What should I do about this dentist?

So, I got dental implant crowns put on my teeth about a year ago. I asked the dentist's office to bill my insurance company, but they insisted that my insurance wouldn't cover the dental implants because they are considered cosmetic. I argued with them about it, until they said that I had to pay for my teeth w/my own money, and they would file with my insurance and reimburse me if my insurance did end up paying. So they filed, and of course my insurance company did in fact cover a portion of the cost of the procedure. My insurance sent me a letter back in April saying that they had sent a $600 check to the dentist. I have yet to receive any reimbursment check from the dentist. I called them today, and they said they would send me a check at the end of the month. I have a feeling that I won't be getting anything from anytime soon. So, what should I do if I don't recieve any check by the end of the month?