In a five-year, NIH-funded study of 686 older adults, flossers lost about one tooth and non-flossers lost about four.1 Flossers also averaged roughly three fewer missing teeth overall, with less gum disease between the teeth and fewer cavities. Flossing was self-reported, and the finding is an association, not proven causation.
What did the five-year study actually find?
Over five years, flossers lost about one tooth and non-flossers lost about four.1 Most flossing research measures things you can't see or feel: plaque scores, gum-pocket depths, inflammation indexes. Useful to clinicians, abstract to everyone else. That's what makes a 2020 study in the Journal of Dental Research stand out: it measured teeth. Specifically, how many of them people still had.
Researchers at the University of North Carolina followed 686 older adults in the Piedmont 65+ Dental Study (average age about 73) for five years, comparing people who reported flossing with people who didn't.1 Over those five years, the flossers lost about one tooth. The non-flossers lost about four.
Over five years, flossers lost about 1 tooth. Non-flossers lost about 4, and flossers averaged roughly 3 fewer missing teeth overall.
The gap didn't start at the finish line, either. Across the whole study, flossers averaged roughly three fewer missing teeth than non-flossers. And this wasn't a raw comparison of two casually different groups: the researchers adjusted for race, sex, age, diabetes, smoking, education, brushing habits, and how often people actually visited a dentist. The tooth-loss gap held.
Was it only tooth loss?
No. Underneath the headline number, the same study found the pattern you'd expect if flossing were doing real work: flossers had significantly less periodontal disease between their teeth (the exact zone floss is designed to reach), with deep attachment loss at about 38% of interproximal sites versus about 49% in non-flossers.1 They also had fewer cavities.
That coherence matters. Gum disease is the leading pathway to losing teeth in adults (a chain we walk through in gum disease and tooth loss), and in this study, the people with the interdental habit had less disease in the interdental zone and kept more teeth. The pieces point the same direction.
What are the caveats?
Three, and none is small: the study covered only older adults, flossing was self-reported, and the result is an association rather than proven causation.
First, this is a study of older adults. Every participant was 65 or older, most in their early seventies. That's a population where tooth loss happens fast enough to measure in five years, and where, by the CDC's count, roughly 60% have gum disease.2 The findings describe older adults; they can't simply be stretched to cover a 30-year-old. We say "in older adults" because that's what the data supports.
Second, flossing was self-reported. Nobody watched these participants floss for five years: people said whether they flossed, and researchers took them at their word. Self-reports of virtuous habits are imperfect, which is a limitation worth naming even when the outcome (a tooth is there or it isn't) is about as objective as dental research gets.
Third, and most important: this is an association, not proven causation. An observational study can't randomly assign people to floss or not floss for five years, so it can't prove flossing caused the difference. People who floss may differ from people who don't in ways no statistical adjustment fully captures: conscientiousness, diet, health attention generally. The adjustments for smoking, diabetes, brushing, and dental visits narrow that gap considerably. They cannot close it.
Why is this study still worth your attention?
One more detail, and it's a credibility feature rather than a footnote: this research was funded by the National Institutes of Health, and the authors declared no conflicts of interest.1 No floss maker, no device manufacturer, no dental-products company paid for the result. In a field where a surprising amount of the tool research is industry-funded, a conflict-free, government-funded, five-year study with a hard outcome is rare, and it's exactly the kind of source this library is built on.
So here's the honest summary. In older adults, flossing was associated with keeping roughly three more teeth, less gum disease between the teeth, and fewer cavities, in a five-year study with no industry money behind it. That's not proof of cause and effect, and we won't pretend it is. But as evidence goes, "the people with the habit kept their teeth" is about as plain as the case for flossing gets, and it fits the broader pattern of large national surveys linking interdental cleaning to less gum disease.
Common questions
Does this study prove that flossing saves teeth?
No. It's an observational study, so it can't prove flossing caused the difference. Researchers adjusted for race, sex, age, diabetes, smoking, education, brushing habits, and how often people visited a dentist, and the tooth-loss gap held.1 Adjustment narrows the gap rather than closing it, so the honest word is associated.
Does the finding apply to younger adults?
The data doesn't support stretching it that far. Every participant was 65 or older, most in their early seventies, a population where tooth loss happens fast enough to measure in five years, and where roughly 60% have gum disease by the CDC's count.2 The finding describes older adults because that's who was studied.
Who funded the study?
The National Institutes of Health, and the authors declared no conflicts of interest.1 No floss maker or device manufacturer paid for the result. In a field where a lot of the tool research is industry-funded, a conflict-free, government-funded, five-year study with a hard outcome is unusual.
How was flossing measured in the study?
By self-report. Nobody watched participants floss for five years; people said whether they flossed, and researchers took them at their word.1 Self-reports of virtuous habits are imperfect, though the outcome measured, whether a tooth is still there or not, is about as objective as dental research gets.
Does other evidence point the same way?
Yes. Large national surveys link regular interdental cleaning to less gum disease, with the most frequent cleaners showing the least severe disease. That is a different kind of data pointing in the same direction, covered in regular interdental cleaning and lower odds of gum disease. Both are associations rather than proof of cause and effect.
- Marchesan JT, et al. Flossing is associated with improved oral health in older adults. Journal of Dental Research, 2020;99(9):1047–1053. doi:10.1177/0022034520916151. PMC7375740. Piedmont 65+ Dental Study, n=686, mean age ~72.7, 5-year follow-up. NIH-funded; no declared conflicts. Self-reported flossing; observational association.
- Eke PI, et al. / CDC. Periodontitis prevalence among US adults, NHANES 2009–2014; NIDCR data pages (2024). ~60% of adults 65 and older.