SANTA CLARA - The 49ers brought in plenty of defensive reinforcements this offseason to bolster a starting rotation that has played nearly every snap the past two seasons.
But defensive coordinator Vic Fangio isn't signing off on a plan for more platooning just yet.
"It's a possibility, but those (new) guys have to earn the right to be allowed to be put in the game," Fangio said. "You just don't platoon guys for the sake of platooning. You don't want to go down in the quality of your play just for the sake of playing guys."
One of the issues is that neither of the defensive linemen the 49ers drafted in April - second-round pick Tank Carradine and fifth-round pick Quinton Dial - has practiced yet. Carradine is coming off an ACL injury suffered late in the college season, while Dial is dealing with a toe injury.
Fangio said he didn't think either rookie would be available for the start of next month's training camp.
The prognosis is better for perhaps the 49ers' most pivotal player on defense, right defensive end Justin Smith.
Smith, 33, partially tore his left triceps tendon in Week 15 last season and played with the injury during the postseason. Following surgery in February, Smith is back in the weight room, is bench-pressing 350 pounds and says he's on track to be ready for training camp in late July.
If the 49ers had a game today?
"Oh, yeah, I'd be good to go," Smith said Wednesday.
Until the injury, Smith had played nearly every defensive snap during the regular season, as had fellow defensive end Ray McDonald and outside linebackers Aldon Smith and Ahmad Brooks.
Like Justin Smith, Aldon Smith and Brooks have missed all of the spring drills as they recover from shoulder injuries suffered last season.
There's little question the 49ers' defense wore down at the end of the season and in the playoffs. They gave up 520 yards to the Patriots in Week 15 and 477 yards to the Falcons in the NFC Championship Game, two of their most porous performances of the season. They allowed an average of 24.8 points on the season but 30 points per contest from Week 15 through the Super Bowl.
Asked if he would benefit from more rest during the season, Justin Smith said: "There are definitely guys in there worthy of some reps. Anytime you have that situation, you look into it."
As of now, the top two backups at defensive end are Will Tukuafu and Demarcus Dobbs.
Last year at this time, Smith, who turns 34 in September, said he figured he had three or four more years left in the NFL, and he noted his window for winning a Super Bowl is limited.
He said he's taking the same approach in 2013.
"It's a lot like the year before, getting to the NFC Championship Game," Smith said. "This one, we were right there. It's really disappointing. You can either let that tear you down, mentally, as a team, or build you up. I think we're taking the 'build-you-up' approach, and we're realizing what needs to be done to get there. Now we know even more what it takes to win."
Smith also is nearing the end of the six-year, $45 million deal he signed with the 49ers in 2008. He is scheduled to be a free agent in March but insists he's not thinking beyond this season.
"I'm thinking about 2013 and 2013 only," he said. "At this point in my career, nothing's a given, nothing's a guarantee. They (the NFL) don't like old guys, anyway, for football. I'm going to enjoy this year and do the best I can this year, and hopefully it's enough for us and the team and we get it done."