From the same WHO site that the apparent graph was taken “The level of dental caries (measured as the mean number of Decayed, Missing or Filled teeth) falls from seven at a fluoride concentration of 0.1 mg l–1 to around 3.5 at a fluoride concentration of 1.0 mg l–1. As fluoride concentration increased further (up to 2.6 mg l–1) dental decay continues to fall, but only slightly (Dean, 1942; USPHS, 1991). Conversely, dental fluorosis increases as fluoride concentration increases. At a fluoride concentration of 1 mg l–1 about 20 per cent of children have evidence of dental fluorosis but this fluorosis is of a mild degree of severity and would not be cosmetically obvious to the children or their parents (Dean, 1942)”

http://www.who.int/water_sanitation_health/publications/fluoride_drinking_water_full.pdf

There is also fluoride in all natural food products (even organic) so if you believe this documentary please don’t continue eating (or drinking) ANYTHING as you may die of fluoride exposure.
And please go tell everybody that “The Nazis are putting fluoride in our drinking water to control our minds and make us all stupid”