By Emma Yasinski
The most recent data from the National Health and Nutrition Examination Survey (NHANES) suggests that prevalence of fluorosis – markings on the teeth caused by long-term exposure to excess fluoride – increased in children from the period 1999-2004 to 2011-2016. Anti-fluoridation advocates contend the data prove that U.S. water is over-fluoridated.
But many dentists were left scratching their heads over the findings.
Johnny Johnson, Jr., DMD, a pediatric dentist in Florida who heads a group that advocates for community water fluoridation, told Incisor he received a flurry of phone calls from dentists disputing the NHANES findings, saying that they have not observed any such increases in their practices.
Shortly after, the CDC published an analysis explaining the flaws in the NHANES survey methodology that led the work to suggest a dramatic increase in fluorosis, which, the CDS said, is not only unlikely but doesn’t make sense biologically.
Severe dental fluorosis, which can damage enamel and put patients at risk for further tooth decay, is very rare in the U.S. The survey looked for signs of mild-to-moderate fluorosis which Howard Pollick, BDS, MPH, a dental professor of the University of California, San Francisco, and American Dental Association spokesperson, explained to Incisor, does not adversely impact health, but can be visible on the teeth.
Fluorosis happens when patients under the age of eight consistently consume too much fluoride, which can be found in tap water, toothpaste, mouthwash, and supplements. “It's not going to happen because you swallow a lot of fluoride one time,” said Dr. Pollick. Additionally, once fluorosis is present, it doesn’t progress; it doesn’t get better, nor does it get worse.
Dentists recognize fluorosis by identifying whitened spots on an individual’s teeth. Generally, these spots will show up on the same teeth on each side of the mouth, suggesting that the exposure occurred while those teeth were developing.
The NHANES survey is conducted every two years to assess various aspects of health, including fluorosis levels. It asks dentists to evaluate the teeth of patients in different age groups meant to be a representative sample of the overall U.S. population.
In the most recent survey, NHANES reported notable increases in the prevalence of fluorosis.
However, there can be other reasons for the discoloration. Dr. Johnson explained that many conditions, including dehydration and celiac disease, can cause marks on teeth that look like fluorosis. Plus, the identification of mild-to-moderate fluorosis can be highly subjective.
The analysis by the CDC studied the data showing examinations from different dentists on the same patient’s teeth. The level of agreement ranged from “moderate” to “almost perfect.” But the scores that were shown for individual teeth showed greater variability.
“The difference in DFI [Dean’s Fluorosis Index] values for the same teeth assessed in the same way days apart, however, indicates the subjective nature of the DFI scoring method,” the study authors wrote.
Then, the researchers conducted a cohort analysis on the data from NHANES 2001–2004 and 2011–2014. The CDC found that 9.5 percent of 6-9 year-olds in 2001-2004 showed fluorosis, but when that same group was 16-19 years old in 2011-2014, the prevalence had increased to 46.9 percent. The CDC explained that the difference in fluorosis between age groups was not logical. Since fluorosis occurs in childhood and does not change in adulthood, the prevalence of fluorosis in the sample of children from the earlier survey should match the sample of adults in the later ones.
“It's not biologically plausible to see that major of a shift in moderate to severe fluorosis as the data is showing from the NHANES,” said Dr. Johnson.
There are some areas, mostly outside of the U.S. or where people drink well water, where rates of moderate to severe fluorosis are higher. Dr. Johnson explained these areas have fluoride levels of four to 16 milligrams per liter (mg/L) as opposed to the national U.S. average of one to three mg/L.
New methods may improve surveys going forward, but in the meantime, “I don't think dentists have to be concerned,” said Dr. Pollick. “If they see a child with dental fluorosis, then they should inquire, ‘where do you live? where are you drinking water?’” and adjust their recommendations accordingly.
Author: Contributing writer Emma Yasinski received her Master of Science (MS) in science and medical journalism from Boston University. Her articles have also appeared at TheAtlantic.com, Kaiser Health News, NPR Shots, and Genetic Engineering and Biotechnology News.
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