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  • 1
    Electronic Resource
    Electronic Resource
    Dimensional fit of cast titanium restorations (1993)
    Springer
    Journal of materials science 4 (1993), S. 210-212 
    Details
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Undersizing of cast Ti crowns has been reported to be a problem. The diameter of standardized, cylindrical crowns was studied in this investigation using a photographic technique and cold moulds. The results show that the dimensional problem can be avoided by selecting a standard phosphate-bonded investment with a sufficiently high thermal expansion coefficient. Appropriate casting conditions with a good vacuum (13.3 Pa) gives only a thin (〈10 μm) oxide film and reproducible dimensions of the castings. A ZrO2 coating eliminates or reduces the oxide film and follows the movements of the investment. The diameter of the crown can largely be accounted for by the measured expansion of the investment and thermal contraction of the Ti casting.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00120394
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  • 2
    Electronic Resource
    Electronic Resource
    Porosity and mould filling of titanium castings (1993)
    Springer
    Journal of materials science 4 (1993), S. 296-299 
    Details
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: A vacuum/Ar pressure casting machine was used to study porosity and mould filling of cast bridges of Ti. Two series of experiments were carried out: (1) The melting and the mould chamber were separated by a thin Ti foil until penetrated by the Ti melt. The mould chamber including the mould cavity was evacuated. (2) No separating Ti foil was applied. The pressure in the mould chamber was then controlled by diffusion of Ar through the investment. The moulds were made of two investments with different gas permeability. A standardized wax pattern for a five-unit bridge was used. Mould filling was evaluated by visual inspection and by measuring the missing lengths of the margins of the crowns. The porosity was studied by x-ray radiography and density measurements. In the first series mould filling was satisfactory in all cases, while the porosity was substantial for high Ar pressures. Without a Ti foil (second series) all castings contained little porosity, but the mould filling was adequate only for the high permeability investment. The experiments show that porosity can be avoided by maintaining small pressure differences between the melting chamber and the mould cavity. Adequate mould filling is promoted by minimal back pressures from trapped Ar gas in the mould.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00122284
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  • 3
    Electronic Resource
    Electronic Resource
    On the bonding of porcelain on titanium (1992)
    Springer
    Journal of materials science 3 (1992), S. 186-191 
    Details
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The interface structure and bond strength between Ti and porcelain were studied using various firing times and vacuum levels. During firing an interfacial oxide layer was formed between Ti and porcelain. Fracture occurred between this oxide layer and Ti. A correlation was observed between the thickness of the interfacial layer and the bond strength: the thicker the layer, the weaker was bonding. An improved vacuum was found to increase the bond strength. Oxygen was observed by ESCA to dissolve into Ti, causing brittleness in the uppermost Ti layer with prolonged firing time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00713448
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  • 4
    Electronic Resource
    Electronic Resource
    Bioactive double glass coatings for Co-Cr-Mo alloy (1995)
    Springer
    Journal of materials science 6 (1995), S. 242-247 
    Details
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Glass compositions for double coatings for a Co-Cr-Mo alloy were developed. The glass compositions were chosen to fulfil such requirements as matching thermal expansion, low glass transition temperature and moderate solubility. For the ground coat a fairly high durability is required, whereas the cover coat must be bioactive, i.e. become attached to living bone by a chemical bond. Two compositions of each type were developed by computer-aided optimization. The glasses were chosen in the Na2O−CaO−B2O3−Al2O3−SiO2−P2O5 system. The bioactivity was tested in vitro by immersion in a simulated body fluid. The double coatings on Co−Cr−Mo alloy released hexavalent chromium into the solution as detected by yellow colouration and spectrophotometry. This colouration was strong at the margin between coated and uncoated metal and may be explained by oxidation of trivalent chromium of the alloy in the presence of glass. The released chromium did not have any notable effect on the calcium phosphate formation. After replensihing the solution no coloration was observed. This suggests that the chromate is easily dissolved and that it may be possible to wash it out prior to implantation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00146863
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  • 5
    Electronic Resource
    Electronic Resource
    Corrosion of gallium alloys in vivo (1997)
    Springer
    Journal of materials science 8 (1997), S. 357-360 
    Details
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The aim of this work was to study the corrosion of gallium alloys in vivo. Three gallium alloys were tested: GF alloy, Galloy and an experimental GaIn alloy. An amalgam was applied as a control. After ageing for a minimum of two weeks, one disc of each of these alloys was mounted with the polished side up in the buccal surfaces of 17 acrylic dentures. Eight sets of the specimens were retrieved after exposure to the oral cavity for 2–4 months, and another seven were retrieved after 6–9 months. Corrosion of the polished cross-sections of the specimens was studied using scanning electron microscopy (SEM). Only the CuGa2 phase was found to corrode substantially in all three of the alloys investigated, leaving behind holes up to 20 μm deep. This is consistent with the corrosion reported after immersion tests in a solution of 0.1 mol lactic acid and 0.1 mol NaCl for 7 days. Such in vitro tests are also reported to cause distinct corrosion of the Sn phase in the gallium alloys. However, a salient feature of the corrosion in vivo was the lack of detectable dissolution of this phase. Thus, for gallium alloys, the accelerated in vitro immersion method produced results which did not agree with clinical observations. Large variations in the corrosion of the CuGa2 were observed from patient to patient. The amount of corrosion on the Galloy specimens appeared to be less and on a finer scale than on specimens of the two other alloys. The depth of corrosion was thus shallower than for this alloy. This finding indicates that there is room for further improvement of the corrosion resistance by modifying the microstructures. Less overall corrosion was found for the amalgam control than for the gallium alloys.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018528832317
