What would you say to a mouth rinse that you use just once, but that protects you from tooth decay for the rest of your life? Okay. First, a quick lesson about tooth decay.
Most tooth decay is caused by a strain of bacteria called Streptococcus mutans. It consumes sugar on the surface of the teeth and converts it into lactic acid, which is what eats away tooth enamel, causing decay. A scientist, however, has discovered another bacteria in some people's mouths that kills this decay-causing strain. He's gone on to alter it so that it cannot produce any lactic acid of its own.
Scientists are divided on the fact that introducing an altered strain of bacteria into our bodies may be very dangerous. Some are wary; others say nature might eventually taken care of the bacteria on its own, suggesting that this rinse might simply be a way to speed up evolution. I should say, however, that the rinse is still in the testing phase.
In fact, it's been used on only three human subjects. And that brings me to another feature of the bacteria in this rinse. They need to be fed specific nutrients to remain alive and working. The nutrients take the form of a gum or mouthwash. The point of this quirk is that if you don't want these bacteria in your mouth, you simply don't feed them. Thus, you don't have to worry about catching the bacteria from kissing or sharing drinks with someone.