ST. LOUIS -- Down 3-2 in the Stanley Cup Final against the St. Louis Blues, the Boston Bruins are making lineup changes to shake things up.

Boston will revert back to a traditional lineup of six defensemen and 12 forwards in Game 6 on Sunday night in St. Louis, with rookie forward Karson Kuhlman drawing in for the first time since April 30. Defenseman Steven Kampfer will be bumped from the lineup in Game 6.

"It's just a decision we made to be a little different," coach Bruce Cassidy said.

Defenseman Matt Grzelcyk, who has been out since Game 2 with a concussion, is still not cleared, according to Cassidy.

Kuhlman, a 23-year-old rookie out of Minnesota-Duluth, has played in six playoff games this spring, registering two assists. However, he has been a healthy scratch since Game 4 of the second-round series against the Columbus Blue Jackets. Cassidy said he likes Kuhlman's motor.

Kuhlman will play on a line with David Krejci and Jake DeBrusk, a spot where David Backes has typically played. Backes, a longtime former Blues player, is not expected to play in the pivotal game.

Kuhlman said he's "just excited about" the chance to play in a Stanley Cup Final.

"I think [Cassidy] and I are on the same page," Kuhlman said. "We know what I can do to help this team."

Cassidy said the challenge for Kuhlman -- as it has been with all Bruins forwards -- "is getting inside" St. Louis' big defensive corps.

With captain Zdeno Chara playing in Game 5 with a reported broken jaw, the Bruins opted to dress seven defensemen in a precautionary move. Cassidy said his staff was not sure how much Chara would be able to play, and how playing would affect his breathing.

Chara, however, played 16:42 minutes in the game, although he appeared uncomfortable at times. Nonetheless, the seven-defenseman rotation is not ideal as it doesn't allow for blueliners to find a true rhythm in a game and can overwork forwards that need to double-shift.

The move to insert Kuhman is likely to help get Krejci going as the two have played together at other times this season. Krejci has been held without a point in five games this series.

The Bruins also need more from their talented top line. David Pastrnak, Brad Marchand and Patrice Bergeron have yet to score a five-on-five goal in this series. Though the top line has been red-hot for stretches during these playoffs, the Bruins have relied heavily on their depth to get them this far. Twenty different Boston players have scored this postseason.

"Your best players need to be your best players, but if they defend well and we have a good defensive game, you know, we're in it, I feel someone will step up," Cassidy said Saturday. "Probably them, because they usually do. But same token, we don't want to put so much pressure on them they get outside their overall game, their defensive game, because they're a good line all around and we don't want them to lose that."

The Bruins are hoping to force a Game 7 on home ice. It would mark the first time the Stanley Cup Final went to seven games since 2011 -- when the Bruins defeated the Vancouver Canucks for their most recent championship.

"We're obviously going to come out with the will and desire to compete, and they are, too," defenseman Torey Krug said. "There's pressure on both sides. If [they] don't win tonight then they have to come into a Game 7 in our building and that's pressure for them, I'm sure. For us, our season could end but we're coming into it with the right mentality that we're going to force a Game 7 and ultimately, it comes down to will and who wants it more."