Why Do We Brush Our Teeth for Two Minutes?

Why two minutes? Why not one, three or five?

There is nothing obviously natural about 120 seconds, so there must have been a randomised controlled trial (RCT) sometime indicating that two minutes was the appropriate amount of time to brush. Well, it turns out the story isn’t that simple.

A little help with the research

Cards on the table: I had some help with the research using ChatGPT, Claude and Gemini to search the literature. I’m not the kind of person who takes their answers as fact, but the fact is they are better and quicker than I am at trawling the archives, finding papers, archive references, possible citation trails and promising explanations for where the two-minute recommendation came from.

Some of the leads were spot on, others turned out to be unsupported, misattributed or simply wrong when I tried to verify them.

We all know an AI-generated explanation isn't evidence. Where a claim matters, I've tried to trace it back to a paper, contemporary document or other source that can be checked independently. There are gaps which I’ve left rather than filling with a plausible story made up by my research assistants.

Does two minutes actually work?

Before looking for the origin of the recommendation, shouldn’t we check that this isn't simply folklore?

There is good evidence that brushing duration affects plaque removal. In 2009, Creeth and colleagues had 47 subjects brush for periods between 30 and 180 seconds. Plaque removal increased with brushing time and tended towards a maximum at longer durations. Brushing for 120 seconds removed 26% more plaque than brushing for 45 seconds.[1]

Tellingly, the researchers described two minutes as the existing “consensus minimum”, so the experiment provided evidence supporting existing best practice.[1]

This isn't an argument that dentists have got it wrong. Far from it, two minutes appears to be a perfectly reasonable practical recommendation. No, this is about where the number came from!

Looking for the original evidence

I expected to find an early experiment comparing different brushing times — perhaps the RCT I imagined earlier — followed by a recommendation based on the results: experiment, evidence, recommendation. That's broadly how we'd expect medical science to work.

There are experiments of this kind. Hawkins and colleagues published a paper explicitly titled Duration of toothbrushing for effective plaque control in 1986.[2] Unfortunately, I haven't been able to access the paper, so I can't examine its findings.

The problem is that two minutes was already in use well before then.

In 1979, De la Rosa and colleagues studied plaque growth and removal in 180 teenage boys. The subjects brushed their teeth under supervision for two minutes each day.[3] The researchers weren't comparing different brushing durations; two minutes was simply part of the experimental protocol.

That distinction matters. By 1979, two minutes was sufficiently unremarkable to be specified as the brushing period without being the thing under investigation.

British researchers were also studying how long people actually brushed. Macgregor and Rugg-Gunn secretly recorded 85 uninstructed English schoolchildren aged 11 to 13 brushing their teeth. Might not get past the ethics committee today. Their mean brushing time was 60.3 seconds.[4]

And I have a little piece of decidedly non-scientific evidence of my own: by then I was being taught the two-minute rule by my dentist and at a British primary school.

So, like me, you're probably thinking the answer must lie further back than the 1970s.

Two minutes in about 1940

The American Dental Association (ADA) has digitised a fascinating collection of patient education material dating from 1929 onwards.[5]

Among it is a leaflet called When, What to Use, How to Brush Your Teeth. The document itself is, unfortunately, undated; the ADA catalogue assigns it an approximate date of 1940, so we have a reasonable idea when it was published but the date shouldn't be treated as exact.[6]

Its advice, however, is unambiguous:

“Teeth should be brushed after each meal, and for at least two minutes.”[6]

That moves the documented recommendation back nearly four decades before the duration experiments I had initially been looking at and well before randomised controlled trials became established in modern medicine.

Incidentally, the idea of random allocation itself is much older. Jan Baptist van Helmont, a Flemish chemist and physician, proposed in the seventeenth century that patients should be allocated by casting lots to compare treatments for fever. The proposal was published in 1648, although the trial was apparently never carried out.[8]

At first sight this looks like it may be the answer: the two-minute rule is much older than I imagined. But another document in the same archive complicates the story.

Or perhaps three minutes?

In 1945, the ADA's Bureau of Public Relations distributed The Why and How of Tooth Brushing, by Isadore Hirschfeld.[7] The document carries the printing code 3-45, giving us a much firmer date than we have for the earlier leaflet.

Its advice is different. Once the correct technique has been learnt, it says, oral hygiene requires “about three minutes”. More interestingly, it contains a section headed How Long to Brush which argues that timing brushing in minutes is itself unsatisfactory because someone might spend most of the allotted time on a favoured part of the mouth. That’s actually quite a good point. I’m pretty sure I read once that dentists can often tell whether a patient is left- or right-handed by looking at their teeth, although that may be apocryphal.

Instead, it recommends a specified number of strokes in each area. For an average mouth, it says, this should require no more than three minutes.[7]

So within a few years we have educational material associated with the same professional organisation saying two different things: at least two minutes in the document catalogued around 1940, and about three minutes in 1945, with the latter actually questioning whether brushing should be timed in minutes at all.

