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February 2015
Volume 36, Issue 2

Safety of a Water Flosser: A Literature Review

David L. Jolkovsky, DMD, MS; and Deborah M. Lyle, RDH, BS, MS


Since their introduction more than 50 years ago, water flossers (also known as oral irrigators) have been subject to numerous studies on their safety, efficacy, and delivery of antimicrobial agents, particularly in relation to their ability to impact clinical parameters such as plaque, bleeding, gingivitis, pocket depth, and calculus. Evidence based on such studies and decades of use by the public continues to support their safety and efficacy and disproves suggestions of possible detrimental effects on the attachment, junctional epithelium, or pocket depth.

The first commercially available pulsating oral irrigator was introduced in 1962. The device was a simple plastic container with a motor and tubing that was designed by a dentist and hydraulic engineer to help clean teeth at home (Figure 1 and Figure 2). Research on dental water jets spans more than 50 years and evaluates safety, efficacy, and delivery of antimicrobial agents. More recent studies have examined the host response, impact on individuals living with diabetes, comparison to string floss, and efficacy with implants.

Numerous studies have evaluated the efficacy of pulsated irrigation on multiple clinical parameters, including plaque, bleeding, gingivitis, pocket depth, and calculus. Early studies demonstrated the potential of an oral irrigator used with water to reduce gingivitis, bleeding, and calculus.1-4 Subsequent studies have supported these findings, providing an established body of evidence for daily use of an oral irrigation device for improving oral health.5-10

Many of the studies that provide support for clinical decision-making are randomized controlled, parallel, single-blind studies that have been published in peer-reviewed journals, yet there remains lingering skepticism regarding the safety of irrigation devices. This literature review includes published studies that focus on the safety findings in microscopic and clinical trials.

Histological Findings

In a pilot study by Krajewski et al,11 treatment of 10 subjects with periodontitis who were scheduled for surgery added twice-daily irrigation with water on the left side of the mouth only. Tissue samples were taken at 1, 3, 5, 6, 10, 20, and 25 days of usage. Microscopic findings revealed an increasing improvement at each time point after day 1 for the experimental group (brushing and irrigation), who exhibited less inflammation. In contrast, the control side (brushing only) showed diffuse moderate inflammation and connective tissue disorganization. Canter and Stahl12 evaluated the histological effects of irrigation on inflammation in the area of the col depression. Comparisons were made between excised tissue that was not irrigated and tissue that was irrigated for 4 weeks. The results of the 27 specimens showed a statistically significant decrease in inflammation.

Lainson et al3 evaluated tissue specimens from 20 subjects. Each subject irrigated with water on one side of the mouth. Four specimens from each subject (two experimental, two control) were excised and evaluated in the study. Histological examination of the 40 specimens from periodontal pockets between 3 mm and 6 mm on the experimental side showed fewer inflammatory cells and vascular congestion. These findings were significantly better than those on the 40 non-irrigated specimens. Almost 90% of the subjects showed a more normal gingival condition on the experimental side than on the control side of the mouth.

Reduction in Subgingival Pathogens

The impact of delivering water or an antimicrobial agent into the pocket has been evaluated for impact on the subgingival microflora. An ultrastructural study by Cobb et al13 evaluated the impact of water irrigation on the epithelial wall of the periodontal pocket and the morphologic types of bacteria found at different levels (0 mm to 2 mm, 3 mm to 4 mm, and 5 mm to 6 mm). Periodontally involved teeth were irrigated for 8 seconds prior to extraction and excisional biopsy. Using scanning electron microscopy, the irrigated sites showed considerable reductions in the number of microorganisms compared to the control group. Specifically, there were very few cocci and rods and no fibrin-like matrix in the 0 mm to 2 mm and 3 mm to 4 mm levels, as compared to control. Thick mattes of organisms, including spirochetes, were seen in control specimens at the 5 mm to 6 mm area. In contrast, the test specimens showed a light fibrin-like network and the rare spirochete. Transmission electron microscopy showed no differences in the cell walls between the groups. The authors concluded that there was a qualitative change on the subgingival biofilm, no evidence that irrigation is injurious to the tissue, and the appearance of a quantitative difference in the number of microbes and amount of debris in the irrigation group. Drisko et al14 also demonstrated a reduction of spirochetes in sites up to 6 mm that were irrigated with water.

