Preventing Evacuation Line Backflow

In clinical dental settings, evacuation line backflow is an often-overlooked health risk to patients. The inadvertent reversal of fluid from the evacuation line back into patients’ mouths can lead to cross contamination, potentially exposing them to blood, saliva, bacteria, and tissue remnants from previous procedures. In the 1990s, several groundbreaking studies were published that shed light on the prevalence, causes, and risks associated with backflow.^1-3 However, without government-mandated preventive measures, backflow may take a back seat to other pressing safety and sanitization concerns. Fortunately, advances in technology have made it easier than ever for dentists, dental hygienists, dental assistants, and other dental healthcare professionals to seamlessly incorporate backflow prevention safety measures into their existing treatment practices and cleaning and disinfection routines.

Understanding Backflow

Also known as “suck-back” or “backwash,” backflow is similar to what can occur when two people share a drinking straw. They may inadvertently swallow saliva or debris left in the straw by the other person. But in dental evacuation lines, what causes the fluid to reverse direction and reach the next patient’s mouth? The answer lies in the saliva ejectors, which are designed to suction fluids into the evacuation line. The US Centers for Disease Control and Prevention (CDC) explains that “backflow from low-volume saliva ejectors occurs when the pressure in the patient’s mouth is less than that in the evacuator.”⁴

Backflow Prevalence and Causes

Pioneering researchers Watson and Whitehouse were the first to identify backflow as an issue in the dental industry.¹ They conducted trials to investigate the occurrence of backflow and the factors that contribute to it when using saliva ejectors in dental procedures and published their findings in an article in the Journal of the American Dental Association ( JADA ) in 1993. Watson and Whitehouse found that one out of every five patients experienced backflow through the saliva ejector. They also discovered that backflow was only experienced by the patients who closed their lips around the saliva ejector, causing a drop in intraoral pressure. Patients who kept their mouths open were unaffected. Moreover, Watson and Whitehouse reported that 91% of the dental offices that participated in their study were unknowingly contributing to the incidence of backflow by asking or prompting patients to close their mouths around saliva ejectors.

In a follow-up article published in the June 2024 issue of JADA , Vinh and colleagues revealed that most dental healthcare professionals continue to prompt this behavior.⁵ About seven out of every ten of the dentists, dental assistants, and dental hygienists that they surveyed reported that they ask patients to close their lips around the tip of the saliva ejector during suction use/procedures. In another study by Barbeau and colleagues that was published in 1998 in the Journal of Hospital Infection , the results indicated that backflow is a direct result of pressure changes, which can occur not only when patients close their mouths around saliva ejectors but also when the suction tubing is positioned above patients’ mouths, when patients’ cheeks, tongues, or other intraoral structures block the tip of the saliva ejector, or when a saliva ejector is used at the same time as other high volume evacuation equipment (Figure 1 through Figure 3). The third scenario certainly has implications for today’s dental professionals given that the study by Vinh and colleagues reported that 74% of dentists, 67% of dental assistants, and 42% of dental hygienists use low volume suction simultaneously with high volume evacuation equipment.

Health Risks

The study by Barbeau and colleagues examined water samples collected from the saliva ejector tubing and surfaces where bacteria or other microorganisms grew in the evacuation lines. They found low levels of bacteria in 24% of their samples, confirming the potential for the spread of disease through backflow. In the landmark 1993 study, Watson and Whitehouse identified viable bacteria in the suction lines of all of the dental units that they tested. Most of the organisms were oral in origin, which indicated that saliva, blood, and other remnants from previous dental procedures were being trapped in the evacuation tubing and posing a cross contamination risk to patients.

The Watson and Whitehouse study also found that 27% of the participating dental practices only cleaned and disinfected their evacuation lines once a week, which meant that infection-causing material likely lingered in the lines for days across numerous patients and procedures. Of the other practices that participated in the study, 23% reported that they rinsed and disinfected suction lines between patients, 41% reported that they rinsed and disinfected suction lines once a day, and 9% reported that they rinsed and disinfected suction lines twice a week.

