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OwnerJurgen Engelbrecht, Michael Gunther +1inventors
InventorsJurgen Engelbrecht, Michael Gunther, Helmut von Wallis
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Silica gels of a mean grain size of about 0.5 to 50 .mu.m are subjected to a heat or acid treatment that considerably reduces their surface area and the volume of pores smaller than 50 nm, while maintaining approximately the same grain size distribution and amorphous structure. These products are colorless and can be worked into a resinous molding material in relatively large quantities, especially as a filler for dental materials based on polymerizable monomers, in particular mono-, di- or polyfunctional esters of acrylic or methacrylic acid. In the completely hardened condition, these materials have good mechanical characteristics, less polymerization shrinkage, very low thermal expansion coefficients, excellent transparency and tooth similarity resulting from the favorable refractive index of the filler, as well as very good ability to be polished and abrasion resistance.
A filler for dental materials comprising a surface area-reduced silica gel, which has been prepared by roasting a silica gel of a mean grain size of about 0.5 to 50 .mu.m at a temperature of between 500.degree. and 1,200 .degree. C. and/or by acid-catalytically treating a silica gel, and which has an essentially unchanged mean grain size of about 0.5 to 50 .mu.m, a BET surface area reduced to not larger than 200 m.sup.2 /g, and a volume of pores smaller than 50 nm reduced to less than 30 percent of the total pore volume.
Dependencies are inferred from the claim text.