What should you do when dentist removed back molar gold crown and replaced with resin without permission and denies it?

There are two issues here i fact. The first is your claim that the dentist performed a treatment without your permission. If this is true then your dentist may be liable because he is expected to have you sign an informed consent prior to starting any treatment. Are you sure you didn't sign anything. The dentist or one of his staff usually asks you to sign this together with the medical questionaire and patient record that your are asked to accomplish at your first visit to the clinic.

The second issue is of course the gold restoration as a precious metal. Was the gold given back to you? As a routine procedure, a dentist will have a record of your teeth prior to treament. On the pre-treament record it should show the status of your oral cavity including the presence of restorations, decayed teeth, dentures etc. It should also indicate missing or extracted teeth. In the same record, he is also supposed to indicate all dental work that he has done on you. If your dentist has indeed done this that constitutes unprofessional and unethical conduct. You can of course take the dentist to court. I admit that this is not an easy process for you or the dentist. The courts can subpeona these document if need be. You can try also reporting the incident to the national dental association of your country as see what they can do.