Properties of leucite-glass composites prepared by a coprecipitation process
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Stephen T. Rasmussen and William J. O'Brien^ Department of Biologic and Materials Sciences, School of Dentistry, The University of Michigan, 1011 North University, Ann Arbor, Michigan 48109-1078
Tseng-Ying Tien Department of Materials Science Engineering, School of Engineering, The University of Michigan, Ann Arbor, Michigan 48109-2136 (Received 15 June 1992; accepted 2 May 1994)
The purpose of this investigation was to study the effect of changes in composition and thermal history on some properties of potential leucite-glass composites made by a coprecipitation process. Four compositions from the K 2 0 - A l 2 0 3 - S i 0 2 system were investigated for differences in phases, density, thermal expansion, and strength. Strength, density, and thermal expansion increased with increasing leucite content. Strengths of up to 140 MPa were obtained with air-fired specimens. Composites with different thermal expansion coefficients could be obtained by altering SiO2 content in a predictable way. Leucite-glass composites offer potential for improved dental porcelains.
I. INTRODUCTION Ceramic-metal crowns and bridges are aesthetic and the most long lasting of the full coverage restorative materials. All ceramic crowns are generally more aesthetic, but are currently recommended for use as anterior crowns only.1"3 Materials with flexure strengths in the 140—150 MPa range had adequate clinical success rates for all ceramic anterior crowns, but gave unacceptable failure rates (15.2% over seven years) for posterior crowns.3 McLean3 hypothesized that flexure strengths of ceramics for posterior restorations may need to be as high as 500 MPa. The first successful dental porcelain4 for use with a metal substrate had a potash feldspar type composition, leucite-glass structure,5 and strength of 90 MPa.6 Dispersed crystalline phases have been added to the feldspar matrix to strengthen dental porcelains. McLean and Hughes 7 achieved a strength of 131 MPa for their alumina dispersed ceramic (40-50%) as compared to regular porcelain. Morena et al.8 obtained a 30% increase in toughness relative to their feldspar control by the addition of zirconia. However, they noted that the addition of approximately 25 vol. % of zirconia or alumina to achieve a noticeable toughness increase of dental porcelains would adversely affect translucency. A number of different approaches have been taken to produce nontraditional ceramics for use in all ceramic a 'Address
all correspondence to this author. J. Mater. Res., Vol. 9, No. 9, Sep 1994
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crowns: (i) an alumina-spinel dispersion strengthened glass has a strength of 118 MPa,9 (ii) a castable glass which could be crystallized by a heat treatment giving it a strength of 152 MPa,10 and (iii) a magnesia ceramic for use as a core material has a flexure strength of 131 MPa and is compatible with available high expansion feldspar porcelains.2 Little research has been directed at the effect of leucite on the strength of dental porcelains. Morena et al.8 not
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