How do I get rid of these brown lines between my teeth?!

For a few months now, I've had brown lines between my front teeth (up and down). I don't think my food and hygiene habits have changed, but I guess american food may contain more sugar or something (moved here last summer). There doesn't appear to be any real problem with my teeth, but i think cavities can take years to develop? However, it doesn't look very nice. I can't remove it by flossing or picking at it with my nails. I've planned on going to the dentist pretty soon, so don't just tell me to go and get it examined. Any ideas about it?