Are interdental brushes better than floss?

For gaps large enough to accept one, yes — the evidence base for interdental brushes is stronger and more consistent than for floss. The Salzer et al. (2015) meta-review in the Journal of Clinical Periodontology rated the interdental brush the most effective device for removing interdental plaque, and the European Federation of Periodontology's 2020 guideline names it the first-choice device where the space permits. Floss remains the correct tool for tight contacts where no brush will fit.

Does flossing actually work, or was the 2016 story right?

The 2016 Associated Press investigation correctly reported that the evidence for flossing is of low quality — small, short, poorly designed trials. But low-quality evidence does NOT mean flossing does not work. It means the size of the benefit has never been well measured. The Cochrane review (Worthington et al., 2019) still found that flossing plus brushing reduces gingivitis compared with brushing alone, just with low certainty. Floss was never debunked; it was under-studied.

What is the best way to clean between teeth?

Use an interdental brush wherever one fits, and floss the gaps where it does not. Do it once a day, ideally at night before brushing, and cover every gap. Most adult mouths need both tools and two or three different interdental brush sizes. The Australian Dental Association advises cleaning between the teeth every day and asking your dentist which device suits your gaps.

What interdental brush size do I need?

There is no single answer — gap sizes vary across one mouth, so most people need two or three sizes. The correct brush slides in with light resistance and never needs to be forced. If it rattles through without touching both tooth walls it is too small and is doing nothing. If you have to push it in, it is too large and will traumatise the gum. Ask your dentist or hygienist to size you; it takes two minutes.

Should I stop if my gums bleed when I use an interdental brush?

No. Bleeding when you first start interdental cleaning is expected. It is inflamed gum tissue being cleaned for the first time, not an injury caused by the brush — healthy gums do not bleed. In most people it settles within one to two weeks as the inflammation resolves. If bleeding is still present after two to three weeks of daily, correctly-sized cleaning, book a dental assessment.

Is a water flosser as good as an interdental brush?

No. A water flosser reliably reduces gum bleeding and is far better than doing nothing, but it does NOT disrupt the plaque biofilm as thoroughly as a brush or floss physically scrubbing the tooth surface. Water flossers are genuinely the right choice for braces, bridges, implants and for people with arthritis, tremor or limited dexterity — but for most people they supplement mechanical cleaning rather than replace it.

How often should I clean between my teeth?

Once a day is enough, and it is what the evidence supports. Interdental plaque takes roughly 24 hours to mature into a damaging biofilm, so one thorough daily disruption does the job. Twice-daily interdental cleaning has not been shown to beat once-daily and increases the risk of gum trauma. Do it at night, before brushing.

What is the correct way to floss?

Use roughly 45cm of floss. Guide it between the teeth with a gentle sawing motion — never snap it straight down, which cuts the gum. Curve it into a C-shape against one tooth, slide it 2–3mm below the gum line, and move it up and down. Then re-curve it against the other tooth in the same gap and repeat. Use a fresh section of floss for every gap.

Interdental Brushes vs Floss: What The Evidence Says

📖 11 min read · Updated 30/06/2026

Quick Summary

✔ For gaps big enough to take one, interdental brushes have the stronger evidence base than floss for reducing plaque and gum bleeding

✔ Floss is the right tool for tight contacts where no brush will physically fit — it is not obsolete, it is second-choice

❌ The 2016 "flossing doesn't work" headlines were misread — low-quality evidence does NOT mean no effect

✔ The Cochrane systematic review (Worthington et al., 2019) found interdental brushes plus brushing may reduce plaque and gingivitis more than brushing alone

✔ Size is everything with an interdental brush — too small does nothing, too large traumatises the gum. Most mouths need 2–3 sizes

✔ Bleeding for the first 1–2 weeks of interdental cleaning is expected and is not a reason to stop

❌ The only genuinely wrong answer is doing neither

Quick Answer

In the interdental brushes vs floss debate, the evidence favours the brush. Systematic reviews of interdental cleaning — including the Cochrane review by Worthington and colleagues (2019) and the meta-review by Sälzer and colleagues in the Journal of Clinical Periodontology (2015) — consistently rate interdental brushes above floss for removing interdental plaque and reducing gingival bleeding, in people whose gaps are large enough to accept a brush. Floss remains the correct tool for tight contacts where a brush cannot physically pass. The practical rule: use an interdental brush wherever one fits, and floss the gaps where it does not. Once a day, every day. Doing neither is the only choice the evidence clearly condemns.

