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Comment by barbegal | Hacker News Reader

I tried to find studies for the effects of teeth brushing frequency but the only ones I could find were cohort analyses as opposed to randomised trials. It seems like despite a lack of evidence, it would be very hard to ethically approve a randomised trial of teeth brushing over a long period. I honestly believe brushing teeth twice a day is very much a ritual which achieves very little on a per effort basis.

Reducing our intake of sugary and acidic foods and drinks would have a much greater effect with much less effort. The problem is that the profit margins on carbonated flavored water are massive so the opposition to such change will be huge.

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> It seems like despite a lack of evidence, it would be very hard to ethically approve a randomised trial of teeth brushing over a long period.

This is the exact same argument that was used to evade studying the effects of low doses of aspirin on heart disease. Everyone “knew” it worked, so it was thought to be unethical to put people at risk of heart disease into a control group. Many millions of people spent money for years to consume a constant supply of aspirin.

When the question was finally studied, it all turned out to be nonsense. In fact, it turned out to increase death rates from higher cancer risk. All that money could have been spent on actually improving health.

https://utswmed.org/medblog/aspirin-heart-disease/

> When the question was finally studied, it all turned out to be nonsense.

That's certainly not the conclusion I came to at all from the article you linked. The main takeaway I got was that daily aspirin may not be warranted if you're not at high risk of heart disease (one reason earlier studies showed more conclusive benefits of aspirin is there were more smokers, i.e. more high risk people, back then).

So yes, it makes sense to look at risk/benefits for individual patients rather than "all old people get aspirin", but the idea that aspirin can protect against heart attacks is not nonsense.

I am pretty sure that low dose aspirin has some benefits for some people/conditions. At least I remember reading studies that suggest as much.

So naturally I was curious about it being “nonsense” for heart disease.

A quick skim of the article + a quick search shows it’s not as clear cut and conclusive as you suggest.

Interestingly, neither is the increased risk of cancer discussed in the article. Aspirin has been shown to have the opposite effect too.

I found it hard to glean what dosages where used in the studies mentioned in the article but the couple I saw were 100mgs per day. I didn’t see mention of if they were enteric coated or taken with meals.

In the US baby aspirin is 81mg and in the UK there are 75mg available. Both are enteric coated. In Australia it seems 100mg might be considered low dose and widely available.

It would be interesting to see more studies on this topic using lower dose, coated, aspirin taken with a meal. The US/UK low dose aspirin are 19-25% lower than at least a couple of dosages the studies mentioned. Those lower dosages may help mitigate bleeding risk.

Seeing as some of aspirins effects are longer lasting, perhaps alternative dosing schedules could also be looked at (every other day etc.) - this may further help mitigate the bleeding risk whilst still providing benefit.

The doses were different for legal reasons. Aspirin for children is unnecessarily risky in most cases but different countries set different cutoffs for restricted doses vs. unrestricted adult doses.

But ya, dosing is underrated. Something that's bad at X dose may be beneficial at 1/Yth the dose.

I agree. I’ve struggled with my teeth for years. Always hearing twice a day. But what I’ve learned is it does no good to wake up and brush your teeth and then have a coffee with sugar that sits on your teeth for several hours. I think one may need to brush many times a day depending on what you’re eating habits are. But I’ve also heard too much brushing can hurt as well so I still do a main brush morning and night but if I have something sugary or acidic I do a real quick brush. I truly believe for the best results you need to consider your teeth for the entire day and rinse them accordingly.

Hmm, you need to be careful -- AIUI if you have acidic foods then they soften the enamel, brushing immediately after can thus damage this enamel.

> it would be very hard to ethically approve a randomised trial of teeth brushing over a long period.

The ethics aren't too difficult because we don't have strong evidence one way or the other. I think a bigger issue would be blinding the study participants. The groups assigned to the higher frequency brushing may change other routines (e.g. diet).

> The problem is that the profit margins on carbonated flavored water

It could also be the strong acidity of a lot of drinks in general, even if we replace the carbonation/sugar with something else.

Importantly, phosphoric acid is the worst, carbonic acid is not as strong. I'm recently switching from sugared colas with phosphoric acid to naturally flavored carbonated water

anecdotal but i’ve visited third world countries where they don’t brush at all and some people had great teeth (others... nkt so much). not sure if it’s genetics or lack of sugary and acidic foods

They didn't brush their teeth, but were they chewing on small pieces of wood, or usong other traditional method of dental hygiene?

afaik they didnt do anything

Were you evaluating only color and straightness or were you looking for caries and periodontitis?

the first

How is carbonated water bad for your teeth?

Carbonated water is very mildly acidic.

Sodas (the sweetened ones), which I’m guessing are what GP is mostly referring to (what with the mention of sugar earlier in the paragraph) have sugar, which may encourage the growth of bacteria that are detrimental to teeth; and some of the flavorings are more acidic or react chemically with enamel to dissolve it.

The carbonation is one thing, but your saliva has lots of buffers to maintain pH.

There's usually a pile of acid added for "tartness" to sodas that lower pH, which overwhelms the buffers.

Often, it's phosphoric acid. Phosphoric acid will quickly react with any free calcium to form insoluble calcium phosphate which will mostly go right through you. So not only are you robbing your mouth of calcium you're also robbing the re-supply process.

Phosphoric acid is the bigger risk

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