Tuesday, February 14, 2006

Here's What I Don't Get:

How in the world does toothpaste work?

The typical tube of toothpaste weighs in at roughly 6.4 ounces. That's 181 grams (If you've got the larger 8 ounce tube, you're sitting pretty at 226 grams, but for the sake of this exercise we'll stick with the standard size tube).

The active ingredient is sodium fluoride. In a standard tube that active ingredient composes about .243% of the total mixture.

That means for every 100 grams of toothpaste there is .243 grams of sodium fluoride. So to figure out how many grams of active ingredient are in a tube of toothpaste we need to complete the ratio. Generously rounding .243 to .25, and 181 grams to 200, we can see that in a tube of toothpaste there is approximately half a gram of active ingredient.

Now I don't know about you, but I'd guestimate that my wife and I get about a good 100 uses out of a tube. (These guys figured out that a 6 ounce tube would get you about 113 uses, so I'm pretty sure that's a decent estimate). Assuming for a minute that the active ingredient is distributed throughout the tube in a perfectly even fashion, that means that in each of 100 brushes you should get .005 grams of sodium fluoride on your teeth.

Maybe it's just me, but that sure as heck doesn't seem like it'd be enough to accomplish anything. Even if you brush in a ridiculously thorough manner, I can't imagine you'd touch that tiny bit of sodium fluoride to all of your teeth. And considering that the active ingredient probably isn't distributed perfectly throughout the tube, from time to time you're probably brushing your teeth with completely non-active ("inert") ingredients.

So seriously, how does toothpaste work? I don't get it.

Something better than nothing


Anonymous said...

Marie Curie said the same thing about radiation.

joel. said...

I'd wager a bet that the active ingredient IS uniform throughout the tube. While we are talking about fractions of a fraction of a gram, we're also working on a microscopic level. It's not as though the tube has a dozen grains of sodium flouride floating around in the inert paste. There are billions of billions of molecules spread throughout and suspended in the solution. I think your teeth are getting plenty of NaF per brushing.

Also, just because the sodium fluoride is the only "active" ingredient, that doesn't mean the other ingredients are superfluous to the effectiveness of the toothpaste. Additional substances such as baking soda also play a role in the cleaning procedure. Even the mere act of scrubbing your teeth with the rigid bristles and foaming paste helps, NaF or not.

FWIW, I just did a little (and I mean very little) silly research on one particular brand of toothpaste and came across this PDF. There a page or two on abrasiveness and it seems as though some toothpastes are abrasive enough to actually do harm instead of good. Whoops.

(Before you ridicule me for commenting here and not on the morality post, remember that you posted on dental care--something I actually know a reasonable amount about.)

Matthew B. Novak said...

For the record, I didn't say that toothpaste doesn't work, only that I didn't understand how it does.

And Joel, I think you've helped clear it up for me. Though I'm still skeptical that the sodium flouride gets everywhere, all the time. It seems like there would be more and less effective brushings.

Also, what does flouride do for teeth? I'm look at you for this one, Gina.

Jeff said...

Even more mind-boggling is this - the fluoridation of water (a Communist plot!) is done to the tune of 1 ppm fluoride. That's 1g fluoride per 1000000g water.

And the amount of benzene your body can take without getting sick? Also 1g per million g of air.

Chemistry functions on very small levels. Tomorrow I get to play with DNA that weighs 7 nanograms. Whee.

the marvelous patric said...


Anonymous said...

For the microscopically challenged.
What you seem to think is a very small 0.005 grams of NaF equates to approximately 7.17x10^19 particles/atoms of NaF. If that doesn't do it for you that equates to 71,700,000,000,000,000,000. In other words it is one heck of a lot of active ingredient. So I would argue you are getting plenty of your active ingredient.

Gina said...

We haven't really gotten to how toothpaste and fluoride work yet. All I know is that it is a law to have flouridated water. I'm sure we've talked about it somewhere but I just got home from school and am too lazy to look it up.

I do know why whitening toothpastes whiten, its due to their abrasiveness.

I think Joel was right on when he said that NaF is not necessarily the most important part of toothpaste, that the actual act of brushing (and then flossing!!!) is what really helps your teeth and gums.