A hardenable medical composition (preferably, dental composition) that includes an ionic redox polymerization system and at least one secondary ionic salt that includes a cation selected from the group consisting of a Group I ion, a Group II ion, an ammonium ion of the formula NR<;SUB>;4<;/SUB>;<;SUP>;+<;/SUP>; wherein each R is H or a (C1-C4)alkyl group, and mixtures thereof.