A dental safety syringe comprising: a barrel assembly further comprising a reusable barrel and a needle cartridge disposed inside the barrel; and a plunger assembly selectively attachable to the barrel assembly, the plunger assembly comprising a reusable body, plunger handle, a plunger rod and an attachment member configured to selectively and releasably connect the plunger assembly to the barrel assembly, wherein the plunger rod is movable in longitudinal and rotational directions of the reusable body and a distal end of the plunger rod is configured to engage a plug disposed in a proximal end of an ampule, wherein the needle cartridge further comprises a needle, a rearwardly biased needle holder and a distal end which is configured such that from which the needle can be made to project forwardly while administering a medication and then subsequently withdrawn into the needle cartridge to avoid contamination following or between injections, wherein the barrel comprises a sidewall comprising a window (44, 46) through which the needle cartridge is insertable, wherein the barrel assembly and the plunger assembly are interconnected by a combination of cooperatively sized and configured locking members and alignable slots (68, 70, 72) that require both axial and rotational movement of the plunger body relative to the barrel to move the needle to initiate withdrawal of the needle into the needle cartridge, wherein the alignable slots (68, 70, 72) are configured to act as guides for the locking members to facilitate, limit and control both longitudinal and rotational movement of plunger body relative to barrel for at least causing needle holder to move forwardly through an opening at the distal end of barrel to project forwardly into a use position, and after injection causing the reusable body to move rearwardly relative to barrel to allow rearward movement of the rearwardly biased needle holder inside the needle cartridge, withdrawal of the needle into needle cartridge, and separation of the plunger assembly from barrel assembly at the conclusion of the treatment or procedure for removal and safe disposal of needle cartridge and ampule. a barrel assembly further comprising a reusable barrel and a needle cartridge disposed inside the barrel; and a plunger assembly selectively attachable to the barrel assembly, the plunger assembly comprising a reusable body, plunger handle, a plunger rod and an attachment member configured to selectively and releasably connect the plunger assembly to the barrel assembly, wherein the plunger rod is movable in longitudinal and rotational directions of the reusable body and a distal end of the plunger rod is configured to engage a plug disposed in a proximal end of an ampule, wherein the needle cartridge further comprises a needle, a rearwardly biased needle holder and a distal end which is configured such that from which the needle can be made to project forwardly while administering a medication and then subsequently withdrawn into the needle cartridge to avoid contamination following or between injections, wherein the barrel comprises a sidewall comprising a window (44, 46) through which the needle cartridge is insertable, wherein the barrel assembly and the plunger assembly are interconnected by a combination of cooperatively sized and configured locking members and alignable slots (68, 70, 72) that require both axial and rotational movement of the plunger body relative to the barrel to move the needle to initiate withdrawal of the needle into the needle cartridge, wherein the alignable slots (68, 70, 72) are configured to act as guides for the locking members to facilitate, limit and control both longitudinal and rotational movement of plunger body relative to barrel for at least causing needle holder to move forwardly through an opening at the distal end of barrel to project forwardly into a use position,