Abstract: A capsule for dental compositions has a mixing chamber for mixing a dental composition that contains a first component of the dental composition and has a bottom with an outlet opening for the dental composition. A piston is positioned in an initial position at an upper end of the mixing chamber. The piston has at least one recess and an inner chamber containing a second component of the dental composition. The inner chamber has a bottom in the form of a temporary seal. A plunger is positioned in an initial position at an upper end of the inner chamber of the piston. Upon depressing the plunger, the temporary seal is broken to introduce the second component into the mixing chamber. A manually removable U-shaped locking member has two legs and a connecting bar connecting the legs wherein the connecting bar is elongate in a direction pointing away from the legs to form a grip portion.