Flossing before brushing removes more plaque and leaves more protective fluoride on your teeth than brushing first. That said, the difference is modest enough that the American Dental Association considers either order acceptable. The best sequence is the one you’ll actually stick with every day.
What the Research Shows
A clinical study published in the Journal of Periodontology tested both sequences on the same group of participants, measuring plaque levels and fluoride concentration after each routine. When people flossed first and then brushed, they had significantly less plaque overall compared to brushing then flossing. The fluoride from toothpaste also remained in the mouth at higher levels when flossing came first.
The logic is straightforward. Flossing loosens bacteria and food debris from between your teeth and along the gumline. When you brush afterward, the toothpaste and bristles sweep that loosened material away. The fluoride in your toothpaste can also reach the newly cleared spaces between teeth, where cavities commonly form. If you brush first and floss second, you dislodge material but don’t have that second pass with fluoride-rich toothpaste to clean it out and protect those surfaces.
Why the ADA Says Either Order Works
Despite the evidence favoring flossing first, the American Dental Association doesn’t take a hard stance. Their official position: “Either way is acceptable as long as you do a thorough job.” The ADA acknowledges that some people prefer flossing first to sweep material out, while others like starting with a clean mouth before working floss between their teeth.
This permissive stance exists for a practical reason. Only about 30% of Americans floss daily, and dental professionals would rather you floss in whatever order feels natural than skip it because the “right” sequence feels like one more barrier. A complete flossing routine in any order beats a skipped one.
The Habit Factor
Here’s where it gets interesting. Research on habit formation from the British Journal of Health Psychology found that people who were told to floss after brushing actually formed stronger flossing habits over time. At an eight-month follow-up, the “floss after” group flossed more frequently than those told to floss before brushing.
The likely explanation is that brushing is already an automatic habit for most people. When you attach a new behavior (flossing) to the end of an existing one (brushing), the established habit acts as a reliable trigger. Flossing first requires you to remember to do it before your usual routine kicks in, which is a harder mental ask. So while flossing first may give you a slight edge in plaque removal on any given day, flossing after brushing may help you floss more consistently over months and years. Consistency matters more than sequence.
Does This Apply to Water Flossers?
The same general principle holds for water flossers. Using one before brushing lets your toothbrush and toothpaste follow up on the debris you’ve blasted loose. WebMD notes that while you can use a water flosser before or after brushing, studies support the “before” sequence for better plaque removal. A water flosser doesn’t replace traditional floss or brushing, but the order logic is identical: loosen first, clean second.
Interdental brushes, which are small bristled picks designed for the gaps between teeth, work the same way. Using them before your toothbrush gives the fluoride in your toothpaste better access to those in-between surfaces.
What Actually Matters Most
The plaque reduction advantage of flossing first is real but not dramatic. What makes the biggest difference to your gum health and cavity risk is whether you floss thoroughly and consistently, not when you do it relative to brushing. If you currently don’t floss at all, picking either order and committing to it daily will do far more for your oral health than optimizing the sequence.
If you’re looking for the technically optimal routine: floss first, brush second, and don’t rinse your mouth with water immediately after brushing (this lets fluoride sit on your teeth longer). If that sequence feels awkward or you find yourself skipping the floss, switch to flossing after brushing and don’t worry about it. The margin between the two orders is small compared to the gap between flossing regularly and not flossing at all.