Think of these L.E.D. teeth as throwies for the mouth. As written in the NYTimes:

The LED smiles can easily be affixed to your teeth and glow different colors while you smile. The colors can be changed wirelessly through a computer interface. Of course they work best in the dark.

The video of Motoi Ishibashi, one of the designers, is highly reminiscent of the guy that used his face as a musical stimulator.

View more L.E.D. smiles here.