non transparent dental charge

My wife has a full dental coverage for routine tooth-cleaning. When we went

to Holbrook Dental we were told by the

receptionist everything for the visit will be covered. Then during the cleaning, the dentist changed to another method of cleaning and told us about the method of cleaning and he did not give us any hint that this cleaning is a non- routine cleaning, more expensive and we need to pay it from our own pocket. My wife did not even think about that this may not be covered by insurance. How would any body know a little change could completely change the coverage? We had too many experiences with dentists. But we still fell into the trap this time, even after we asked about the coverage before the visit. When we asked Holbrook Dental Associates about the charge, our response is that they are not responsible in telling us anything about our insurance before the treatment, because he has no way to know it. So I suggest people who are not experts in dental treatment and insurance do not go there. Because you will be responsible for anything they do to you, and you have to ask any details about the treatments and dental material, etc, any of which could easily go up to more than several hundreds.