That's what I learned at the dentist this afternoon. That, and I have a cavity.
See, since I haven't been flossing for the last three months lately, my gums were really bleeding while she was cleaning. So the dentist mentioned that birth control can do that to you. (Isn't every 20something woman she sees on the pill? No?!) Of course I had to ask why, and it turns out your gums bleed more when your levels of progesterone and estrogen change. Of course, this happens naturally when you're on your period, pregnant, and going through menopause (not all simultaneously, obviously!). That's not a big deal because it's a relatively short period of time.
The step she didn't take was to say that when you are on the pill for a long period of time, it might become a big deal. This is a single woman who lives in NYC, after all. There's no way she's saying that. And perhaps it's not true - I'm not a dentist, so I don't know. Just thought I'd throw it out there!