Dental fluorosis–a major, but preventable, oral diseases and public oral health problems–related with exceeded the fluoride level in natural groundwater sources. Dental fluorosis remains as a major public health problem worldwide, including Vietnam. Previous studies carried out since the 2000s demonstrated a link between dental fluorosis and increased fluoride levels in drinking water of Ninh Hoa town, Khanh Hoa province. The aim of this study was to determine the temporal variation of district’s population, who at risk for dental caries or dental fluorosis, with questionair survey in Ninh Hoa town. The results indicated that the rate of population at risk for dental fluorosis, has been decreased in comparision with previous studies. In especially, in the vulnerable area with high fluorid zones like Ninh Xuan, Ninh Phung wards (> 6mg/L), the number of population at risk decreases to only 18 and 12%, respectively. Overall, only 25% district’s population were risk of potential dental fluorosis. It is the results from implementation of drinking water supply projects from government. However, the long-term operation of the replacement of groundwater project need to be further strengthened. In addition, a further study on dental fluorosis and sources of F should be carried out.