Bacteria!

There are millions of different bacteria, and many different kinds live in our mouths.  A handful of species are known to cause cavities.  Recent research into possibly eliminating only the harmful bacteria produced the future possibility of a mouthwash that keeps us from getting cavities.  Here is a link to a summary article:  http://www.procprblog.com/ucla-develops-innovative-anti-bacterial-mouthwash-to-wipe-out-tooth-decay .

It seems that if the mouthwash proves safe, we will have a powerful tool to prevent oral health problems.