Interdental Brushes, Floss and Water Flossers: Choosing a Size, Order of Use and What to Do When They Won't Fit

Should I use floss or an interdental brush?

The criterion is to use each according to the size of the space in each area [2]. Toothbrush bristles do not reach the contact surfaces between teeth, so cleaning between teeth with floss or interdental brushes is the foundation for preventing cavities and gum disease [1]. The role of each tool is as follows.

Tool	Suitable areas	Role
Interdental brush	Areas with an open gap, for example from gum recession	Removes plaque in wider spaces between teeth [2]
Floss	Areas where teeth are too tight for an interdental brush	Scrapes plaque off the sides of teeth [2]
Water flosser (oral irrigator)	Supplementary tool	Helps rinse away food debris; cannot replace physical removal of plaque [2]

When DentStat analyzed about 1,600 patient comments on interdental cleaning tools from YouTube dental content, typical questions were “the interdental brush won’t go in,” “do I have to buy every size?” and “if I have a water flosser, can I skip floss?” [3].

How do I choose an interdental brush size, and what if it won’t fit?

The criterion is a thickness that slides through smoothly without resistance, and where no size fits, floss is used instead [2]. Too loose and it cleans less; too thick and it risks damaging gums and tooth surfaces, so many people use different thicknesses together to match the different spacing between teeth [2]. Forcing a brush in can cause damage, so the principle by area is floss for tight spots and interdental brushes for open ones [2]. The comment analysis repeatedly showed frustration that “even the thinnest one won’t go in” and questions like “do I have to buy every size?” [3].

How should I use floss?

Rather than sawing back and forth, the recommended method is to wrap the floss gently against the side of the tooth and sweep it up and down from the gum line [2]. Sawing only sideways can cut the gums or leave plaque on the tooth surface, so the basic motion is to wrap each tooth surface and sweep along it [2]. Bleeding at first is often a sign that the area was inflamed, and it often decreases with regular use [2]. If the same spot keeps bleeding despite continued use, other causes such as tartar below the gum line need to be checked by a dentist [1]. In the comments, reactions such as “I used floss like a saw” or “I stopped because it bled” appeared often [3].

If I have a water flosser, can I skip floss and interdental brushes?

They have different roles, so it is described as not a full replacement [2]. A water jet is a supplement for rinsing away food debris, but plaque (biofilm) stuck to tooth surfaces does not come off with water pressure alone, so physical removal with floss or interdental brushes is needed [2]. A commonly suggested order is brushing first, then floss or interdental brushes between teeth, with a water flosser or mouthwash as a supplement, but the key is not the order but never skipping cleaning between teeth [1]. In the comments, hopes that it could replace floss, such as “the water flosser worked better” and “with a water flosser, I’m set for life,” were seen repeatedly [3].

Common misconceptions and the facts

• Myth: “Interdental brushes push teeth apart.” → Fact: The right size only cleans space that is already there; gaps that look wider are often swollen gums shrinking back to reveal the original space [2].
• Myth: “With a water flosser, you don’t need floss.” → Fact: Rinsing with water is described as unable to replace physical removal of plaque [2].
• Myth: “If it bleeds, stop using the tool.” → Fact: Bleeding at first is a common reaction; only persistent or repeated bleeding needs a dentist [2].
• Myth: “Floss and interdental brushes are the same, so one is enough.” → Fact: They clean different areas and complement each other [2].

Brushing technique and oral care basics are covered in the oral care basics guide, gum symptoms and treatment in the gum disease guide, tartar care in the scaling guide, and regional clinic data in Find a dentist.