Charles Hardin, a dentist who worked in two Colorado prisons, including San Carlos Correctional Facility, a prison with a specialized population of inmates who have complex medical needs, says in a whistleblower lawsuit filed in Denver District Court that he was fired after he raised concerns that the state Department of Corrections’ default approach to dental treatment was to use mercury amalgam for dental procedures including fillings. The U.S. Food and Drug Administration in 2020 warned that mercury fillings posed a risk of harm to some patients.