Shady AF.  I'm going to add this to the list of times where actually HAVING health coverage (or dental in this case) actually results in shit costing more.

When you get a statement of benefits that indicates several hundred dollars as "This provider has agreed to not bill you for the difference between the PROVIDER'S CHARGE and the ALLOWANCE for this service" but they sure as hell DID charge you that several hundred dollars you would think that the insurance company would want to know.

Nope, instead they said "that is between you and your dentist".  Seems a little fraudy to me.