Exercise is one of the best things you can do for your body — it strengthens your heart, improves your mood, and boosts your overall health. But while hitting the gym or the running trail can do wonders for your fitness, it can also have some surprising downsides for your smile. Believe it or not, certain exercise habits can put your teeth and gums at risk. Here are 5 ways exercise can harm your oral health and what you can do to protect your winning smile while staying active.