The study referred to by Earl Howe is open to criticism.

The study referred to by Earl Howe is open to criticism. 

The authors themselves note: "it is accepted that a cross sectional study is not the most robust design for assessing the impact of water fluoridation. However, the cost implications for a study design that would include prospective monitoring of birth cohorts, serial cross sectional surveys that include analysis of diet and total fluoride intake with anthropometric measurements would be cost prohibitive and beyond the scope of this project. Nevertheless, the aforementioned are important considerations to be taken during study design." 

They also note that  children in Manchester were more likely to not rinse after brushing their teeth and therefore more likely to swallow their toothpaste - hence the higher fluorosis levels. Full paper available at:

http://www.biomedcentral.com/1471-2458/12/1122/

Stephen