Newman et al15 compared the effects of rinsing with 0.12% chlorhexidine gluconate (CHX), irrigating with 0.06% CHX, and irrigating with water on the marginal and subgingival microflora in subjects with gingivitis. All subjects and the control group brushed with a sodium fluoride dentifrice. Data was collected at baseline, 3 months, and 6 months. Comparisons were made for Gram-positive cocci and rods, Gram-negative rods, and Gram-negative anaerobic rods and black-pigmented Bacteroides for logarithmic transformation (log10) of colony-forming units (CFU) and proportions (percent). At 6 months, the CHX irrigation group was significantly better than brushing in reducing the CFU10 log and percent of Gram-negative anaerobic rods and percent of black-pigmented Bacteroides. CHX rinsing only demonstrated a significant difference compared to brushing for CFU log at 6 months. Water irrigation did not demonstrate any significant benefits compared to the other groups in this study.

Sanders et al16 found no significant differences between non-irrigated and irrigated sites for most organisms measured from pockets that were ≥ 4 mm comparing 0.02% CHX, 0.05% metronidazole, 0.01% quinine sulphate inactive control, and non-irrigated site. There were some isolated differences between the groups for cocci at certain time points favoring the irrigation sites. In this study, all sites were scaled and root planed after baseline plaque samples were taken. In contrast, Chaves et al17 found that Prevotella intermedia was significantly reduced from baseline in the water irrigation group at 6 months and the 0.04% CHX irrigation group at 3 months. No significant differences were noted for the CHX rinsing and the brushing group. In a study by Jolkovsky and colleagues,18 each subject in the experimental groups received a professional irrigation after scaling and root planing of either sterile water or 0.12% CHX. The subjects then irrigated daily with either water or 0.04% CHX using a tip designed to be placed 1 mm to 2 mm subgingivally. Wolinella recta and black-pigmented Bacteroides were significantly reduced in the group that received the professional CHX irrigation and who also irrigated at home with 0.04% CHX for 3 months.

Irrigation with essential oils showed a decrease in total bacterial cell counts19 and putative periodontopathogens, including black-pigmenting species20 at 6 weeks. Hurst and Madonia21 found that water irrigation was 80% more effective at reducing the total aerobic flora and 60% more effective at reducing lactobacillus counts in adolescent subjects with fixed orthodontic appliances when measured by saliva samples.

Pocket Depths and Clinical Attachment Levels

The assumption that a pulsating stream of water negatively impacts the junctional epithelium, especially in periodontitis patients, lacks evidence, as proven by the following studies. These studies specifically evaluated clinical attachment levels (CAL) and/or probing pocket depths (PPD).

Al-Mubarak et al22 evaluated 52 subjects with either type 1 or type 2 diabetes and chronic periodontal disease. The subjects were enrolled in a single-center, single-blind, 3-month clinical and laboratory study. All subjects received a scaling and root planing treatment and were randomly assigned to either normal oral hygiene group (a manual toothbrush and any interdental device they used before the study) or the irrigation group with a subgingival tip plus normal oral hygiene. At 3 months, the irrigation group showed significantly better improvement in measures, including gingivitis, plaque, and bleeding on probing (BOP), compared to controls, and patients’ serum levels of interleukin-1 beta (IL-1β) and Prostaglandin E2 (PGE2) were significantly reduced from baseline. This demonstrates a host modulation effect, and of importance for safety is the finding that there were no negative changes in the CAL or PPD for either the test group or the control group. The mean probing depth for the test group was 3.55 mm at baseline and 3.23 mm at week 12; for the control group, these numbers were 3.65 mm and 3.40 mm, respectively. Similar findings were recorded for the CAL, with the test group measured at 3.8 mm at baseline and 3.7 mm at 12 weeks, and the control group at 4.2 mm and 3.98 mm in the same time period.

