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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 1921-1923 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A technique was developed to determine the spatial localization of radio-opaque resonant markers in newly formed bone by synchrotron x-ray microtomography. The resolution of the technique shows potential for three-dimensional tomographic mapping of bone mineral deposition, as an index of bone formation. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    PO Box 1354, 9600 Garsington Road, Oxford OX4 2XG, UK. : Blackwell Science Ltd
    Fatigue & fracture of engineering materials & structures 28 (2005), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The fracture of bone is a health concern of increasing significance as the population ages. It is therefore of importance to understand the mechanics and mechanisms of how bone fails, both from a perspective of outright (catastrophic) fracture and from delayed/time-dependent (subcritical) cracking. To address this need, there have been many in vitro studies to date that have attempted to evaluate the relevant fracture and fatigue properties of human cortical bone; despite these efforts, however, a complete understanding of the mechanistic aspects of bone failure, which spans macroscopic to nanoscale dimensions, is still lacking. This paper seeks to provide an overview of the current state of knowledge of the fracture and fatigue of cortical bone, and to address these issues, whenever possible, in the context of the hierarchical structure of bone. One objective is thus to provide a mechanistic interpretation of how cortical bone fails. A second objective is to develop a framework by which fracture and fatigue results in bone can be presented. While most studies on bone fracture have relied on linear-elastic fracture mechanics to determine a single-value fracture toughness (e.g., Kc or Gc), more recently, it has become apparent that, as with many composites or toughened ceramics, the toughness of bone is best described in terms of a resistance-curve (R-curve), where the toughness is evaluated with increasing crack extension. Through the use of the R-curve, the intrinsic and extrinsic factors affecting its toughness are separately addressed, where ‘intrinsic’ refers to the damage processes that are associated with crack growth ahead of the tip, and ‘extrinsic’ refers to the shielding mechanisms that primarily act in the crack wake. Furthermore, fatigue failure in bone is presented from both a classical fatigue life (S/N) and fatigue-crack propagation (da/dN) perspective, the latter providing for an easier interpretation of fatigue micromechanisms. Finally, factors, such as age, species, orientation, and location, are discussed in terms of their effect on fracture and fatigue behaviour and the associated mechanisms of bone failure.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1433-2965
    Keywords: Key words:Micro-CT – Osteoporosis – Plain radiograph – Three-dimensional – Trabecular bone – Trabecular architecture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract: The purpose of this study was to determine the relationship between three-dimensional (3D) trabecular structure and two-dimensional plain radiographic patterns. An in vitro cylinder of human calcaneal trabecular bone was three-dimensionally imaged by micro-CT using synchrotron radiation, at 33.4 μm resolution. The original 3D image was processed using 14 distinct sequences of morphologic operations, i.e., of dilations and erosions, to obtain a total of 15 3D models or images of calcaneal trabecular bone. These 15 models had distinct densities (volume fractions) and architectures. The 3D structure of each calcaneal model was assessed using mean intercept length (fabric), by averaging individual fabric measurements associated with each medial-lateral image slice, and determining the relative anisotropy, R3D, of the structure. A summated pattern or plain radiograph was also computed from the 3D image data for each calcaneal model. Each summated pattern was then locally thresholded, and the resulting two-dimensional (2D) binary image analyzed using the same fabric analysis as used for the 3D data. The anisotropy of the 2D summated pattern was denoted by Rx-ray. The volume fractions of the 15 models ranged from 0.08 to 0.19 with a mean of 0.14. The medial-lateral anisotropies, R3D, ranged from 1.38 to 2.54 with a mean of 1.88. The anisotropy of the 2D summated patterns, Rx-ray, ranged from 1.35 to 2.18 with a mean of 1.71. The linear correlation of the 3D trabecular architecture, R3D, with the radiographic trabecular architecture, Rx-ray, was 0.99 (p〈0.0001). This study shows that the plain radiograph contains architectural information directly related to the underlying 3D structure. A well-controlled sequential reproducible plain radiograph may prove useful for monitoring changes in trabecular architecture in vivo and in identifying those individuals at increased risk of osteoporotic fracture.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0021-9304
    Keywords: dentin ; demineralization ; shrinkage ; rehydration ; atomic force microscopy ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Most current dentin bonding procedures use acid etchants to partially demineralize the dentin structure and provide pathways for resin infiltration. This study determined the recession rates of peritubular dentin and intertubular dentin as a function of pH during demineralization in citric acid solutions (0.0005-2.5M) and the effects of dehydration and rehydration on the partially demineralized dentin. Polished dentin disks were prepared with an internal reference layer and were studied at specific intervals for citric acid etching between pH 1 and 3.4 in an atomic force microscope. Peritubular dentin etched rapidly and linearly with time until it could no longer be measured. The intertubular surface began etching at nearly the same rate, but then recession slowed for all concentrations and stabilized after recession of less than 1 μm for all but the pH 1 solution. The decrease in recession was attributed to the limitation of contraction of the demineralized collagen scaffold as long as it remained hydrated. Dehydration following etching resulted in significant collapse of the surface, changes in roughness, and a slight decrease in tubule diameter for samples etched for 30 min. Measurements could not be made of the collapse for low pH samples, because shrinkage stresses disrupted the integrity of the reference layer. On rehydration, the dehydrated surfaces underwent an expansion up to the level seen after etching and tubule diameters returned to the etched values. These results indicate that the collapse of demineralized matrix is almost totally recoverable on rehydration. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 42, 500-507, 1998.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 29 (1995), S. 1381-1387 
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Dentin conditioners provide a microporous surface for penetration by bonding agents. This study used an atomic force microscope (AFM) to examine the initial steps in the conditioning process of dentin using three demineralizing agents, 0.5 M EDTA, and dilute solutions of phosphoric (3mM, 6mM) and citric (5 mM) acids, in order to establish the relationships between demineralization and changes in surface morphology. Polished dentin disks had a 10-nm-thick gold pattern applied which served as a height reference. Samples(n = 3/agent) were examined at baseline and at 2-s intervals for up to 120 s for each agent. EDTA (0.5 M) was used as received; other conditioners were diluted to slow the rates of demineralization for detailed study. The surfaces of the peritubular and intertubular regions were altered differently. Initially subsidence rates were equal and linear, but after a 100-nm depth change the intertubular rates decreased. For phosphoric acid and citric acid, the movement of the intertubular surface was uniform and the surfaces remained smooth. However, the intertubular surfaces were rough for the EDTA treatment. The surface subsidence reached a plateau after a depth change of about 0.5μm, which resulted from a limit to the contraction of the demineralized and hydrated collagen scaffold. © 1995 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0021-9304
    Keywords: atomic force microscope (AFM) ; dentin ; collagen ; viscoelasticity ; mechanical properties ; elastic modulus ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Using an atomic force microscope (AFM) with an attachment specifically designed for indentation, we measured the mechanical properties of demineralized human dentin under three conditions: in water, in air after desiccation, and in water after rehydration. The static elastic modulus (Ehr = 134 kPa) and viscoelastic responses (τε = 5.1 s and τσ = 6.6 s) of the hydrated, demineralized collagen scaffolding were determined from the standard linear solid model of viscoelasticity. No significant variation of these properties was observed with location. On desiccation, the samples showed considerably larger elastic moduli (2 GPa), and a hardness value of 0.2 GPa was measured. Upon rehydration the elastic modulus decreased but did not fully recover to the value prior to dehydration (381 kPa). © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 539-544, 1998.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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