1) If it was an honest mistake, on your part, in not paying the dentist
 in the first place, as it sounds as though it was, then I imagine you
 should be able to explain that to your credit report people with some
 success, though it might take perseverence to clear all the records,
 especially if they've propagated. The effort of doing this could be
 greater than just paying the bill (which you might have to do anyway)
 and which payment could be a surer way of clearing your name.
2) If it wasn't an honest mistake, I wouldn't recommend trying to talk
 your way out, as you'll only do yourself more harm, rather pay the
 bill as soon as you can.
As for "making" them remove it, I am in no better position than you
 for this (in fact worse, as I don't know the details), though if you
 have no success under option 1 above, you may well be able to resort
 to an arbitrator, mediator, or watchdog body before an allout legal
 battle. Here in UK, we have quite a good Citizens Advice Bureau,
 which can help with this sort of situation for free - there MAY be
 an analogue in USA?