It's trivial to find sources for the effectiveness of fluoride in preventing tooth decay (Google -> Wikipedia -> a citation leads you here: http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5014a1.htm). There are also studies on water fluoridation's impacts, though it's harder to test that, by nature.
You have only to look up the rates of tooth decay among non-fluoridated countries to find that there is no difference whatsoever.