摘要:

AbstractElectron diffraction evidence confirming the ordered orthorhombic crystal structure of the γ phase of the silver–tin system has been obtained, and it has been established by optical metallography that an alloy with a composition corresponding to the dental amalgam alloy formula Ag3Sn (i.e., 26.85 wt % Sn) lies outside the single γ phase field and in the duplex (γ + Sn) phase field adjacent to it. Studies of the mechanism of the hardening reaction of single crystals of homogeneous γ phase alloys with mercury were carried out using both scanning and transmission electron microscopy. Mercury attack occurred preferentially along welldefined planes in the single crystals. Using electron channeling and trace analysis techniques these planes of preferential attack were found to be {010} and {011}, and from transmission electron microscopy of thin foils these were shown to be slip bands and deformation twins, respectively. In bicrystals of γ phase material, preferential attack also occurred along grain boundaries. Similar preferential mercury attack, leading to the development of deep planar intrusions into the γ phase material, was observed in an experimental dental amalgam prepared from a lathe‐cut homogeneous γ phase amalgam alloy. It is believed that the presence of such features would have important implications for the clinical performance of dent

ISSN:0021-9304    

DOI:10.1002/jbm.820160502

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractThe matrix of a stoichiometric zinc polycarboxylate cement has been shown to be identical with zinc polycarboxylate salt, which consists principally of neutralized carboxylate groups with a few free acid groups. When excess zinc oxide is present, as in practical cements, there are no free acid groups present. There is no evidence for the formation of a chelate. Both salt and cement matrices are amorphous. The formation of the salt appears to control timedependent changes in the consistency of the cement pastes.

ISSN:0021-9304    

DOI:10.1002/jbm.820160503

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractTo assess abrasive wear of mechanical valve prostheses containing pyrolytic carbon components, we recovered at necropsy or surgery and analyzed by scanning electron microscopy and surface profilometry eight prostheses. Seven were implanted for 30–85 (mean 50 months). Valves included DeBakey aortic (2), DeBakey mitral (1), Beall mitral (2), Bjork–Shiley aortic (1), Cooley–Cutter mitral (1), and Lillehei–Kaster (L–K) tricuspid (1). All carbon occluders had undetectable wear. Carbon cage struts had a superficial burnish. Metallic struts had insignificant wear marks. In contrast, a Teflon Beall Model 104 valve implanted for 34 days and similarly analyzed had considerable material loss from the cage struts. This study suggests that clinically important abrasive wear will not be a late complication of cardiac valve replacement with pyrolytic carbon p

ISSN:0021-9304    

DOI:10.1002/jbm.820160504

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractTwenty‐four rectangular metal plates were fabricated with surface regions in three different pore size ranges (5–20 μm, 20–50 μm, 50–200 μm). The plates were implanted into the dorsal subcutaneous tissue of 12 adult mongrel dogs for periods of 4, 8, 12, and 16 weeks. After animal sacrifice, the fibrous tissue which adhered to the porous‐surfaced regions of each plate was mechanically peeled off to give an indication of the strength of tissue attachment. The tissue was examined by both transmitted light and scanning electron microscopy. At each time period, the tissue that contacted the porous regions was found to be collagenized fibroconnective tissue. The mechanical tests indicated an increasing strength of tissue attachment with increasing implantation time and pore size range. The largest pore size range of approximately 50–200 μm produced a mean peel strength of attachment of 27.5 g/mm at the

ISSN:0021-9304    

DOI:10.1002/jbm.820160505

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractThe particle size and adsorbed water on zinc oxide from various sources have been investigated and related to the reactivity with eugenol. The reactivity of zinc oxide with eugenol alone increases with the amount of water reversibly adsorbed. When 1% acetic acid is added to eugenol, the reactivity increases as the particle size of the oxide decreases. Generally, zinc oxide powders are deactivated by heat treatment because of coalescence of particles and loss of the ability to readsorb water.

