We gathered this Q&A off of the CDC website for Infection Control in the Dental Operatory:
Is backflow possible when using a saliva ejector?
Backflow from low-volume saliva ejectors occurs when the pressure in the patient’s mouth is less than that in the evacuator. When patients close their lips and form a seal around the tip of the ejector, a partial vacuum is created. Research suggests that in these situations previously suctioned fluids might be retracted into the patient’s mouth. Furthermore, studies have shown that gravity pulls fluid back toward the patient’s mouth whenever a length of the suction tubing holding the tip is positioned above the patient’s mouth or when a saliva injector is used at the same time as other evacuation (high volume) equipment. Although no adverse health effects associated with the saliva ejector have been reported, dental health care personnel should be aware that backflow could occur when they use a saliva ejector. Practitioners should not advise patients to close their lips tightly around the tip of the saliva ejector to evacuate oral fluids. Suction lines should be disinfected daily. Dentists should contact the manufacturer of the dental unit to review proper use and maintenance procedures including appropriate disinfection methods.
Selected References and Additional Resources
Barbeau J, ten Bokum L, Gauthier C, Prevost AP. Cross-contamination potential of saliva ejectors used in dentistry. J Hosp Infect 1998;40:303–311.
Mann GLB, Campbell TL, Crawford JJ. Backflow in low-volume suction lines: The impact of pressure changes. J Am Dent Assn 1996;127:611–615.
Watson CM, Whitehouse RLS. Possibility of cross-contamination between dental patients by means of the saliva ejector. J Am Dent Assn 1993;124:77–80.