the effect of water fl uoride concentration on dental caries and fl uorosis in fi ve iran provinces: a multi-center two-phase study

background: water fl uoride level is unknown in many regions of iran. besides, only few noncontrolled studies world-wide have assessed the effect of water fl uoride on dental fl uorosis and caries. we aimed to measure the fl uoride level of 76 water supplies in 54 cities and evaluate the effect of fl uoride on dental caries and fl uorosis in a large multi-project study. materials and methods: in the fi rst phase (cross-sectional), fl uoride levels of 76 water tanks in 54 cities/villages in fi ve provinces of iran were randomly evaluated in fi ve subprojects. in the second phase (retrospective cohort), 1127 middle school children (563 cohort and 564 control subjects) in the high and low ends of fl uoride concentration in each subproject were visited. their decayed, missing and fi lled teeth (dmft) and fl uorosis states were assessed. the data were analyzed using chi-square, mann-whitney u and independent-samples t -test (α = 0.05). results: mean fl uoride level was 0.298 ± 0.340 mg/l in 54 cities/villages. only eight water tanks had fl uoride levels within the normal range and only one was higher than normal and the rest (67 tanks) were all at low levels. overall, a signifi cant association was observed between fl uoride level and fl uorosis. however, this was not the case in all areas, as in 2 of 5 provinces, the effect of fl uoride on fl uorosis was not confi rmed. in 4 of the 5 areas studied, there was a signifi cant link between fl uoride level and dmft. conclusion: extremely low fl uoride levels in iran cities are an alarming fi nding and need attention. higher fl uoride is likely to reduce dental caries while increasing fl uorosis. this fi nding was not confi rmed in all the areas studied. key words: community fl uorosis index, dean’s fl uorosis index, dental caries, dental fl uorosis,water fl uoride