There are provided formable compositions which comprise:(A) 25 to 80% by weight of a glass ionomer cement, containing (a) an aluminum fluorosilicate glass, (b) at least one polymeric polyacid with an average molecular weight >500, (c) water and (d) optionally a chelating agent;(B) and 20 to 75% by weight of a fluoride and/or oxide and/or mixed fluoride and/or mixed oxide of heavy metal elements which are essentially insoluble at ambient temperatures in an aqueous solution containing the polymeric polyacid and/or an aqueous solution containing the chelating agent.The compositions are especially well suited as filling materials for dental root canals.