Here is what the NRC wrote concerning the prevalence of severe dental fluorosis:
Despite the wide range of research methods, fluorosis indexes, water
fluoride measurement methods, and population characteristics in these studies conducted over a period spanning half a century, a clear trend is evident. The prevalence of severe enamel fluorosis is close to
zero in communities at all water fluoride concentrations below 2 mg/L. (NRC 2006; Page 93)
This is entirely untrue, and the Review itself lists numerous studies documenting
exactly the opposite (i.e. Yoder et al, 1998). Already in 1993, the NRC wrote the following concerning severe dental fluorosis in Augusta, Georgia:
"More recently, a prevalence of 80.9 was reported in children 12-14 years old in
Augusta, Georgia, the highest prevalence yet reported in an optimally fluoridated community in the United States (Williams and Zwemer, 1990)....moderate-to-severe fluorosis was found in 14% of the
children"- (1993 NRC Report, Page 37).
A basic overview of the literature indicates that the NRC Committee engaged in
"selected use of data".
A recent review about the prevalence of dental fluorosis in Mexico (Soto-Royas et al., 2004) provides
detailed figures from various studies conducted in Mexico: