A man who alleges he was denied prompt treatment for severe toothaches and other dental problems while being held in the Cook County Jail got the go-ahead to pursue his lawsuit as a class action.In a written opinion this week, U.S. District Judge Matthew F. Kennelly certified a class of plaintiffs in a suit Demetrius Whitney filed against Sheriff Thomas J. Dart and other defendants under the Eighth Amendment.The class includes current and former inmates who submitted urgent requests to be treated at the dental clinic at …