The system and method disclosed herein prevent a patient from interrupting the vacuum created by the vacuum line attached to the saliva ejector so that suction continues to be present even if the patient clamps his or her lips tightly about the shaft of the saliva ejector. In the illustrated embodiment, the backflow prevention mechanism includes a sleeve positionable on the shaft of the saliva ejector and engageable by the patients lips. The sleeve includes at least one conduit that remains open to allow air to enter the patients mouth even when the patients lips are tightly closed. The air entering the patients mouth via the at least one conduit enables the vacuum line to continue to draw bodily fluids and contaminants from the patients mouth.
