The recommendation to floss was removed from the federal dietary guidelines in January after 25 years, due to a lack of evidence to back up the suggestion. Jeff Donn, the Associated Press reporter who broke the story in August, found the first thread to pull after a routine meeting with his son’s orthodontist when the doctor asked if Donn wanted a good tip. This week on “Take Care,” Donn, a 30-year staffer for AP and a 2012 finalist for the Pulitzer Prize for national reporting, shares his story