America's prevention effort reaches the half of the mouth a toothbrush already cleans. Only about 1 in 3 US adults report flossing daily,2, 3 brushing alone removes only up to about 60% of plaque,1 and about 42% of American adults over 30 have some form of gum disease.4 The neglected half is the space between the teeth.
The habit America bought, and the one it skipped
Brushing was only ever half the job, and it's the half America bought. By almost any measure, teaching Americans to brush was one of the most successful health campaigns ever run: brushing is automatic, unquestioned, built into mornings and bedtimes. But it cleans only the surfaces a brush can touch, and a peer-reviewed review estimates that brushing alone removes only up to about 60% of plaque.1 The rest sits between the teeth, exactly where most gum disease and between-teeth decay begin. We unpack that finding in brushing is not enough.
The other half of the job, cleaning between the teeth, got the same decades of professional advice. It didn't take. This article is about how completely it didn't take, and why the gap keeps hiding in plain sight.
What do people say they do?
Only about 1 in 3 US adults report flossing every day, according to CDC NHANES data, a number that has barely moved across more than a decade of measurement.2, 3 The government's own surveys tell that story plainly. And because the data is self-reported, and people tend to overstate habits they know they're supposed to have, the true figure is likely lower still. The full picture (including how unevenly the habit is distributed) is in only about 1 in 3 adults floss daily.
What do people actually buy?
Roughly 12 powered toothbrushes for every water flosser: that is what one national oral-care distributor's fifteen years of sales records show, spanning hundreds of thousands of devices sold through insurance channels.5 Survey answers are what people say; sales records are what people do with their money, and here the gap stops being an abstraction.
For every dozen powered toothbrushes America buys, it buys roughly one device for cleaning between the teeth.
Read that ratio next to the survey data and the two measurements rhyme. Two out of three adults say they don't floss daily; the market, buying twelve brushing devices for every flossing device, is voting the same way with its wallet. When employers, insurers, and families invest in oral-health prevention, the money overwhelmingly flows to the half of the mouth that's already being cleaned.
What shows up in the disease data?
The neglect shows up: by the CDC's own measurement, about 42% of American adults over 30 have some form of gum disease.4 If the between-teeth spaces really were the neglected half, that is exactly what you'd expect to find. Set the three numbers side by side:
Brushing: near-universal, and it removes only up to about 60% of plaque.1 Interdental cleaning: practiced daily by roughly one in three.2 Gum disease: present in about 42% of adults over 30.4 These are associations, not a controlled experiment, and gum disease has more than one cause. But the strongest independent evidence points the same direction: regular interdental cleaning is associated with less gum disease, and it targets precisely the surfaces brushing leaves behind. More on the prevalence numbers in how common is gum disease.
Why do prevention programs keep repeating the miss?
Wellness programs, benefit designs, and dental-aisle promotions overwhelmingly reach for the same object: a better toothbrush. It's the familiar purchase, the established habit, the safe recommendation. So the prevention dollar keeps upgrading the half of the mouth that was never the problem, while the half where most disease begins (the between-teeth spaces) stays unaddressed for two out of three adults. Doing the same thing and expecting the disease numbers to move is exactly the loop the data says we're stuck in. Whichever tool a person prefers (and we compare them honestly in string floss vs. water flosser), the gap won't close until prevention effort actually reaches the interdental habit.
An honest closing note on the sales data
That 12-to-1 ratio comes from a single distributor's first-party records, specifically Z Dental's, the company that supports this library, which is exactly why we label it carefully: a large, real-money dataset spanning fifteen years, but one company's channel, not a national census of device sales.5 This site labels its evidence carefully, so: treat it as an indicator, not a definitive market statistic. What makes it worth publishing is how precisely it rhymes with the independent government data: the surveys say two-thirds of adults skip the daily interdental habit, and the sales ledger shows the market buying as if that's true. Three separate measurements (what people report, what people buy, what shows up in their gums), and one consistent gap. Closing it is this site's entire reason to exist.
Common questions
Is the 12-to-1 ratio a national statistic?
No. It comes from a single distributor's first-party sales records, a large, real-money dataset spanning fifteen years, but one company's insurance channel rather than a national census of device sales.5 Treat it as an indicator rather than a definitive market statistic. What makes it worth publishing is how closely it rhymes with the independent government survey data.
How much plaque does brushing actually leave behind?
A peer-reviewed review estimates that brushing alone removes only up to about 60% of plaque at each episode.1 The remainder concentrates in the spaces between the teeth, exactly where most gum disease and between-teeth decay begin (unpacked in brushing is not enough).
Why do prevention programs keep favoring toothbrushes?
Because a better toothbrush is the familiar purchase, the established habit, and the safe recommendation. So the prevention dollar keeps upgrading the half of the mouth that was never the problem, while the between-teeth spaces stay unaddressed for two out of three adults.
Does this prove that skipping flossing causes gum disease?
No. These are associations, not a controlled experiment, and gum disease has more than one cause. What the strongest independent evidence shows is that regular interdental cleaning is associated with less gum disease, and that it targets precisely the surfaces brushing leaves behind.
Which interdental tool should a prevention program choose?
The evidence supports the habit more strongly than any particular tool, so the choice of device matters less than whether people adopt the habit at all. We compare the options in string floss vs. water flosser. The gap won't close until prevention effort actually reaches the interdental habit, whichever tool carries it.
- Ng E, Lim LP. An overview of different interdental cleaning aids and their effectiveness. Dentistry Journal, 2019. PMC6630384. Review estimate: brushing alone may remove only up to ~60% of plaque.
- Fleming EB, et al. Prevalence of daily flossing among adults, NHANES 2011–2014. Journal of Periodontology, 2018. CDC authors. PMC6434526. Self-reported survey data.
- Liang L, Aris IM. Minimal changes in daily flossing behavior among US adults from 2009 through 2020. Journal of the American Dental Association, 2024. PubMed 38752966. Self-reported survey data.
- Eke PI, et al. / CDC. Periodontitis prevalence among US adults, NHANES 2009–2014; NIDCR data pages (2024).
- Z Dental first-party distribution data, 1997–2026: ratio of powered toothbrushes to water flossers sold across insurance-channel distribution (full analysis to be published at zdental.com/evidence/the-flossing-gap/).