During the late 1950s and early 1960s, as debate raged over the dangers of nuclear weapons testing, volunteers in St. Louis collected hundreds of thousands of baby teeth in an attempt to discover the impact of radioactive nuclear fallout on human health.  Although that question never received the kind of scientific scrutiny necessary to provide a definitive answer, a major study now underway at Harvard University, based on the long-forgotten teeth, should finally produce conclusive results.