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.
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.
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.