Is Flossing Actually Necessary? What the Evidence Says

The Headline That Confused Everyone

In 2016, an Associated Press investigation claimed there was little scientific evidence supporting flossing. The story spread rapidly, and many patients arrived at dental appointments asking whether they could simply stop. The truth is more layered.

The AP analysis correctly identified that much of the flossing research used short study durations, small sample sizes, and inconsistent methodology. These are legitimate scientific criticisms. But the conclusion that flossing is therefore useless is a logical leap the data does not support.

Here is the core issue: the absence of robust trial evidence is not the same as evidence of absence of benefit. Interdental surfaces account for a substantial proportion of both caries and periodontal disease. ^[1] Toothbrushing, even with perfect technique, does not reach these surfaces. Something must.

What the Science Actually Shows

A comprehensive 2019 Cochrane systematic review examined the evidence for home use of interdental cleaning devices alongside toothbrushing. ^[1] The review found:

• Flossing plus brushing was associated with a small but statistically significant reduction in gingivitis compared to brushing alone.
• Flossing plus brushing was associated with a reduction in plaque compared to brushing alone.
• The quality of the evidence was rated as low to very low, primarily because of methodological issues in the underlying trials.

The low evidence quality is a reason to call for better research, not to abandon the practice. The biological rationale for interdental cleaning is sound: the interproximal area harbors the specific bacterial communities responsible for both proximal caries and periodontal disease.

The Sequence Matters: Floss Before You Brush

One finding from a randomized controlled trial deserves particular attention. A 2018 study in the Journal of Periodontology found that flossing before brushing, rather than after, led to greater interproximal plaque reduction and higher interdental fluoride concentrations. ^[3] The proposed mechanism is that flossing first disrupts and loosens plaque, then brushing sweeps those loosened particles out of the mouth while simultaneously delivering fluoride into the newly cleaned spaces.

This is a small but meaningful refinement. If you currently brush first and floss after, reversing that sequence may improve the clinical yield of your existing routine.

Floss vs. Interdental Brush: What the Evidence Prefers

Standard dental floss is not necessarily the best interdental tool for every patient. Interdental brushes (also called interproximal brushes or bottle brushes) have been shown in multiple trials to reduce plaque and gingivitis as effectively as, or in some cases more effectively than, floss. ^[2][5]

The key variable is anatomy. In patients with healthy, full interdental papillae (the gum tissue that fills the space between teeth), there is little room for an interdental brush to fit. Floss is better suited to these tighter contacts. In patients with some papillary recession, larger interdental spaces, or bridge pontics, an interdental brush of the appropriate size performs better.

What About Water Flossers?

Water flossers (oral irrigators) generate a pulsating water stream that disrupts supragingival plaque. The evidence for their effectiveness at reducing gingivitis is moderate, and they are generally considered a useful adjunct rather than a replacement for mechanical interdental cleaning. ^[4] They are particularly helpful for patients with orthodontic appliances, implants, or limited manual dexterity.

Why Interdental Cleaning Matters for More Than Just Gums

The focus on gingivitis in much of the research sometimes obscures a related concern: proximal caries. The spaces between teeth, where interdental cleaning is directed, are among the most common sites for cavities in adults. Toothbrushing fluoride delivery is concentrated on buccal and lingual surfaces. The interproximal surfaces receive far less fluoride from brushing alone.

From a biomimetic, preventive standpoint, the goal is to disrupt the biofilm in these areas mechanically and then allow fluoride to reach the freshly cleaned surface. Whatever device achieves that disruption is the right one for that patient.

What the Research Says

The totality of the evidence, reviewed by Cochrane in 2019, supports the following: ^[1][2]

• Interdental cleaning plus toothbrushing is more effective than toothbrushing alone for reducing gingivitis and plaque.
• No single interdental device is universally superior; the best tool is the one the patient will use consistently and correctly.
• Flossing before brushing appears to enhance fluoride delivery to interproximal surfaces. ^[3]
• Water flossers are useful adjuncts, especially for anatomically challenging situations. ^[4]

When to See Dr. Khalid

If you are unsure which interdental tool is appropriate for your anatomy, or if bleeding or discomfort persists despite a consistent routine, a clinical assessment can identify whether there is underlying inflammation that needs addressing. Dr. Khalid can evaluate your interproximal health and guide you toward the most effective approach for your specific situation.