5 year old is getting dental crowns on front teeth?

in a couple weeks my son is going to be having some dental work done, including caps on a couple of his front teeth. the dentist i took him to was very set on all of the caps being metal because they are "easier". i refused the metal ones for the front teeth and opted for porcelain face caps and he was trying to talk me out of it. i still have this feeling when he wakes up that he will have metal instead of the porcelain fronts. is there anything i can do to ensure that this does not happen? like maybe get something in writing before the surgery, also if it does happen, can i take legal action? this dentist is a bit pompous and is the only exclusively pediatric dentist in town