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Ask Tufts Experts July 2015 Issue

Q. My dentist recommended using a prescription fluoride toothpaste. If the water in my city is already fluoridated, does that contribute to the risk of possible overdose?

A. Public Health Dentist Wanda Wright, DDS, and Associate Clinical Professor David Leader, DMD, posed this question to Tufts University School of Dental Medicine Dental/Public Health students. Their short answer is that using prescription fluoride toothpaste in communities with water fluoridated at the usual 0.7 to 1.0 parts per million (PPM) will not contribute to the risk of an overdose.

They explain, “Fluoride reaches a toxic level only at 2.5 to 5 grams per kilogram (2.2 pounds) when consumed within two to four hours. That means that an adult would have to ingest hundreds of gallons of community-fluoridated water within a few hours to cause harm. If you were to try to drink that much water so quickly, you would die from the effect of the water before the fluoride could reach a toxic level. It is very important to note the two- to four-hour time frame. Consuming less fluoride over time does not create an additive effect.

“How much water is a toxic dose? In 2007, a 28-year-old woman died after swallowing only 6 liters (6.34 quarts) of water in a contest. That water might have contained 6 milligrams of fluoride. The additional fluoride of prescription toothpaste, if you were to swallow all of the prescription toothpaste on a toothbrush, might be as high as 2 milligrams per use. That means that if this woman also used prescription fluoride toothpaste in that time, she may have ingested as much as 8 milligrams of fluoride in 24 hours. That is a small percentage of an acutely toxic dose for an adult. Please note that we do not recommend prescription fluoride toothpaste for children under seven years old.”

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