worker's comp hasn't paid my dental bill even though it was preauthorized. Is it legal for the dentist to send this to collections? Do I have to pay?

I have been contacted by collections and told the dental office is willing to settle with me for a bill that was pre-authorized. The dental office has been fighting with Maryland worker's comp for over a year to get this bill paid and they are constantly getting the runaround. Now they say that they have given up on worker's comp and I have to pay the $1300 bill.