Patent ID: 8840585

Claim:
A motorized syringe for use with two types of dental anesthetic solution-filled cartridges, comprising a syringe body, a cartridge holder adapted to be connected to said syringe body by means of a coupling, said cartridge being loaded in said cartridge holder, a push rod having a rack formed thereon, and a pinion engaged with said rack and adapted to be rotated by a drive unit, the engagement of said rotating pinion with said rack moving said push rod slowly forward, thereby pushing a plunger rubber plug in said anesthetic solution-filled cartridge for delivery of said anesthetic solution from said cartridge through a needle, wherein said cartridge holder is configured to be capable of being used in common for both of 1.0 ml and 1.8 ml cartridges, said push rod has a 1.0 ml cartridge-setting position and a 1.8 ml cartridge-setting position drawn back from said 1.0 ml cartridge-setting position so that forward movement of said push rod ends at a common terminal position for both the 1.0 ml and 1.8 ml cartridges, the syringe comprises a bottomed sleeve adapted to receive a rear end portion of said push rod therein when said push rod is pushed back from said common terminal position, and to be not interfered with by a rear end face of the push rod when the push rod is in the 1.0 ml cartridge-setting position, said sleeve being pushed rearwardly with the rear end face of said push rod when the push rod is pushed back to the 1.8 ml cartridge-setting position, and the syringe comprises a return spring for moving forward said sleeve together with said push rod upon its forward movement.