The Steelers on Sunday face a San Francisco defense that has endured several personnel changes since the teams' last meeting four seasons ago, a 20-3 49ers victory at Candlestick Park.


With the exception of linebackers NaVorro Bowman and Ahmad Brooks, the 49ers have overhauled their defense. The cornerstones of the 2011 unit — linebacker Patrick Willis and defensive end Justin Smith — are gone, as is coordinator Vic Fangio.


Despite the changes, the defensive schemes and philosophy remain the same...........