In Japanese, deppa 出っ歯 means having upper teeth that protrude forward, ending up outside the mouth.
Literally, deppa 出っ歯 means "leaving teeth." A "tooth" or "teeth, ha 歯, that "leaves," deru 出る, the mouth. The ha は becomes ppa っぱ due to handakuonka 半濁音化.
Anime: Game Center Arashi, ゲームセンターあらし (Episode 1)