In The Master, In order to achieve the effect of clenching his mouth and talking out of one side, Joaquin Phoenix had his dentist attach metal plates to his teeth with rubber bands to hold them shut. The rubber bands weren’t strong enough to hold his mouth shut, so he removed them. But the metal plates, complete with screws that slightly cut up the inside of his cheek, were enough of a constant reminder that it allowed him to play that aspect of the character (x).
The Master (2012) Dir. Paul Thomas Anderson