Is it illegal for a dentist to not allow parents into the room where their child is getting dental work?

To make a very very very long story as short as possible..My daughters dad took our daughter to the dentist where they told him she had 2 cavities and needed to get some dental work done. Basically he said the dentist told him he wasn't allowed in the room because he was going to make her nervous. He said he wasn't ok with it but went to the lobby anyways. After being in the lobby for 10 minutes he said he "needed" to use the restroom and instead of going to the restroom went to check up on her. He said the curtains were closed (they don't have doors) and that he slightly opened it and saw my daughter had tears, had her hands & legs restrained and that he heard the dental assistant (a guy) telling her you better stop moving or we're going to give you a bigger injection so you can fall asleep and when you wake up it's going to hurt even more. He said when the dentist saw him peeking that he got up and told him to wait in the lobby that he wasn't allowed and my daughters dad said he said no, I will not wait outside, untie her, finish doing what you're doing and I will never come back here and proceeded to tell the dental assistant who the hell he thought he was to scare her that way. So he said again the dentist insisted in him waiting outside, and my daughters dad told him I'll be damned to leave my daughter in a room with 2 men. Which I know was totally uncalled but then again the world is a crazy place. Anywho, he said there was a back and forth of words and that at the end the dentist said he wasn't going to work on her cativities, to take her somewhere else. Fortunately, he had just numbed her and hadn't drilled yet. I called our insurance but it's already closed. I called the dental office but all the receptionist said was that we would be hearing from the dentists lawyer, that they were going to sue my daughters dad for defamation of character. I completely understand where the dentist is coming from (I know my daughters dad can be pretty nasty) but then again isn't it illegal to keep a parent out of the room where their child is getting any kind of medical procedure done?
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I don't think it's illegal. I think it's up to the dentist to say. But, her father had every right to pull her out of there. He doesn't have to force his child to be anywhere. She can get her teeth fixed somewhere else. I doubt they have a case or will even push it. They probably felt threatened thinking he might sue. I would just hope and pray it all blows over. Your daughter on the other hand is going to be terrified to go to the dentist now. How old is she? Can you take her to a pediatric dentist?
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