Saying conditions at the Cook County Jail have improved, a federal judge has limited the reach of a class-action lawsuit that claims inmates are denied adequate dental care. In a written opinion, U.S. District Judge Joan H. Lefkow decertified one class of plaintiffs and reduced the number of members in the other. She took those actions because “some of the facts on which the court based its initial certification are no longer true,” Lefkow wrote. When the classes were certified, she wrote, the inmates …