OK…I’m back. So, what causes a cavity if neither bugs nor sugar have, in and of themselves, the ability to do so? What about brushing (or the lack thereof)? Does the lack of brushing cause a cavity? No. In and of itself, a "toothbrush-allergy" lacks the ability to create a hole in a tooth. Does anything, “in and of itself” cause a cavity? Yes. ACID does. "The Joker" can tell you all about the destructive nature of acid.
Where does the acid in our mouth come from? That's where it gets interesting. When we explain this part of the story to kids, their eyes get really big. Stay tuned to see why.