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Comment by deltaqueue | Hacker News Reader

I wish he would have provided more explanation behind the dentist's algorithm. Here's an actual study measuring enamel loss, which seems much more definitive:

http://faculty.philau.edu/ashleyj/General%20Dentistry%20Arti...

Perhaps the most important snippet:

Regression analysis indicated no correlation between enamel dissolution and beverage pH (r = 0.477, p > 0.05); in addition, the enamel dissolution showed no difference (p > 0.05) between the regular and diet versions of cola and non-cola beverages from the same manufacturer (Fig. 2 and 3). It was noted that the enamel dissolution was similar for all cola drinks over the 14-day test period (approximately 3.0 mg/cm2).

And again:

The data suggest that enamel aggressivity is determined by beverage composition rather than by beverage pH.

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Or how about experimental science? Get some human teeth (probably not difficult or expensive for a dentist), weigh them, plunk them in each liquid, let them sit for a week, see which ones lost the most mass.

Obviously scientific rigor would require several experiments to smooth out the variances in individual tooth quality and original composition, but it seems like that would come to a more definitive conclusion.

I think the presence of saliva has a major effect on inhibiting tooth decay. I'm not sure how applicable in vitro experiments would be.

It would give us a new hypothesis to test, and if it turns out to be wrong, it would tell us a lot about saliva, don't you think?

Exactly, hence the problem with allowing babies to sleep with a bottle. It's not the milk in the bottle that does the harm, it's the uneven saliva exposure in the mouth.

In general, people with good salivary coverage get less tooth decay. People with dry mouths, for whatever reason, get more. This isn't exactly an avant garde research topic.

While the dentist has impeccable credentials, she seems too reliant on anecdotes and personal observations, and insufficiently rigorous (to put it mildly) in justifying the mathematical model she proposes. The reasoning in this article is a little better than the old science-fair standby of dropping a tooth in a glass of Coke and gasping with horror when it's gone a week later, but not much.

Teeth continuously remineralize in living humans, so this experiment wouldn't tell us anything useful.

Do they? Even so, they will remineralize at the same rate regardless of the substance which dissolved them in the first place, right? (Ignoring, of course, that the ongoing presence of bacteria feeding on sugars may counteract the remineralization). The experiment would still demonstrate which substance destroys teeth the fastest.

Those bacteria you're ignoring are likely to be the key factor in this whole business, so it seems like a highly incorrect simplification.

A human tooth submerged in Pepsi will actually dissolve completely in less than a week.

Is that true? I remember Mythbusters disproving the myth that it would dissolve a tooth overnight.

Perhaps a week is too much time.

http://www.snopes.com/cokelore/tooth.asp suggests that submerging teeth in any acidic substance (e.g. orange juice) will soften and eventually dissolve them. Since this does not adequately replicate conditions in the mouth, it would not be useful to determine how such substances affect enamel.

I don't see how "not adequately replicating mouth conditions" leads to "would not be useful to determine effect on enamel".

Yes, there will be significant differences between drinking Coke and soaking a tooth in Coke overnight. But that doesn't mean it won't provide a useful basis for comparison! Possibly even more useful than the arbitrary formula the author and dentist in the article came up with.

>But that doesn't mean it won't provide a useful basis for comparison!

Why bother? There are plenty of people out there who've been drinking coke for decades. All you need to do is compare their dental health to people who don't.

What useful basis does it provide?

I agree with your sentiment, but a large factor in tooth decay is bacteria that live in your mouth: http://en.wikipedia.org/wiki/Dental_caries

This seems like what the article gets wrong as well. What you drink and eat impacts the environment in your mouth where bacteria flourish which in turn impacts tooth decay. There just isn't such a direct cause/effect relationship between pH/sugar and tooth decay, although they are certainly strongly correlated.

As a result, I'd take this article as a loose framework rather than a true scientific ranking.

p>0.05 does not mean that a correlation has been disproven, just that the authors are unable to reject the null hypothesis (potentially due to lack of statistical power).

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