Is there any internet sites available to check a dentist back history, to find out if he might have had bad practice issues in the past

It all depends on where you live. You can try googling the department of health for your State (if you are in the U.S.). Many Health Departments have a License Verification link where, at least in my state, you can check if the dentist is licensed and if he has ever lost any malpractice suits.

Good luck.