BOSTON, May 5.—P— It was so cold at times during the government’s expedition to Antarctica that “the fillings dropped out of our teeth,” members of the exploring par ty said today on their return. » Temperatures ranging down to 72.6 degrees below zero—the lowest ever recorded at Little America—contracted the fill ings, the men asserted, and re sulted in a new adventure in primitive dentistry. Dr. Paul A. Siple, one of the scientists, said a technique was devised whereby a form of un breakable glass was mixed with a chemical and used as a sub stitute for regular fillings.