According to Merriam-Webster, biofilm is defined as a thin usually resistant layer of microorganisms (such as bacteria) that form on and coat various surfaces. Environmental biofilms are found on the mountain stream rock beds, the dog’s water bowl, etc.. Oral biofilms are the slimy layer on retainers and night guards. They are present in the sulcus and depending on the composition of the biofilm can be very pathogenic. Biofilms are constantly responding to their environment and evolving. ...