Which toothpaste has the most fluoride?

ACT fluoride rinse might be what you are looking for. I've used it on/off and found it worked well with preventing cavities than brushing multiple times, using different toothpastes, etc. You can also try brushing with Sensodyne brand toothpaste. I used it for sensitivity on my teeth, but its written on the box that it has "maximum strength with fluoride" and is good for cavity prevention. Hope this helps. GL!

According to http://en.wikipedia.org/wiki/Toothpaste#Fluorides, you might try buying your toothpaste in the UK.

I can't imagine that 1/100% difference is going to matter to your teeth at all. If you are looking to maximize the amount of fluoride you get, brushing more often with a cheap toothpaste will probably be more cost effective, and more effective for your teeth, than buying a premium toothpaste.

My guess is, as others and Wikipedia imply, that these pastes all have about what is considered the "limit" for US toothpastes. As you said, you can get higher ones with a prescription, but I'm guessing these limits are there to best prevent as many cases of dental fluorosis as can be. (No toothpaste manufacturer wants to be sued for that!) Also, the limits in rinses seem to be different. ACT claims they have "http://www.actfluoride.com/actfluoriderinse.html" and their rinses just have 0.02% w/v fluoride ion. My guess is that without all the sand, surfactants, &c. in toothpaste, the rinses can use much less sodium fluoride.

Lately I'm a fan of http://www.amazon.com/exec/obidos/ASIN/B0037LGHA6/metafilter-20/ref=nosim/, which is 1.15% Sodium Fluoride. The regular AIM is Sodium Monofluorophosphate (0.8%). Interestingly AIM as a brand doesn't have ADA approval seals on any of their products. I'm not really sure what's up with that.

As crunchland said the floride content is probably going to be the best in the uk. I had a dentist tell me( a friend not professionally) that anything under 1400ppm is a waste. Since finding this out I have been checking toothpaste, and within the same product(though different sizes) seen staggering differences in amounts. This is probably the only conspiracy I will get involved in, I have noticed more sensitive teeth for lower floride contents. The tooth paste manufacturers are out to get me!!!!! I could probably ship you a taster if you are really bothered.

How do you find the ppm with the w/v percentage?

weight-per-unit-volume to ppm isn't simple because you need to know the density of the material. Thankfully, someone appears to have prepared a little chart for the common fluoride donors at the http://en.wikipedia.org/wiki/Fluoride_therapy page.

My impression is that the fluoride content in toothpaste is not itself going to be that important, especially if you're drinking fluoridated water1 in the first place. I had a friend who brushed with water only, due to some sort of allergic reaction to toothpaste, and according to him (relaying his dentist's advice) it was more important to brush at all (and on the recommended schedule) than it was to brush with toothpaste. Here's what the http://www.cdc.gov/fluoridation/other.htm#5. If you've discussed your needs with your dentist, s/he may recommend an additional product or tool, such as a fluoride rinse or interdental brushing. 1That said, the EPA is http://directorsblog.health.azdhs.gov/?tag=fluoride-toothpaste in drinking water, due to toxicity hazards.