If you don’t brush regularly, you probably have a biofilm of bacteria 300 to 500 cells thick on the surface of your teeth (don’t worry, it’s less than it sounds).

The dominant species in this dental plaque are Streptococcus sanguis and S. mutans. Even if you brush diligently, these bacteria will still be there: They arrive soon after your teeth do and stay until they fall out. The bacteria ferment sugars and secrete gluey polymers that form the basis of plaque.