The problem with the replacement of copper pennies by aluminum pennies.
D000535:Aluminum; D001466:Barium Sulfate; D002675:Child, Preschool; D003300:Copper; D004724:Endoscopy; D004947:Esophagus / Q000000981:diagnostic imaging / Q000601:surgery; D005547:Foreign Bodies / Q000000981:diagnostic imaging* / Q000601:surgery; D006077:Government Agencies; D006801:Humans; D007830:Larynx / Q000000981:diagnostic imaging / Q000601:surgery; D007878:Legislation as Topic; D011859:Radiography; D014132:Trachea / Q000000981:diagnostic imaging / Q000601:surgery; D014481:United States
D001466:Barium Sulfate; D003300:Copper; D000535:Aluminum