What can I do about this dental insurance claim?

Recently I needed to have a dental procedure done, and the dentist’s office said they would check with my dental insurance provider (Delta Dental) to see if it would be covered. The dentist explicitly told me it would be covered, so I went ahead with the procedure (I could not really afford it otherwise). Now that the procedure has been done, the dentist sent me a bill and informed me that the insurance company denied the claim and I must pay the full amount.

I talked to the secretary at the dentist’s office this morning and she told me that ultimately it’s my responsibility to know what’s covered and that they just do the best they can. She was pretty unsympathetic.

However, the Delta Dental website says, “Dentists who accept Delta Dental will file claims for you. You only need to file a claim when visiting a non-Delta Dental dentist.” I don’t know what I could’ve done since it’s the dentist’s responsibility to file the claim, not mine. What are my options here? Have any of you ever been in a similar situation?