I worked for Iodent briefly in 1964 at their HQ in downtown Detroit. I was given a tube of Iodent no. 3 and Iodent no. 4 - both tubes releasing "free iodine" while you brush. Manufacture of #'s 3 and 4 ceased in 1930 but no. 3 was in a yellow tube and no. 4 was in a green tube.