Bob brushes more carefully with NEW STYLE BRUSH than he does with OLD STYLE BRUSH, thus leading people to think that the new brush is better. When actually, it isn't, because it misses the gum line and doesn't help prevent gum disease. Thus, the population using the new brush has more fillings, extractions, deaths from surgery, and deaths from heart disease associated with gum disease.

There's a reason science is rigorous.

> I'm not certain why you believe that you need to run double blind clinical trials on a tooth brush

Double blind means that neither the researcher nor the subject knows which device the subject got.

I don't think that this is possible (he said, with some understatement) when comparing a standard toothbrush to a bristly mouth guard thing.

Yeah, you don't need a double blind study here... Just measure the plaque levels before and after usage.

As long as the plaque reductions are comparable, as well as the absolute final values, you're golden.

Looks like the savings is about 6 days over 5 years (http://xkcd.com/1205/). At a cost of $900 that's not a bad return on investment.

One important aspect of tooth brushing is gum stimulation, which is harder to measure than plaque removal.