[The manufacturer] used thorium and rare-earth elements in making industrial products including mantles for gas lanterns; the toothpaste was produced as a byproduct.

I think “Ausgiebig im Gebrauch” means the opposite of “use extensively”

The WWII section:

During the German military administration in occupied France during World War II, a group of German scientists stole all the thorium they could while in occupied France. The Allied Alsos Mission thought they were using the heavy elements for the refinement of uranium to be used in an atomic bomb. However, after Allied agents captured and investigated a German chemical company’s representative, it was revealed that the scientists were not seeking to develop an atomic bomb at all, but to make thorium toothpaste.