S. mutans attach to the surface of the tooth. When fermentable carbohydrates, like soda, candy, etc., are introduced into the mouth, S. mutans processes them and make acid.
This acid is what eats away at the surface of the teeth, causing dental decay.
Fluoride, regular cleanings, and sealants are some ways to keep your teeth safe from S. mutans and other cavity forming bacteria.
However once the area is cavitated (there is a hole) you need to have it drilled out and filled by a professional like Dr. Linhart, or myself.
What you fill the cavity preparation with, tooth-colored composite or silver amalgam, is a story for another day…