Disclosed are casting resins made from acrylic acid esters with a high content of finely dispersed fillers. The casting resins contain a polymeric organosilicon compound having functional and nonfunctional groups. As functional groups, the copolymer contains one or more alkoxysilyl groups and one or more (meth)acryloxysilyl groups. The copolymer furthermore contains by copolymerization at least one nonfunctional comonomer having an ethylenically unsaturated grouping as well as an additional comonomer of the group of the vinyl carboxylic acid esters and (meth)acrylic acid esters, if desired. The addition of these polymeric organosilanes to known casting resins brings about a greater lowering of the viscosity of these resins, which are used, for example, for the manufacture of sanitary appliances.