Do I have to pay dentist for something my insurance denied?

So my friend went to the dentist for a cleaning and was told she needed a crown. She agreed and got it. She then got a notice from her dental insurance saying the procedure was denied bc to be approved, there needed to be evidence that a filling wouldn't fix the problem and it would get worse...more technical than that, but close enough. She called the dentist and they said she had to pay the close to 500 dollar bill. Her insurance told her that the dentist should have gotten pre-approved for the procedure and she didn't have to pay. The dentist is telling her she owes the money and in thirty more days, they will turn it over to collection. Who is right, does she have to pay it, or how can she fight it? If it helps, it's United Concordia, military dental.
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You have a contract with the insurance company. Your dentist has nothing to do with their polices. He was doing what was best for you and what your tooth needed. The insurance company is just trying to get out of paying the claim so as to add to their profit. This is a game they play. There is no legal requirement for a dentist to need approval of an insurance company to do any procedure. The people in the insurance company are not even dentists and wouldn't know how to look at an x-ray. Who do you want telling you what treatment you should have? Your gripe should be with the insurance company rat finks and not with the dentist. You will need to pay the dentist and fight with them.
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