I got Invisalign a month ago and I'm on aligners #3. I just started noticing that between my teeth are starting to turn brown. First it was just one tooth up top and now my bottom teeth are turning brown between the teeth. I brush, use mouthwash and floss after everytime I eat, which is about 4 times a day. What could be causing my teeth to turn brown between my teeth? Could I be over brushing, mouthwash and flossing?