DENVER (CBS4) – A former employee may have launched the state investigation into Dr. Stephen Stein and a practice of re-using needles and syringes.

The state health department has sent letters to 8,000 patients, advising them to get tested for HIV and hepatitis. So far no cases have been linked to Stein’s practice.

He practiced in Denver and Highlands Ranch but gave up his license in June, 2011. That was apparently after a woman who had worked for Stein contacted CBS4. She claimed Stein was ordering drugs in the names of patients and she questioned the practice.

The former employee also indicated she wanted to let the state known about her concerns.

The dental board’s investigation of Stein led to the agreement where he stopped practicing. In the course of that probe, the state discovered the practice of re-using needles and syringes. Investigators informed the state health department about that practice in April and warning letters went out the second week of July.

The Denver Police Department is also investigating Stein. The dentist’s attorney says he is cooperating.