Unfortunately, the survey results published in the 2024 follow-up study by Vinh and colleagues showed little to no improvement in this area (Figure 4).^1,5 The percentag e of dental offices that reported cleaning and disinfecting evacuation lines daily increased slightly from 41% to 43%; however, the percentage that reported cleaning and disinfecting the lines after each patient decreased from 23% to 22% and the percentage that reported cleaning and disinfecting the lines once a week decreased from 27% to 22%. In addition, 10% of the offices reported they were only cleaning and disinfecting the evacuation lines once a month, and 3% reported that they didn’t know how often they were servicing the lines. The 2024 study also broke down the results by job title. In total, 74% of the dentists, 65% of the dental assistants, and 53% of the dental hygienists reported cleaning the evacuation lines either between each patient or daily. Nevertheless, that means that 26% of the dentists, 35% of the dental assistants, and 47% of the dental hygienists admitted to only weekly, monthly, or an unknown frequency of evacuation line cleanings in their dental offices.

Preventive Strategies

In 2003, the CDC addressed backflow in its report, “Guidelines for Infection Control in Dental Health-Care Settings—2003.” The agency cited Watson and Waterhouse, Barbeau, and other peer-reviewed studies and offered recommendations to reduce the risk of backflow and uphold infection control standards, including the following:

• Do not encourage patients to close their lips around the saliva ejector, and ensure that their tongues, cheeks, or other oral anatomy do not block the tip.

• Ensure that suction tubing is positioned below patients’ mouths during procedures.

• Regularly clean and disinfect evacuation lines to prevent cross contamination between patients and procedures.

• Avoid using high volume evacuation equipment while using low volume suction devices, such as saliva ejectors.

Backflow Prevention Technology

When the CDC published its guidelines in 2003, effective backflow prevention technology was still in development. Now, dental practices have access to whole lines of backflow prevention devices, such as the Safe-Flo™ Saliva Ejectors and Valves. Safe-Flo products offer a reliable solution because they feature a unique, built-in, one-way valve mechanism. The valve prevents backflow by immediately closing in response to vacuum pressure changes, creating a physical barrier against fluid reversal to safeguard patients (Figure 5).

With devices such as the Safe-Flo saliva ejectors and valves, dental healthcare professionals don’t have to worry about patients accidentally closing their mouths around the saliva ejector tips, either out of habit, nervousness, or because they’re younger patients or patients with disabilities who cannot modify their behavior. In fact, the American Academy of Pediatric Dentistry “encourages dental practitioners to follow current literature and consider carefully infection control measures in their practices to minimize the risk of microbial transmission” in its recently updated “Policy on Infection Control.”⁶ Using devices such as the Safe-Flo saliva ejectors and valves may provide a way to reduce the risk of backflow, no matter the patient or procedure. This may also increase dental healthcare professionals’ confidence when using low volume and high volume suction equipment at the same time, freeing them up to work more efficiently.

A Call to Action

Backflow represents a common yet preventable risk in clinical dental settings with the potential to compromise patient safety and infection control protocols. By adopting backflow prevention strategies and embracing innovative solutions, such as Safe-Flo products, dental practices may be able to reduce this risk, ensuring a safer and more hygienic environment for every patient encounter and upholding the highest standards of patient care.

About the Author

Mindy Gil, DMD, DMSc, is a diplomate of the American Board of Periodontology and a fellow of The American Academy for Oral & Systemic Health. She maintains a private practice in Newnan, Georgia.

References

1. Watson CM, Whitehouse RLS. Possibility of cross-contamination between dental patients by means of the saliva ejector. J Am Dent Assoc. 1993;124(4):77-80.

2. Mann GL, Campbell TL, Crawford JJ. Backflow in low-volume suction lines: the impact of pressure changes. J Am Dent Assoc. 1996;127(5):611-615.

3. Barbeau J, ten Bokum L, Gauthier C, Prévost AP. Cross-contamination potential of saliva ejectors used in dentistry. J Hosp Infect. 1998;40(4):303-311.

4. US Centers for Disease Control and Prevention. Guidelines for infection control in dental health-care settings—2003. MMWR Recomm Rep. 2003;52(RR-17):1-61.

5. Vinh R, Azzolin KA, Stream SE, et al. Dental unit waterline infection control practice and knowledge gaps. J Am Dent Assoc. 2024;155(6):515-525.e1.

6. American Academy of Pediatric Dentistry. Policy on infection control. AAPD website. https://www.aapd.org/research/oral-health-policies--recommendations/infection-control/. Accessed September 3, 2025.