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  • 6
    Electronic Resource
    Electronic Resource
    The mould-filling capacity of two casting alloys (1990)
    Springer
    Journal of materials science 1 (1990), S. 94-99 
    Details
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The mould-filling capacities of an Au-Ag-Cu alloy and a Ni-Cr-Be alloy for dental use have been studied by measuring the lengths of cast helices of a constant cross-section as a function of the supertemperature of the melt. A vacuum-pressure casting machine was applied in the experiments. Assuming that the conduction of heat through the investment is rate-controlling for the heat flow, the heat of fusion was calculated for the two alloys. These values were found to be close to those obtained by differential thermal analysis measurements. The lengths of the helices are strongly influenced by the deliberated heat of fusion during solidification. The substantially higher mould-filling capacity of the Ni-Cr-Be alloy compared with that of the Au-Ag-Cu alloy can be explained to a large extent by the corresponding difference in their latent heat of fusion. A calculation of the lengths of the helices requires a knowledge of the speeds of the melts. So far there are only indications of a higher speed for the Ni-Cr-Be alloy than for the Au-Ag-Cu alloy with the casting machine employed. The highest slope for the length of helix against supertemperature curve was observed for the Au-Ag-Cu alloy, indicating a smaller heat transfer coefficient for this alloy than for the Ni-Cr-Be alloy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00839074
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  • 7
    Electronic Resource
    Electronic Resource
    Transmission electron microscopy study of a dental gallium alloy (1996)
    Springer
    Journal of materials science 7 (1996), S. 447-455 
    Details
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Analytical transmission electron microscopy (TEM) studies of a dental gallium alloy have been carried out. This commercial Ga alloy was made by triturating a Ag-Sn-Cu-rich alloy powder with a liquid Ga alloy containing Ga, In and Sn. Ga alloys are of increasing interest as an alternative to amalgam. The dental material studied in the present work was found to be a composite consisting of remaining, undissolved particles from the Ag-based alloy powder in a matrix of reaction products with the liquid Ga alloy. The phases in the matrix and the remaining Ag-based alloy particles have been identified by electron diffraction, high resolution electron microscopy and energy dispersive X-ray spectroscopy. the following phases were identified: orthorhombic Ag3Sn, cubic γ-Cu9Ga4, cubic Ag9In4, tetragonal β-Sn and hexagonal Ag2Ga. In addition to these well-known phases Ga-rich regions of Cu-Ga were observed consisting of an intergrowth of the tetragonal CuGa2 and one of the cubic γ-Cu9Ga4 phases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00122015
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  • 8
    Electronic Resource
    Electronic Resource
    Effect of palladium on sulfide tarnishing of noble metal alloys (1985)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 19 (1985), S. 917-934 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Electron spectroscopic studies of Au—Ag—Cu alloys of the type used for dental castings show that small additions (≤3 wt%) of palladium reduce essentially the thickness of the sulfide layer formed on surfaces of samples treated in aqueous Na2S solutions. Relative to silver, palladium does not enrich in the sulfide, but statistically significant enrichment is found immediately below the sulfide layer. This enrichment probably takes place during the exposure of the substrate surface to atmosphere before the sulfiding treatment. The mechanism of the impeding effect of palladium on sulfiding is assumed to be a decrease in diffusion from the bulk alloy to the surface due to the enriched layer. The effect cannot be explained by changes in the electronic structure of the alloy due to palladium alloying.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jbm.820190804
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  • 9
    Electronic Resource
    Electronic Resource
    Bonding capacity in bone of HIP-processed HA-coated titanium: Mechanical and histological investigations (1995)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 29 (1995), S. 1443-1449 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The main problems using plasma-sprayed hydroxyapatite (HA) as a coating material on metallic implants are its porosity, low fatigue strength, and weak adherence to the metallic substrate. To overcome these problems a new technique using hot isostatic pressing (HIP) has been developed for producing HA-coated titanium (Ti) implants. Specimens produced at a maximum temperature of 850°C and a maximum pressure of 720 bar displayed a dense, glassy, 25-μm thick coating with small amounts of porosity and a mean surface roughness of 0.7μm, as compared with 1.6 μm for sandblasted Ti. Twenty conical HA-coated (720 and 100 bar pressure) and 10 noncoated Ti implants were inserted through the cortex of the lower margin of the mandibles of sheep and allowed to heal for 60 days. Push-out tests for implants processed at 720 bar pressure showed substantially higher bone/implant bonding values than for sandblasted Ti implants. Histological studies indicated a direct contact and probably chemical bonding between bone tissue and the HA coatings. The area of contact was almost 3 times as large as for the Ti implants. The adherence of the 100-bar coating to the Ti surface was inferior to the 720-bar coating, as shown by the loosening of the coatings in several areas. © 1995 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jbm.820291116
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