Get the Popular Science daily newsletter💡 Breakthroughs, discoveries, and DIY tips sent six days a week. “Sugar rots your teeth!” You’ve likely heard those words, in some shape or form, coming from a parent, grandparent, teacher, or TV show. In school, you might have even conducted a classic experiment: putting an egg into a cup of soda to see how the shell softens and becomes flabby after a few days. That, the lesson implies, is what sugary soda does to your teeth. However, sugar is not the direct cause of cavities. Nor is it a corrosive substance, like the common classroom experiment implies: In fact, it’s the tangy acid in the soda that softens the shell, not the sugar. Sugar, however, is a great energy source for the bacteria living in your mouth that can cause tooth decay, says Dr. Diana Nguyen , the chief of General Clinical Dentistry and associate professor at University of California, San Francisco School of Dentistry. But should we really only blame sugar for cavities?…