WASHINGTON — Dennis Seidenberg returned to the Islanders’ lineup Thursday night after missing seven games because of a broken jaw. He’d been one of the Isles’ best defensemen during the first 15 games, pairing with Calvin de Haan to provide a surprising bit of offense as well as steady play in the defensive zone.

Having his jaw wired shut and being off solid food for three weeks (with another two weeks to go) has made keeping his weight up a challenge.

“It’s the weight and getting enough oxygen in,” Seidenberg said. “I’ve been skating since the injury so I’m not too worried about conditioning. I don’t think I should have a problem.”

Jack Capuano said Scott Mayfield, who played on Wednesday night and was superb in the win over the Penguins, didn’t deserve to sit again but that Seidenberg has been too valuable to keep out once he was ready.

To make room on the roster for Seidenberg, the Islanders placed Adam Pelech on injured reserve (retroactive to Monday) with an upper-body injury suffered in the second period of the Isles’ overtime win over the Flames.

The Capitals were hosting German Heritage Night on Thursday night, seemingly the right time for the German-born Seidenberg to return.

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“Maybe I can get a bratwurst after the game,” he said. “Well, not yet — can’t eat it.”

Quine in for Beauvillier

The only other lineup change from Capuano was Alan Quine taking Anthony Beauvillier’s spot on a line with Jason Chimera and Nikolay Kulemin. Beauvillier had played eight straight since being scratched in back-to-back games in early November, but this was more a rest issue for the 19-year-old than punishment.