First of all, the bad news: Neither brushing nor flossing has a significant, scientifically proven effect on cavity prevention, says Philippe Hujoel, a dentist and professor of oral health at the University of Washington School of Dentistry. (That said, the fluoride inside some toothpastes does strengthen your teeth.) Instead, the best way to prevent cavities is to avoid, as much as possible, sugar and other simple carbohydrates. However, that doesn't necessarily mean you should stop brushing and flossing altogether. Both activities keep your teeth clean and aesthetically pleasing—and remove any rogue broccoli or other food particles stuck between your teeth.