Why Interdental Cleaning Exists At All

A toothbrush — manual or electric, cheap or expensive — cannot reach the surfaces between your teeth. The bristles ride over the contact point. They clean the outer face, the inner face and the chewing surface, and then they skip the two flat walls that face each other across the gap. Roughly 40% of each tooth's surface area sits in that blind spot.

That blind spot is not a cosmetic problem. It is the exact anatomical site where gum disease most commonly begins. The interdental papilla — the small triangle of gum that fills the space between two teeth — is the first tissue in the mouth to become inflamed when plaque is left undisturbed, and it is almost always the first place bleeding shows up.

So when someone tells you they brush twice a day and their gums still bleed, they are usually not lying and they are usually not brushing badly. They are simply cleaning the 60% of the tooth that was never the problem. If you want the full picture on why gums bleed, read What Causes Bleeding Gums: Every Cause Explained.

The core principle

Gum disease starts between the teeth. A toothbrush cannot go between the teeth. Therefore brushing alone — no matter how good — is NOT a complete oral hygiene routine. Interdental cleaning is not an optional extra. It is the half of the job most people skip.

The 2016 Flossing Story, Told Honestly

In August 2016 the Associated Press published an investigation by reporter Jeff Donn examining the evidence behind daily flossing. It found that the studies underpinning the recommendation were small, short, poorly designed, or industry-funded — and that the US federal dietary guidelines had quietly dropped their flossing recommendation because the evidence had never been formally reviewed. The story went global under headlines along the lines of "flossing doesn't work".

That headline was a misreading, and it is worth being precise about why.

"Weak evidence" does NOT mean "doesn't work"

Low-certainty evidence means we cannot be confident in the size of the effect — the trials were too small, too short, or too sloppy to measure it well. It does NOT mean the effect is zero. Absence of high-quality evidence is NOT evidence of absence. The Cochrane reviews of flossing did not find that floss fails. They found that the trials testing it were of low quality, and that within those limits floss plus brushing still reduced gingivitis more than brushing alone.

There is also a mundane reason floss tests badly: most people floss incorrectly. A trial that recruits ordinary people, hands them floss, and measures their gums three months later is not testing floss. It is testing floss-as-performed-by-untrained-humans-who-mostly-do-not-do-it. Studies that include supervised, taught flossing tend to show clearer benefit. That is a real-world limitation of floss, not a reason to dismiss it — but it is one of the strongest arguments for the brush, which is dramatically harder to get wrong.

What The Evidence Actually Says About Interdental Brushes

The interdental brush has quietly accumulated the better evidence base — and, more importantly, the more consistent one.

Source	Year	What It Found
Cochrane systematic review — Worthington et al., Home use of interdental cleaning devices, in addition to toothbrushing	2019	Reviewed the randomised trials of flossing, interdental brushes, wood sticks, water flossers and more. Concluded that using an interdental device in addition to toothbrushing may reduce gingivitis and plaque, but that the certainty of the evidence overall was low to very low. Interdental brushes were among the better-performing devices for plaque reduction.
Sälzer, Slot, Van der Weijden & Dörfer — meta-review of interdental mechanical plaque control, Journal of Clinical Periodontology	2015	Synthesised the systematic reviews of interdental cleaning. Reported that the interdental brush is the most effective device for removing interdental plaque, and that the evidence for floss providing an additional benefit over brushing alone was weak and inconsistent.
Slot et al. — systematic review of interdental brushes, International Journal of Dental Hygiene	2008	Found interdental brushes removed more plaque than toothbrushing alone, and performed at least as well as, and in several comparisons better than, floss.
European Federation of Periodontology S3-level clinical practice guideline (Sanz et al., J Clin Periodontol)	2020	Recommends professionally taught interdental cleaning as part of managing gingivitis, with interdental brushes as the first-choice device where the interdental space allows one.
Australian Dental Association (ADA)	current	Advises cleaning between the teeth every day, using floss or an interdental brush — and asking your dentist which is right for the size and shape of your gaps.

