):Ti. A design of experiments with a fraction-factorial style was made with four inputs and two outputs with 3 different levels. A matrix of procedures was defined for a total of 9 experiments. The titanium target was powered with 30 and 60 watts during the co-deposition with ReB2 to evaluate the content of titanium at different ratios. Structural and compositional measurements were carried out using SEM, XRD, and XPS to confirm the formation of (ReB2):Ti and AFM analysis to measure the thickness and observe the morphology of samples. Furthermore, mechanical properties were measured with nano hardness equipment, showing that the addition of titanium to ReB2 coating has a significant improvement on the chemical stability of ReB2 on steel and preserves mechanical properties of hardness and high Young’s module, which makes the material suitable for applications in the mechanical industry reaching hardness around 20 GPa.Ítem Time dependent deformation behavior of dentin(PERGAMON-ELSEVIER SCIENCE LTD, 2017-04-01) Montoya C; Arola D; Ossa EA; Montoya C; Arola D; Ossa EA; Universidad EAFIT. Departamento de Ingeniería de Producción; Materiales de IngenieríaObjective The viscoelastic behavior of dentin and its ability to undergo time dependent deformation are considered to be important to oral functions and its capacity to resist fracture. There are spatial variations in the microstructure of dentin within the crown, which could be important to the viscous behavior. However, a spatially resolved description for the viscoelastic behavior of coronal dentin has not been reported. Methods In this investigation spherical indentations were made in three regions of coronal dentin including the outer, middle and inner regions. Power law relations were developed to quantitatively describe the stress-strain responses of the tissue. Results Results showed that the deformation behavior was strongly dependent on the composition (mineral to collagen ratio) and microstructure (tubule density), which contributed to an increase in the rate of viscous deformation with increasing proximity to the pulp. Conclusions A model accounting for spatial variations in composition and microstructure was developed to describe the steady-state time dependent deformation behavior of coronal dentin, and a good agreement was found with the experimental results. © 2017 Elsevier Ltd