Dentist Question

My husband went to a new dentist today and they seemed very nice. They did a few fillings and said he needs scaling but he needs a cleaning first. All good. So the lady proceeds to say that sometimes insurance companies will say that they will cover a cleaning and then won't so we would be required to put down $139 and if our insurance covered it then they would reimburse us $104. I found this a bit odd for a couple of reasons. One, we have Medicaid at the moment so anything they cover is of no cost. Why would we end up paying $35? Two, I called the insurance company the other day and the first thing they said was that cleanings are covered 100%. Any insurance that I've ever had, has covered cleanings. Now I don't have a problem if it legitely ends up costing $35 because thats not bad. I just want to make sure that we are not being taken advantage of because a lot of the dental offices in our area are not the most honest. If anybody has any experience in this, please give me your input because I just feel off about the whole situation. Thank you!