Read that table carefully, because the honest summary is nuanced. The evidence for interdental brushes is better than the evidence for floss — but the evidence base for interdental cleaning as a whole is not as strong as anyone would like. Dentistry has never funded the large, long, well-blinded trials that cardiology takes for granted. The direction of the effect is consistent across every review. The size of it is not well measured. Anyone telling you either device is "clinically proven" to a specific percentage is selling you something.

Bleeding when you clean between your teeth is a signal, not a stop sign.

LACALUT® Aktiv — the German clinical system with aluminium lactate, chlorhexidine 0.25% and sodium fluoride. Founded 1925.

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Interdental Brushes: How To Use One Properly

An interdental brush is a small cylindrical or tapered bristle head on a wire core, sold in graded sizes — typically colour-coded from the very fine (for tight spaces) to the very wide (for large gaps and around bridges). It works by physically scrubbing both tooth walls at once, which is precisely what floss struggles to do.

Size Is Everything

This is the single point most people get wrong, and it is the reason so many people buy a pack of interdental brushes, use them for a week, and conclude they do nothing.

If the brush is...	What happens	Result
Too small	The bristles pass through the gap without touching both tooth walls	You feel like you are cleaning. You are NOT. Plaque stays exactly where it was.
Correct	Slides in with light resistance; bristles flex against both walls; comes out with a faint scraping feel	The interdental surfaces are actually cleaned. This is the goal.
Too large	It has to be forced; the wire may bend; the gum blanches or is cut	Gum trauma and, over time, recession. Forcing a brush is worse than using none.

The size rule

The correct brush slides in with light resistance and never needs force. If you have to push, it is too big. If it rattles through with no contact, it is too small. Most mouths need two or three different sizes across different gaps — the space between your front incisors is nothing like the space between your back molars. A single-size pack is almost never the right answer. Ask your dentist or hygienist to size you at your next visit; it takes two minutes and it is the highest-value two minutes in preventive dentistry.

Technique

Step	Action	Why
1	Choose the size that fits the gap you are working on — not the size you started with	Gap sizes vary hugely across one mouth
2	Insert straight in at the gum line, angled slightly towards the biting surface	Follows the natural shape of the interdental space
3	Push in and out gently, 2–3 times	The in-out stroke is what disrupts the plaque biofilm
4	Never force it. If it will not go, drop a size — or use floss on that gap	Forcing cuts the papilla and drives recession
5	Rinse the brush and move to the next gap	Prevents transferring plaque between sites
6	Replace the brush when the bristles splay or the wire bends — roughly weekly	A bent wire is a gum injury waiting to happen

Floss: Still The Right Tool For Tight Contacts

Floss is not obsolete. It is the correct instrument for a specific job: the gaps where no interdental brush will physically fit. If your teeth are tightly packed — and if you have never had gum recession, they very likely are — then for those contacts floss is not the second-best option. It is the only option.

The catch, as the trial evidence suggests, is that floss is easy to do badly. Most people saw it back and forth across the contact point, snap it into the gum, and never take it below the gum line — which is where the plaque that causes gum disease actually lives.

The C-Shape Technique

Step	Action	Common Mistake
1	Use about 45cm of floss; wind most of it around one middle finger and the rest around the other	Using one short piece for the whole mouth — you just move plaque around
2	Guide the floss between two teeth with a gentle sawing motion until it passes the contact point	Snapping it straight down. This cuts the papilla and is the number one cause of floss injury
3	Curve the floss into a C-shape against the side of ONE tooth	Holding it straight, which cleans neither wall properly
4	Slide it gently 2–3mm below the gum line, then move it up and down against the tooth wall	Stopping at the gum line — the plaque you are chasing lives just under it
5	Re-curve the floss against the OTHER tooth in the same gap and repeat	Doing one wall and moving on — the gap has two surfaces, both need cleaning
6	Unwind a fresh section of floss and move to the next gap	Re-using the same dirty section across all 28 teeth

Floss picks — the little plastic Y-shaped holders — are a reasonable compromise. They make the C-shape harder to achieve, so they are technically inferior to string floss. But a floss pick you actually use every night beats string floss you keep in the drawer. Adherence beats theoretical superiority.

