Dental root canal filling cones are prepared from a filler and a thermoplastic polymer, wherein the thermoplastic polymer is formed by polymerization of polymerizable diepoxide monomer and amine monomer. The amine monomers are primary monoamine and/or a disecondary diamine. The filler has about 40 to 90 weight-% of the cones providing a radio-opacity of at least 3 mm/mm aluminum.