Abstract: A radio opaque denture base formed of a copolymer of an ethylenically unsaturated monomer containing chemically bound tin together with at least one ethylenically unsaturated monomer, the ethylenically unsaturated monomer containing chemically bound tin being an ester of trialkyl tin and an ethylenically unsaturated acid such as tributyl tin ethacrylate. In a preferred embodiment the copolymer is a novel copolymer derived from two ethylenically unsaturated tin containing monomers one of which is trimethyl tin methacrylate and the other is a trialkyl tin methacrylate other than trimethyl tin methacrylate. In another preferred embodiment the copolymer is a novel copolymer derived from an ester of trialkyl tin and an ethylenically unsaturated carboxylic acid together with two or more other ethylenically unsaturated monomers, one of which is a long chain alkyl acrylate or methacrylate and another of which is a lower alkyl acrylate or methacrylate.