"Fluoride-containing compounds are used in topical and systemic fluoride therapy for preventing tooth decay. They are used for water fluoridation and in many products associated with oral hygiene. Originally, sodium fluoride was used to fluoridate water; however, hexafluorosilicic acid (H2SiF6) and its salt sodium hexafluorosilicate (Na2SiF6) are more commonly used additives, especially in the United States."

"DRI Tables"

"Recommended Dietary Allowances (RDA) - The daily dietary intake level of a nutrient considered sufficient by the Food and Nutrition Board to meet the requirements of 97.5% of healthy individuals in each life-stage and sex group. It is calculated based on the EAR and is usually approximately 20% higher than the EAR. ... Tolerable upper intake levels (UL) - To caution against excessive intake of nutrients (like vitamin A) that can be harmful in large amounts. This is the highest level of daily consumption that current data have shown to cause no side effects in humans when used indefinitely without medical supervision."