Overfluoridation is possible

... - eating canned tuna (including its mercury), over-enthusiastically applying sunscreen (and depriving ourselves of Vitamin D in the process) - we've now reached the point where many Americans, especially relatively well-off Americans like my ...

http://www.salon.com/2013/07/16/what_you_need_to_know_before_brushing_your_teeth_partner/