A device for mixing and dispensing a bone cement paste, said device comprising: a housing (H) with a feeding mechanism (13; 23; 33; 53); a cylinder (11; 21; 31;51) for mixing a powder component and a liquid component forming said bone cement paste (P), said cylinder being connected to said housing; a piston assembly comprising a paste feeding member (17; 27; 57) which is located in the cylinder, and a tubular member (14, 24; 34; 54); and a mixing assembly comprising a mixing member (15; 25; 35; 55) which is located in the cylinder, and a mixing rod (12; 22; 32; 52) which extends within said tubular member (14; 24; 34; 54) of the piston assembly, said mixing rod being movable in the tubular member of the piston assembly; wherein said tubular member (14; 24; 34; 54) of the piston assembly is provided with external engagement means (T) by which said paste feeding member (17: 27; 37; 57) is movable within the cylinder (11; 21; 31; 51) in a feeding direction, said feeding movement being operated by the feeding mechanism (13; 23; 33; 53); wherein the device is of single-use type and that it further comprises an actuator assembly (26; 56) which is accommodated in said housing (H) and which in a first position is in engagement with said external engagement means (T) of the tubular member (14; 24; 34; 54), and which in a second position is disengaged from said engagement means (T) for stepwise axial movement of the tubular member (14; 24; 34; 54), in order to move the paste feeding member (17; 27; 57) in the feeding direction; characterized in that asymmetrical stepwise movement of the tubular member (14; 24; 34; 54) is achieved by the tubular member (14; 24; 34; 54) having external engagement means arranged on two sides, namely a first side and a second opposite side ; and wherein the external engagement means on the first side is provided with an axial offset in relation to the external engagement means of the second side . a housing (H) with a feeding mechanism (13; 23; 33; 53); a cylinder (11; 21; 31;51) for mixing a powder component and a liquid component forming said bone cement paste (P), said cylinder being connected to said housing; a piston assembly comprising a paste feeding member (17; 27; 57) which is located in the cylinder, and a tubular member (14, 24; 34; 54); and a mixing assembly comprising a mixing member (15; 25; 35; 55) which is located in the cylinder, and a mixing rod (12; 22; 32; 52) which extends within said tubular member (14; 24; 34; 54) of the piston assembly, said mixing rod being movable in the tubular member of the piston assembly; wherein said tubular member (14; 24; 34; 54) of the piston assembly is provided with external engagement means (T) by which said paste feeding member (17: 27; 37; 57) is movable within the cylinder (11; 21; 31; 51) in a feeding direction, said feeding movement being operated by the feeding mechanism (13; 23; 33; 53); wherein the device is of single-use type and that it further comprises an actuator assembly (26; 56) which is accommodated in said housing (H) and which in a first position is in engagement with said external engagement means (T) of the tubular member (14; 24; 34; 54), and which in a second position is disengaged from said engagement means (T) for stepwise axial movement of the tubular member (14; 24; 34; 54), in order to move the paste feeding member (17; 27; 57) in the feeding direction; characterized in that asymmetrical stepwise movement of the tubular member (14; 24; 34; 54) is achieved by the tubular member (14; 24; 34; 54) having external engagement means arranged on two sides, namely a first side and a second opposite side ; and wherein the external engagement means on the first side is provided with an axial offset in relation to the external engagement means of the second side . <EOS>