The invention relates to a pneumatic injection device adapted to be connected with an air outlet of a dental chair for providing a compressed air flow, comprising: an injection unit comprising a unit body having a proximal end, a distal end and a cavity between the proximal and distal ends for receiving a dental cartridge, wherein the distal end has an injection needle connector for connecting a needle, and the proximal end is connected to an air seal adaptor in an airtight relationship; an output pressure selector having an output end connected air-tightly to the other end of the air seal adaptor; an air releasing means having an output end connected air-tightly to an input end of the output pressure selector; and an input pressure adjustor having an output end connected air-tightly to an input end of the air releasing means, an input end for connection to the air outlet of the dental chair.