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  • National Institutes of Health (U.S.)  (81)
  • Female  (72)
  • Polymer and Materials Science  (69)
  • 1
    Electronic Resource
    Electronic Resource
    Effects of porcelain application procedures on two noble alloysDegudent U, 77.5%Au, 10Pt. 9Pd. Sn, In, Degussa Dental Inc., Long Island, NY.Based on a Ph.D. thesis by M. Bagby done in the Department of Biological Materials, and submitted to the Graduate School, Northwestern University, Chicago, IL. (1990)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Biomaterials 1 (1990), S. 31-37 
    Details
    ISSN: 1045-4861
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Distortion of ceramometal restorations during porcelain application is often attributed to mismatch of thermal expansion coefficients. Little attention has been paid to treatment the metal receives after casting. Oxide formation, lattice parameter changes, and macroscopic distortion were studied for flat specimens of two ceramometal alloys, a high Pd alloy and a high Au alloy. SnO2 and In2O3 formed on the surface of the high Au alloy after the oxidation firing, while SnO2 and CuGa2O4 formed on the high Pd alloy. Lattice parameter changes reflected the loss of base metal elements in the formation of surface oxides. The edges of specimens distorted toward the ground side. Such distortion can be explained by the induction of residual stress in the metal surface during grinding and subsequent surface stress annealing accompanied with subsurface elastic recovery during firings. Oxide formation was not related to specimen distortion. This study suggests a relationship between surface preparation and specimen distortion during porcelain application procedures.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jab.770010106
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  • 2
    Electronic Resource
    Electronic Resource
    Time-Dependent phase changes in Cu-rich amalgamsBased in part on a paper presented at the Fourth Annual Meeting of the Society for Biomaterials, San Antonio, Texas, May 1978. (1979)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 13 (1979), S. 395-406 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Cu-rich amalgams represent a significant change in amalgam alloy formulation which may result in enhanced performance. Significantly, these systems reduce or eliminate the γ2 phase. This work studied the phase changes which occurred from one hour to six months in 13 commercial amalgams by x-ray diffraction. This included 9 two-particle or blend systems and 4 single-particle systems. γ2 was found in all systems, but was reduced or eliminated on storage at 37°C at rates which varied from system to system. During γ2 elimination, the Cu6Sn5 content correspondingly increased, indicating that solid-state reaction occurs for up to six months in some systems.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jbm.820130305
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  • 3
    Electronic Resource
    Electronic Resource
    Corrosion product formation sequence on Cu-rich amalgams in various solutionsPortions of this work were presented at the 60th General Session of IADR, New Orleans, Louisiana, March 1982. (1983)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 17 (1983), S. 913-920 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: A single particle and four blended Cu-rich amalgam systems were immersed in 37 °C solutions for 1-20 months in order to determine the characterization and sequence of corrosion product formation. X-ray diffraction and SEM/EDS were used to characterize the products. The same sequence of formation occurred in all systems in Ringer's and 0.1% Ringer's solutions. The times at which each product formed varied with the brand of the amalgam and the concentration of the solution. The initial products were ZnSn(OH)6 in Zn-containing systems and SnO2 in most other systems. Cu2O formed next, followed by CuCl2·3Cu(OH)2. Immersion in 1% Na2S yielded only HgS on all brands. A combination of 1% Na2S and Ringer's solution yielded CaSn(OH)6 after 2 months and Cu2O at later periods. Artificial saliva resulted in a retardation of corrosion product formation and only limited amounts of a Sn-rich product could be found after 20 months. Interactions of the various components appear to alter the nature and rate of corrosion product formation on these systems and additional systematic investigations are necessary to understand the influence of these interactions on corrosion.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jbm.820170603
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  • 4
    Electronic Resource
    Electronic Resource
    Cu2O and CuCl2·3Cu(OH)2 corrosion products on copper rich dental amalgamsBased in part on a presentation at the 1980 General Session of the American Association for Dental Research, Los Angeles, CA, March, 1980. (1982)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 16 (1982), S. 81-85 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: In addition to Sn-rich corrosion products found in conventional amalgams, Cu-rich amalgams also form Cu-containing corrosion products. The nature of these Cu-rich products was investigated by immersion of samples of 13 Cu-rich amalgam systems in Ringer's solution for prolonged periods. SEM/EDS and x-ray diffraction studies were used to identify the compounds formed and their morphology. Two products were identified: Cu2O, a red product, and CuCl2·3Cu(OH)2, a green product.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jbm.820160110
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  • 5
    Electronic Resource
    Electronic Resource
    Atomic force microscopy of conditioning agents on dentin (1995)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 29 (1995), S. 1381-1387 
    Details
    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
    URL: http://dx.doi.org/10.1002/jbm.820291109
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  • 6
    Electronic Resource
    Electronic Resource
    Viscoelastic properties of demineralized human dentin measured in water with atomic force microscope (AFM)-based indentation (1998)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 40 (1998), S. 539-544 
    Details
    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.
