FLOWERY BRANCH — Atlanta Falcons coach Mike Smith is having a tough time keeping his starting middle linebacker healthy. After losing Curtis Lofton to free agency in the spring, the Falcons signed Lofa Tatupu to replace him, but a torn pectoral muscle ended his season before the start of training camp. Now Atlanta must temporarily replace second-year linebacker Akeem Dent, who sustained a concussion in the 31-17 loss to Baltimore and will miss next week's exhibition against Cincinnati.