I found out the hard way. I had coverage to receive 70% back. Went to my normal dentist and then to HBF and they gave me 30% back because it was not on their list.
I guess it stops dentists from rorting the system and charging the health insurers huge amounts.
Each health care provider has their own approved dentists, make sure you use one from their list. Your level of cover will decide upon how much the health care provider gives you back from the dentist bill.
I'm surprised the insurance companies are not funding them = being able to charge more for the premiums when people get infringements against their names.