Please explain who do i complain to about bad dental service?

The dentist: If you had a problem with the treatment outcome, you need to discuss this with the dentist so that s/he can try to make things right. Often it is a miscommunication and things can easily be corrected. If it is beyond that point, then contact your local dental society. They will usually intervene and mediate any disputes, within reason.

To the dentist: Sometimes you might feel something was done wrong, but find out from the dentist first and get things straightned out.

Discuss your problem with your local dental society and if legitimate, they will pursue the problem for you.