Aim: This was to study the prevalence of dental fluorosis in a Swedish city (Uppsala) with natural 1-1.2 ppm F in drinking water. It was also to compare the prevalence of idiopathic enamel disturbances (Morbus S) in children born in Uppsala with the prevalence in children who had moved in to Uppsala at an age when the Uppsala water could not have influenced the development of Morbus S.
Methods: Children born in 1970 and 1967 in Uppsala (Sweden) on even days (n=840) were invited to the study. All children not born in Uppsala were included (n=475), 24 children refused to take part and 45 were sick or had moved. Four examination teams performed the examinations after calibration against a "gold standard". Dental fluorosis was determined by the criteria of Dean , idiopathic white spots according to Nevitt et al.  and Morbus S was diagnosed according to Forsman .
Results: Children born in Uppsala had a higher prevalence and severity of fluorosis compared with those not born in Uppsala. It was found that 40 out of the 715 children born in Uppsala had enamel disturbances according to criteria for Morbus S and the corresponding figures for children not born in Uppsala were 33 out of 486.
Conclusion: The specific enamel hypomineralisations type Morbus S cannot be connected to intake of fluoride.