Systems for maintaining a vacuum in a patient's oral cavity comprises an oral device, a vacuum control system, and an assembly including first and second tubes for connecting the vacuum control system to the oral device. The oral device has an internal plenum, and a vacuum is drawn in the plenum by a vacuum pump connected by a first tube of the tubular assembly. The vacuum is maintained by an air source which is connected to the plenum by the second tube of the tubular assembly. By maintaining a constant circulating air bleed through the oral device and the connecting tubes, saliva may be removed from the system and collected in a saliva trap located before the vacuum pump.