I have very strong (and ugly) teeth. The few "cavities" that I had, were actually made by dentists (they do that, y'know), and have resulted in a couple of crowns.
Otherwise, my teeth are great. I now have a dentist that doesn't make cavities, and she seems almost disappointed, when she checks me.
But gum care is every bit as important as tooth care (take it from me, you don't want a gum-scraping), and that is why I need to brush, floss, and mouthwash, twice a day.
I _do_ have to brush my teeth etc... though, because i tend to have a lot of plaque if i don't.
Apparently either it is cavities, or plaque. You must take care of your teeth!