Water Flossers: Where They Fit

Water flossers (oral irrigators) fire a pulsed jet of water into the interdental space. They are genuinely useful, and they are genuinely oversold.

The reasonable reading of the evidence is that a water flosser is better than nothing by a wide margin, and consistently reduces gingival bleeding scores — but it is NOT as effective at physically disrupting the plaque biofilm as a brush or floss that mechanically scrubs the tooth surface. Plaque is a sticky, structured biofilm. Water pressure flushes debris and disturbs the loose surface; a bristle or a filament shears it off.

Who a water flosser is genuinely right for

People with fixed orthodontic braces, bridges, implants or splints, where a brush or floss cannot navigate the hardware. People with arthritis, tremor, limited dexterity or one working hand, for whom threading floss is not realistic. And people who flatly will not do anything else — in which case a water flosser used nightly is worth far more than an interdental brush used never.

Head-To-Head: Interdental Brush vs Floss vs Water Flosser

Device	Strength Of Evidence	Best For	Limitations
Interdental brush	Strongest of the three. Rated the most effective interdental plaque-removal device in the Sälzer et al. (2015) meta-review; first-choice device in the EFP 2020 guideline where the gap permits.	Any gap large enough to accept a brush. Gum recession, larger interdental spaces, bridges, implants, molars, existing gum disease.	Will NOT fit tight contacts. Requires correct sizing — the wrong size is either useless or harmful. Usually needs 2–3 sizes per mouth.
Floss	Weaker and less consistent. Cochrane (2019) rated the evidence low-certainty. Reduces gingivitis versus brushing alone, but effect size is poorly measured. Low quality of evidence does NOT mean no effect.	Tight contacts where no brush fits — which for most people is the front teeth and any un-recessed contact point.	Technique-sensitive: most people snap it down, skip below the gum line, and re-use one section. Poor real-world adherence.
Water flosser	Mixed. Reliably reduces bleeding scores and clearly beats doing nothing, but does NOT disrupt the plaque biofilm as thoroughly as mechanical cleaning.	Braces, bridges, implants, splints, crowns. Arthritis, tremor or limited dexterity. Anyone who refuses to use anything else.	Flushes debris rather than shearing biofilm. Costs more, needs power and bench space, needs cleaning. Not a full substitute for a brush or floss.

So Should You Use A Brush Or Floss? The Verdict

The verdict

Use an interdental brush wherever one fits. Use floss on the gaps where it does not. Once a day, every day, every gap. That is not a compromise position — it is what the evidence actually supports. The brush has the better data and is far harder to use wrongly; floss covers the contacts the brush physically cannot enter. Most adult mouths need both. And the only genuinely wrong answer — the one every systematic review agrees on — is doing neither.

Do it once a day, not twice. Interdental plaque takes roughly 24 hours to reorganise into a mature, damaging biofilm, so a thorough daily disruption is enough. Twice-daily interdental cleaning has never been shown to beat once-daily, and it increases the risk of gum trauma from over-enthusiastic technique.

Do it at night, before brushing. Cleaning between the teeth first lifts the interdental plaque out of the gap, so the fluoride in your toothpaste can then reach the surfaces it was blocked from.

Bleeding When You Start: Expected, Not A Reason To Stop

Almost everyone who starts interdental cleaning after a long gap bleeds. Often for the first several nights. This alarms people, and a great many of them conclude they are injuring themselves and quietly stop. It is the single most common reason interdental cleaning routines fail.

The bleeding is NOT the brush injuring healthy tissue. It is inflamed, plaque-laden gum tissue — already engorged with fragile capillaries — being touched for the first time. Healthy gums do not bleed when cleaned properly. Bleeding is the diagnosis, not the injury.

