I have crowded top teeth. I have a good oral hygiene. I brush and rinse twice a day and floss before going to bed. There are grayish brown spots between my crowded teeth. They are quite visible when I smile. Would my teeth be rotting or are these tartar build-up? They won’t go away no matter how I brush or floss around them. Does anyone have any ideas what could these be and what should I do to get rid of them? I would be very thankful for any advice.