Whatever the origin of the two-minute rule, it doesn't look as though it had become an immutable standard in the 1940s.

What happened in Britain?

This is the part of the story I haven't yet been able to unravel.

We know that English researchers were measuring children's brushing behaviour by the end of the 1970s.[4] We know that two minutes was being used as an experimental brushing period by 1979.[3] And I know from personal experience that the two-minute recommendation was being given to at least some British children during the same decade.

What I haven't found is the contemporary British evidence explaining where that advice came from or why the duration was two minutes.

There is an interesting lead, however. On 25 November 1971, the Health Education Council convened a Conference on Dental Health Education in London with the support of the General Dental Council and the British Dental Association. A consolidated report of the conference survives in the Wellcome Collection as K48955, ISBN 0903652005.[9]

Unfortunately, it hasn't been digitised. When I contacted the Wellcome Collection, they told me that it is held in closed stores and currently has to be consulted in person. The collection also holds Health Education Council archive material from the 1970s concerning dental-health education and research into dental-health education for teenagers, some of which is similarly unavailable remotely.

So part of the answer may be sitting on a shelf in London. I live and work in France, so a visit isn’t something I’ll be able to make anytime soon.

It’s a long shot, I know, but if anyone reading this happens to be visiting the Wellcome Collection and has an appetite for obscure research questions, I'd be very keen to know whether this material says anything about how long people were being advised to brush their teeth, particularly if it mentions two minutes or, even better, where that recommendation came from. You never know.

Recommendation first, evidence later?

Recall the ADA's changing advice: at least two minutes in material catalogued to around 1940, then about three minutes — with doubts about timing by minutes at all — in 1945.[6][7] Much later, experimental evidence provided good reasons for the two-minute recommendation.[1]

What I haven't found is the evidence that originally produced the number.

Perhaps it exists somewhere in the early dental literature. Perhaps two minutes emerged from accumulated professional experience rather than a particular experiment. Perhaps it was originally a convenient instruction that survived because it worked well enough at the time and was subsequently supported by better evidence.

At the moment, I don't know. And maybe that is more interesting than pretending that I do.

This investigation was of genuine interest to me, and there are obvious parallels with my day job and my customers' needs. Computer systems accumulate numbers in much the same way: timeouts, thresholds, polling intervals, configuration parameters, etc.

Ask why a parameter is set to 8191 and perhaps there are good reasons for choosing it. Sometimes there was a compelling reason five years ago that no longer applies. The monthly report that gathers dust unread on the shelf until the next one is printed is another prime example. And I'm sure everyone reading has a personal favourite along the lines of: “…but we’ve always done it that way…” Why?

That doesn't mean 8191 is necessarily wrong. The value works, but that doesn't mean it's still optimal, or that the original reason for choosing it remains valid. If we no longer know why a decision was made, it becomes much harder to judge whether changing circumstances should change the decision. A randomised controlled trial, perhaps?

Two minutes of toothbrushing appears, at least so far, to follow this familiar pattern.

And until I find better evidence, I'll continue brushing for at least two minutes.

References

1. Creeth JE, Gallagher A, Sowinski J, Bowman J, Barrett K, Lowe S, Patel K, Bosma ML. “The effect of brushing time and dentifrice on dental plaque removal in vivo.” Journal of Dental Hygiene. 2009;83(3):111–116. PMID 19723429.
2. Hawkins BF, Kohout FJ, Lainson PA, Heckert A. “Duration of toothbrushing for effective plaque control.” Quintessence International. 1986;17(6):361–365. PMID 3460112. Not consulted: full text is not freely accessible.
3. De la Rosa M, Zacarias Guerra J, Johnston DA, Radike AW. “Plaque growth and removal with daily toothbrushing.” Journal of Periodontology. 1979;50(12):661–664. doi:10.1902/jop.1979.50.12.661.
4. Macgregor IDM, Rugg-Gunn AJ. “Survey of toothbrushing duration in 85 uninstructed English schoolchildren.” Community Dentistry and Oral Epidemiology. 1979;7(5):297–298. doi:10.1111/j.1600-0528.1979.tb01235.x.
5. American Dental Association. Patient Dental Health Education Materials 1929–1981. ADA Library & Archives digital collection.
6. American Dental Association. When, What to Use, How to Brush Your Teeth. Undated; catalogued by the ADA as approximately 1940. The ADA notes that the date is approximate.
7. Hirschfeld I. The Why and How of Tooth Brushing. American Dental Association, Bureau of Public Relations, 1945.
8. Wikipedia contributors. “Randomized controlled trial — History.” Wikipedia, The Free Encyclopedia. https://en.wikipedia.org/wiki/Randomized_controlled_trial#History. Accessed 30 September 2026.
9. Health Education Council. Consolidated report of the Conference on Dental Health Education, London, 25 November 1971. Conference convened by the Health Education Council with the support of the General Dental Council and British Dental Association. ISBN 0903652005. Wellcome Collection K48955. Not consulted: the item has not been digitised and currently requires consultation in person.