ISSN:0021-9304    

DOI:10.1002/jbm.820160506

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractThe continuous compressive creep curves of four distinct types of one‐week‐old dental amalgam were monitored for one day on a specially designed mini‐specimen creep apparatus. Creep conditions included three different applied constant stress levels (20, 40, and 80 MPa), and temperatures ranging from 0°C to 60°C. To compensate for changing dimensions at high creep strains, the data was converted to terms of compressive creep compliance. For all types of dental amalgam, compressive creep increased both with increased applied stress and with increased test temperature. The two high copper systems evaluated appear to approach a steady‐state creep condition up to the highest temperatures tested, but the two conventional amalgams appear to change their creep exponent precipitously at temperatures a

ISSN:0021-9304    

DOI:10.1002/jbm.820160507

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractPoly(hydroxyethyl methacrylate) (PHEMA) was implanted subcutaneously in rats, hamsters, and guinea pigs for up to 24, 23, and 13 months, respectively. The tissue response and tumorigenesis caused by PHEMA were compared among the three species of the animals. Thick fibrous capsule formation and tumor production were noted only in rats, while no tumorigenesis and thin fibrous capsule formation were observed in hamsters and guinea pigs.These results support our previous hypothesis that animals producing a thick and avascular capsule tend to develop tumors at the implant site. PHEMA retrieved was characterized by scanning electron microscopy and x‐ray energy dispersive analysis. Calcium and phosphorus were the main elements detected on the surface of PHEMA implants. PHEMA is suggested to be not suitable for long‐term implant mater

ISSN:0021-9304    

DOI:10.1002/jbm.820160508

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractComposite materials were made by sedimention of ceramic powders in methyl methacrylate which was then polymerized by γ‐irradiation. Inclusion of 4‐methacryloxyethyl trimellitic anhydride (4‐META) generally was found to result in an increase in Knoop hardness number, Young's modulus, and transverse strength. Most emphasis was placed on transverse strength which was found to be increased by ca. 30% by inclusion of 4‐META (5 wt %) in composites made with silanated LiAlSiO4.However an abrupt decrease in strength was found for composites with greater than ca. 83 wt % silanated LiAlSiO4. This was shown by fractography to be due to increased porosity and dewetting at the higher filler contents. Fractography also indicated that inclusion of 4‐META results in a more coherent polymeric matrix. Further evidence for greater coherence was obtained by showing that 4‐META confers resistance to disintegration b

ISSN:0021-9304    

DOI:10.1002/jbm.820160509

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractOwing to the chemical instability of prostacyclin, the direct immobilization of thsi prostaglandin has not been successful. A new procedure is described for the preparation of immobilized prostacyclin based on the conversion of immobilized prostaglandin F2αto immobilized prostaglandin I2. Materials thus prepared show dramatic antiplatelet effects with regard to platelet aggregation and platelet adhesion. Radioimmunoassays of plasmas used inin vitroplatelet tests and of buffers used in prostacyclin leakage studies established that these effects are not due to the release of prostacyclin from the respective immobilization substrates

ISSN:0021-9304    

DOI:10.1002/jbm.820160510

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY

摘要:

AbstractThe effect of varying the initial temperature of the components of poly(methyl methacrylate) (PMMA) bone cement has been investigated. Electron paramagnetic resonance (EPR) spectroscopy was used to monitor free radical decay during the curing of the cement. Samples cured in saline at 37°C were found to exhibit first‐order decay kinetics for the polymerization radicals for approximately one week after mixing. This indicates that the decay did not take place by combination or disproportionation and was probably due to a transfer process. Decreasing the temperature of the bone cement components prior to mixing resulted in smaller decay rates, but still with first‐order kinetics. This decrease in decay rate with lower initial temperature may be due to decreased porosity of the cement, possibly due to decreased monomer evaporation. SEM micrographs of the samples were consistent with this change in poro

ISSN:0021-9304    

DOI:10.1002/jbm.820160511

出版商:John Wiley&Sons, Inc.    

年代:1982

数据来源: WILEY