Cutler and colleagues23 were the first to measure the impact of daily irrigation on the inflammatory process. In this study, they measured pro-inflammatory mediators in the gingival crevicular fluid (GCF) at 14 days along with clinical parameters, including PPD. Oral irrigation with water plus routine oral hygiene (ROH) resulted in a significant reduction in PPD, BOP, gingival index (GI), and plaque index (PI), as well as a down modulation of pro-inflammatory mediators. In this study of mild-to-moderate periodontitis subjects, the PPD reduction was significantly better than the ROH group.

A group of 155 subjects who were previously treated for periodontal disease and were receiving supportive periodontal maintenance therapy was enrolled in a 6-month, single-blind, multi-center study.24 Subjects had a minimum of two teeth in different quadrants with 5-mm PPD or more that bled upon probing. All subjects continued with their recommended oral hygiene routine. The group that added water irrigation demonstrated a significantly better reduction in gingival inflammation, BOP, and PPD. Similarly, Flemmig et al25 found significant improvements in a study of 60 subjects with periodontitis receiving supportive periodontal therapy for gingivitis, probing pocket depths, and bleeding on probing.

Chaves et al17 explored the mechanisms involved in the treatment of gingivitis by water irrigation. Subjects with fewer than four sites with probing pocket depths deeper than 6 mm and frequency of bleeding on probing of 30% or greater were included in the study. Probing pocket depth was measured at baseline, 3 months, and 6 months, along with BOP, GI, and PI. The subjects were randomized into four groups: brushing only, brushing and water irrigation, brushing and chlorhexidine rinsing (0.12%), and brushing and CHX irrigation (0.06%). There was no change in the PPD for any of the groups at 3 or 6 months. Only the irrigation groups (with or without CHX) showed consistent microbial changes that were not seen in the rinsing or brushing-only groups.

An early study that evaluated the use of an essential oil as the daily irrigant compared to placebo—both of which were delivered with an oral irrigator—showed there were no statistically significant differences in PPD or CAL at the end of the 6-week study. Of significance is that there was no difference between the scaled and unscaled sites.19

Other researchers looked at the effect on inflammation and safety in gingivitis subjects. A 6-month study26 evaluated the impact of brushing paired with 0.06% CHX irrigation compared to brushing with 0.12% CHX rinsing, brushing plus water irrigation, or brushing only. CHX irrigation demonstrated a significantly lower PPD score compared to brushing alone. There were no differences between the other groups.


Manipulation of oral tissue will cause bacteria to enter the blood steam (bacteremia), especially in people with ulcerated epithelial tissue, as seen in various levels of periodontal disease. There was an assumption that oral irrigation produced a higher incidence of bacteremia. The incidence of bacteremia using a pulsating oral irrigator ranges from 7% in people with gingivitis27 to 50% in people with periodontitis.28 These percentages are similar to other self-care devices: tooth brushing and flossing (20% to 68%), use of wooden toothpicks or sticks (20% to 40%), and mastication (7% to 51%).29,30 Considering the frequency of these daily activities, the focus has moved to improving access to dental care and eradicating dental disease rather than on the routine use of prophylactic antibiotics.


The evidence shows that using a pulsating oral irrigation device, also known as a water flosser, is safe and effective (Table 1). This is based on decades of use by the public and a body of evidence that has not reported any adverse effects. Specifically, the device does not push bacteria into the pocket, but can significantly remove the bacteria, improving the clinical signs of inflammation. There is no evidence of detrimental effects on the attachment or junctional epithelium; and, in some cases, a reduction in the pocket depth has been reported.

In making clinical decisions that are in the best interest of the patient, it is important to be guided by the evidence and disregard anecdotal or incorrect information, assumptions, and personal biases. A plethora of studies conclusively show that daily use of a water flosser is safe. Not all irrigators have the same specifications, and research findings for one device are not transferable to other brands or designs.

About the Authors

David L. Jolkovsky, DMD, MS

Lecturer, UCLA School of Dentistry; Private Practice, Davis, California; Diplomate, American Board of Periodontology

Deborah M. Lyle, RDH, BS, MS

Director of Research, Water Pik, Inc., Fort Collins, Colorado


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