Wear and tear on players is inevitable over the course of a long NFL season, and it was one reason cited for the 49ers' drop-off on defense at the end of the regular season and in the postseason in 2012-13.Analysts particularly pointed to San Francisco's defensive line, where Ray McDonald and Justin Smith were almost always on the field. In fact, over the 2011 and 2012 seasons, 3-4 ends McDonald (2,165) and Smith (2,141) ranked third and fourth in the NFL among defensive linemen in number of snaps played, according to ESPN. McDonald was one of only three defensive linemen in the league last season to play at least 90 percent of his unit's snaps.So, this offseason, the 49ers were intent on bringing in players who could add depth along the defensive front. Nose tackle Isaac Sopoaga and key reserve Ricky Jean Francois left the Niners in free agency, but veteran Glenn Dorsey was added from the Chiefs and San Francisco brought in defensive linemen Tank Carradine and Quinton Dial and pass rusher Corey Lemonier in the draft. Plus, former backup Ian Williams has been given a chance to contribute, and could win a starting spot at nose tackle. With Dorsey and Williams, plus Carradine,...