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  • 7
    Electronic Resource
    Electronic Resource
    Effect of citric acid concentration on dentin demineralization, dehydration, and rehydration: Atomic force microscopy study (1998)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 42 (1998), S. 500-507 
    Details
    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.
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  • 8
    Electronic Resource
    Electronic Resource
    Facilitated synthesis of peptaibols: Alamethicin via enzymatic segment condensation (1992)
    New York : Wiley-Blackwell
    Biopolymers 32 (1992), S. 1461-1470 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have used a combined chemical-enzymatic approach to facilitate the total synthesis of the 20-residue peptaibol, alamethicin. The 1-11 segment of alamethicin, having a C-terminal Gly, and the 12-20 segment, having an N-terminal Leu, were prepared by well-established chemical methods, and then coupled using papain to afford a 54% yield of alamethicin in straightforward fashion. In contrast to the reported chemical syntheses of alamethicin requiring side-chain protection at Glu, 18 the papain-catalyzed coupling proceeded readily and selectively using a C-terminal segment having a free γ-carboxyl group at this position. Several alamethicin partial sequences were obtained via enzymatic formation of the Gly 11-Leu12 bond. The high efficiency of this route is illustrated by the enzymatic assembly of the 1-17 alamethicin fragment on a 400-mg scale in 62% yield. An alternative route to alamethicin through enzymatic formation of the Ala6-Gln7 bond was less successful because of a low yield in the final coupling. © 1992 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360321106
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  • 9
    Electronic Resource
    Electronic Resource
    Conformational analysis and helical preferences of normal and α,α-dialkyl amino acids (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 533-546 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Energy calculations have been performed on right-handed helical structures of L-alanine and α-methylalanine oligomers. A new ′3.610′-helix is described for α-methylalanine peptides. The dependence of the relative stability of the α, 310, and 3.610 structural forms on helix length, dielectric, and force-field, in the gas phase, has been studied. Potential energy surfaces for the interconversion of helices have been generated. The 310-helix in α-methylalanine oligomers exhibits a degree of enthalpic and entropic stabilization not observed for alanine. The relevance of the results to the formation of voltage-sensitive ion channels is discussed.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360300506
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  • 10
    Electronic Resource
    Electronic Resource
    Structural investigation of helices II, III, and IV of B. megaterium 5S ribosomal RNA by molecular dynamics calculations (1992)
    New York : Wiley-Blackwell
    Biopolymers 32 (1992), S. 1263-1270 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structures of the helices II-III region and the helix IV region of B. megaterium 5S rRNA have been examined by means of energy minimization and molecular dynamics calculations. Calculated distances between neighboring hydrogen-bonded imino protons in helices II, III, and IV were between 3.5 and 4.5 Å. The overall axis for the helices II-III region is warped rather than straight. Formation of additional Watson-Crick base pairs in loop B and loop C was not evident from the atomic positions calculated by molecular dynamics. Bases in loop C are well stacked, showing no significant change during dynamics. Bulge migration in helix III does not seem to be possible; the helices II-III region prefers one conformation. Helix II is more stable than helix III. Five base pairs in helix IV were sufficiently stable to establish that helix IV is terminated by a hairpin loop of three nucleotides. U87 protrudes from loop D. Structures of the helices II-III segment and the helix IV segment of B. megaterium 5S rRNA obtained by molecular dynamics were generally consistent with the solution structure inferred from high-field proton nmr spectroscopy. © 1992 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360320915
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