A pump assembly for a dental cleaning appliance includes a fluid chamber, a piston, and a drive. The drive rotates a coupling member having two angularly opposed pins. An arm pivotably connected to the piston has a seat for receiving one of the pins to couple the piston to the drive. Through continued rotation of the coupling member, the piston moves within the fluid chamber to draw fluid into the fluid chamber until the second detent contacts the arm to push it away from the first detent to decouple the drive from the piston. This allows a compressed spring to actuate the piston to urge a burst of fluid from the fluid chamber.