Dempster started against the Reds on Thursday on his 35th birthday. He had been sidelined with a strained right quad, last pitching on April 17 against the Marlins. Wood, 34, has not pitched since April 13 because of right shoulder fatigue. He was 0-1 with an 11.57 ERA in four relief appearances this season.
Maine, 27, posted a 1.59 ERA in five relief appearances after he was recalled April 20. His departure leaves the Cubs with one lefty, James Russell, in the bullpen.
"[Maine] did a good job while he was here, a really good job, and it's very nice to have those two lefties in the bullpen," Cubs manager Dale Sveum said.
Wells, 29, went 0-1 with a 6.23 ERA in two starts following his recall April 22. He was not happy with the demotion. He walked nine and gave up nine hits over 8 2/3 innings.
"It is what it is," Wells said. "I didn't pitch well. There's no one really to blame but yourself. You obviously want to pitch well and put yourself in a good position, but the numbers don't stack up."
"He's got a future here," Sveum said, "but we can't sit here and promise anything. Right now, that's the role he's in -- the swing man, coming up when we need starts."
The Phillies scored four runs off Wells in the fourth inning on Saturday. Wells, who will be inserted into Iowa's rotation, was upset at the high number of walks in his two starts.
"The walks are the only thing that spoils this," the right-hander said. "I thought I pitched pretty good against the Reds [on April 22]. Five walks [stinks]. The fourth inning in Philly, things unraveled. It's no different than what I've been the last three years -- it's one bad inning. Chalk it up as a bad day and get back to work."
Wood will be eased into games and used in less stressful situations, such as the sixth and seventh innings, Sveum said.
One pitcher in the Cubs' bullpen who hasn't seen much action is Rule 5 Draft pick Lendy Castillo, who has not pitched since April 20.
"When you deal with a Rule 5 guy, you do the best you can," Sveum said. "It's been a luxury to where everything has worked out in a lot of games. We're a month into the season and we haven't had to use him in any stressful situations, and the starters have gone deep enough to give everybody days off, and we've had days off at the right time."
Castillo has appeared in five games so far, and he did see more action when Wood was on the active roster. Wood is the only reliever who won't be expected to go two innings if needed.