Minors, vulnerable parties, and intoxicated people are unable to sign contracts. That a dentist would incapacitate you and then have you sign would be an instant rejection in court.

It would not be just unethical, it would be illegal.

This is how every single such no interest payment plan works. It was written on the paperwork you sign and likely every monthly statement. Rather than read, you’re complaining that it was not read to you.

You have my pity but you are 100% in the wrong.