See the 1997 National Science Council report on recommended intakes of vitamins and minerals

Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride

Starting at page 288, the report discusses various minerals, including fluoride, and presents fluoride as a needed nutrient, just like calcium and magnesium.

This is the same NSC which issued the 2006 NRC Report on Fluoride, the one which is so revealing about the harms which fluorides cause. Like the EPA and FDA, the NSC is a house divided against itself on various issues.