The specification discloses a dental syringe having a head, a tip and a releasable coupling mounted on the head. The head and tip have a corresponding number of fluid passages therethrough. The coupling includes a cylindrical base and a lock nut which screws over the base. The base and the lock nut define an axially extending bore which communicates with the passages through the head and removably receives the rearward portion of the tip. An elastomeric O-ring is positioned between the base and the lock nut and surrounds the bore. When the rearward portion of the tip is fully inserted in the bore the O-ring seats in a groove surrounding the rearward portion of the tip. When the lock nut is fully screwed over the base, deformation of the O-ring is substantially prevented and the tip cannot be withdrawn or ejected from the coupling.