Locate the licensing board for dentists in your state. Each state determines what qualifications a dentist must have in order to secure and maintain a dentistry license. Most states have a website that allows you to search a dentist by name to ensure that he has a valid license to practice in your state.
Search for disciplinary complaints. When someone is unhappy with the services of a dentist, he can file a complaint with the disciplinary board that oversees licensed dentists for your state. The same board that licenses dentists generally accepts and investigates formal complaints. You should be able to search online or by calling the board.
Investigate county court records for civil malpractice cases filed against the dentist. Not all complaints rise to the level required to file a malpractice lawsuit, but those that do will be public record in the county where they are filed. County records can frequently be searched by name online or in person at the clerk's office. Look for lawsuits where the dentist was the defendant.
Pay for a personal background report. Many companies do background reports on licensed professionals for a fee. If you do not have the time to do the legwork yourself, you can pay to have your dentist's background -- including any lawsuits -- investigated.