The theta-matrix compositor is a device aboard Federation starships in the 24th century, such as the Galaxy-class and the Intrepid-class. It is used to recrystalize dilithium crystals while still in the articulation frame of a warp core. (TNG: "Family", VOY: "Innocence"). Dilithium recrystalization was first theorized and attempted by Captain Spock aboard a commandered Klingon bird of prey in the 23rd century (Star Trek IV: The Voyage Home)