A linear cartridge-type motorized dental syringe has a plunger rod aligned with a drive shaft of a motor, the externally threaded plunger rod movable longitudinally, but not rotatably, relative to the casing, a cylindrical body rotated by the shaft, a nut having arm-like nut halves with internal threads engaging external threads on the rod, a locking ring for rotation around an axis of the rod and for longitudinal movement between a rearward position where the ring forces the threads on the nut halves to engage the threads on the rod, and forward where the ring releases engagement of the threads, pusher pins for moving the ring rearward when the cartridge holder is inserted, and a spring for pushing the locking ring back to the forward position, with rotation of the cylinder body resulting in rotative motion of the nut around the rod to move it forward.
