Is it legal for a dental assistant file and cement my final crown in NC?

I had few crowns done last year with this new dentist, and when my final crowns have arrived they were file and cemented by the dental assistant, in fact on that appointment I have not even seen the dentist. The assistant was ok but she file the Emax crown for tooth #9 in an angle and I was left like that. This year i want to replace 4 front teeth with Emax to match including redone #9 but i don't know weather i can refuse to have them put in by the dental assistant.