I’ve been doing it wrong

To rinse or not to rinse. That is the question.

Or, more fully, when you brush your teeth, do you rinse the excess toothpaste out of your mouth with water?

I’d never really thought about this question before Wednesday, when a tooth-related incident in my house brought the different toothbrushing strategies to light. One flatmate, after brushing his teeth, turned the tap on, gathered some water in a cupped hand, and rinsed his mouth out. My other two flatmates were aghast.

“Why are you rinsing!? You’re not supposed to rinse! Jon, get in here, he’s rinsing!”

I ran in to the bathroom and my life changed forever.


Before reading further, take a moment and answer the question. Do you rinse after brushing your teeth, or just spit out the excess toothpaste?

Now that you’ve identified as a rinser or a spitter, prepare to either have your world shaken or to get on the highest horse in the land.


I was surprised by this strong reaction, but I was even more surprised that they had an issue with him rinsing because I’d been rinsing my whole life.

I’m a rinser.

In that moment, I couldn’t believe that I might have been doing something as fundamental as brushing my teeth wrong my whole life. So I did what most 20-somethings with a science blog would do. I got out my laptop and started googling. And I found this official NHS page: How to keep your teeth clean.

It starts off pretty uncontroversial: “Brush your teeth with fluoride toothpaste twice a day for about two minutes to help keep your teeth and mouth healthy.” Great. I do that. So far, so good. But I scrolled down and there was a heading that sent a shiver down my spine.

Don’t rinse with water straight after toothbrushing

“After brushing, spit out any excess toothpaste. Don’t rinse your mouth immediately after brushing, as it will wash away the concentrated fluoride in the remaining toothpaste, thus diluting it and reducing its preventative effects.” Uh oh.

According to several UK sources (like section 2 of this report on Delivering better oral health), I’ve been brushing my teeth wrong my whole life. And there’s a pretty decent chance you have too.

It might just be a British thing, I thought to myself. So I started doing searches for Canadian, American and Australian dental advice.

Canadian advice (like this Canadian Dental Association page on tooth brushing) generally doesn’t say anything about rinsing. Australian advice actually encourages rinsing with mouthwash, something explicitly condemned by the Brits. The Americans are mostly silent on the topic, although I did find an American Dental Association page on mouthwash that implies it’s ok to rinse with mouthwash after brushing, depending on what the bottle says.

So why do Brits care so much about leaving some toothpaste on their teeth?

I have a theory: it’s all about fluoridated water.


The shiny, strong part of a tooth is called enamel, and it’s made mostly of hydroxyapatite. The problem is that in an acidic environment, like your mouth after a cup of coffee, the hydroxy part of the mineral is drawn out and your teeth essentially start to dissolve. Sugar-loving bacteria that live in your mouth also secrete acid as a by-product, which is why sugary foods cause cavities.

But if you put fluoride on your teeth, it can replace the part that the acid dissolved, strengthening your teeth. Fluoride also helps your teeth rebuild and might help kill some of the nasty bacteria. But fluoride can only penetrate a small distance into a tooth, so it’s quite easy to rub off. In order for it to be effective, you need to use it all the time. Twice or more a day, in fact.

To make it easier to get a consistent, low-level exposure to fluoride, governments across the world started adding it to tap water. This was (and continues to be) quite controversial, but if the World Health Organization, Health Canada, expert panels, the CDC and the majority of dentists and scientists agree that it does more good than harm, it’s hard not to be convinced.

The experiment in water fluoridation started in 1945 in the US, with Grand Rapids, Michigan. After 11 years, it was announced that the rate of tooth decay in children in the city had dropped 60% compared to the nearby control city of Muskegon, Michigan.

Canada, where I’m from, got on the fluoride bandwagon pretty early. In the same year that Grand Rapids started its experiment, 1945, Brantford became the first Canadian city to fluoridate water. In due course they saw the same reductions as their American counterparts. Since then, water fluoridation has taken off. 45% of the Canadian population lives with fluoridated water, with many of the major cities getting on board (Ottawa, Toronto, Hamilton, Winnipeg, Calgary, Edmonton and Halifax have fluoridated water, Montreal and Vancouver are notable non-fluoridaters).

Water fluoridation is the official policy of the US Public Health Service, so more than two thirds of Americans have fluoride in their tap water. Australia is even stronger on fluoridation, with their rate pushing 70%. Europe, by comparison, barely fluoridates their water. The only 4 countries that have any fluoridation programs are Spain, Serbia, Ireland and the UK, but less than 10% of the population of these countries have that water.

In the UK, most of the fluoridation happens in the North and in the Midlands. In total, about 6 million people have access to fluoridated water in the UK.

To rinse or not to rinse

So what does all this mean for rinsing after brushing?

My theory is that, in places (like the UK) where water fluoridation is rare, health authorities advise people to leave toothpaste on their teeth because toothpaste is the only major source of fluoride. In places where fluoride is abundant in the water, health authorities don’t really care whether you get extra fluoride from brushing your teeth.

I accept that I’m doing it wrong. While I’m living without fluoridated water, I accept that I should probably become a spitter rather than a rinser. After about a week of trying though, I can tell you that changing a lifelong habit is really hard. There’s probably some interesting science behind that, but I’ll leave it for another time.


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