Timeline	What To Expect	What To Do
Days 1–3	Bleeding at most or all gaps. Possibly some tenderness.	Keep going. Gently. Do not skip the bleeding gaps — those are the ones that need it most.
Days 4–10	Bleeding reduces. Fewer sites bleed, and less.	Keep going. Daily. Do not miss a night.
Weeks 1–2	In most people, bleeding largely settles as the inflammation resolves.	This is the outcome you were after. Maintain it.
Beyond 2–3 weeks	Persistent bleeding despite daily, correctly-sized interdental cleaning.	Book a dentist. This suggests calculus below the gum line that home care cannot reach, or established periodontitis.

For what that persistence means and how far it can be walked back, see Can Gum Disease Be Reversed? What The Evidence Actually Says and 7 Warning Signs Of Gum Disease You Should Never Ignore.

Where Toothpaste Fits Into This

Interdental cleaning is mechanical. It disrupts the biofilm. What you brush with afterwards is chemical — and the two are complementary, not interchangeable. No toothpaste will clean a surface it never touches, and no interdental brush delivers fluoride.

LACALUT^® Aktiv is a German clinical formulation built around aluminium lactate, chlorhexidine 0.25% and sodium fluoride, from a brand founded in 1925. It is designed for people whose gums bleed and who are serious about their daily routine — the exact people who should also be cleaning between their teeth every night. The LACALUT Aktiv 2-Part System pairs the toothpaste with the mouthwash, and the sample pack includes dental floss so there is no excuse to skip the half of the job that matters most. If you want the full routine in one box, the Aktiv Complete System adds the toothbrush.

Clean between your teeth. Then brush with something that earns its place.

LACALUT® Aktiv — aluminium lactate, chlorhexidine 0.25% and sodium fluoride. German clinical oral care since 1925.

Shop The LACALUT Aktiv System

Medical disclaimer: This article is for general information only and does not constitute dental or medical advice. Interdental brush sizing should be assessed by a registered dental practitioner. If your gums bleed persistently, book a dental assessment.

Frequently Asked Questions — Interdental Brushes vs Floss

Question	Answer
Are interdental brushes better than floss?	For gaps large enough to accept one, yes — the evidence base for interdental brushes is stronger and more consistent than for floss. The Salzer et al. (2015) meta-review in the Journal of Clinical Periodontology rated the interdental brush the most effective device for removing interdental plaque, and the European Federation of Periodontology's 2020 guideline names it the first-choice device where the space permits. Floss remains the correct tool for tight contacts where no brush will fit.
Does flossing actually work, or was the 2016 story right?	The 2016 Associated Press investigation correctly reported that the evidence for flossing is of low quality — small, short, poorly designed trials. But low-quality evidence does NOT mean flossing does not work. It means the size of the benefit has never been well measured. The Cochrane review (Worthington et al., 2019) still found that flossing plus brushing reduces gingivitis compared with brushing alone, just with low certainty. Floss was never debunked; it was under-studied.
What is the best way to clean between teeth?	Use an interdental brush wherever one fits, and floss the gaps where it does not. Do it once a day, ideally at night before brushing, and cover every gap. Most adult mouths need both tools and two or three different interdental brush sizes. The Australian Dental Association advises cleaning between the teeth every day and asking your dentist which device suits your gaps.
What interdental brush size do I need?	There is no single answer — gap sizes vary across one mouth, so most people need two or three sizes. The correct brush slides in with light resistance and never needs to be forced. If it rattles through without touching both tooth walls it is too small and is doing nothing. If you have to push it in, it is too large and will traumatise the gum. Ask your dentist or hygienist to size you; it takes two minutes.
Should I stop if my gums bleed when I use an interdental brush?	No. Bleeding when you first start interdental cleaning is expected. It is inflamed gum tissue being cleaned for the first time, not an injury caused by the brush — healthy gums do not bleed. In most people it settles within one to two weeks as the inflammation resolves. If bleeding is still present after two to three weeks of daily, correctly-sized cleaning, book a dental assessment.
Is a water flosser as good as an interdental brush?	No. A water flosser reliably reduces gum bleeding and is far better than doing nothing, but it does NOT disrupt the plaque biofilm as thoroughly as a brush or floss physically scrubbing the tooth surface. Water flossers are genuinely the right choice for braces, bridges, implants and for people with arthritis, tremor or limited dexterity — but for most people they supplement mechanical cleaning rather than replace it.
How often should I clean between my teeth?	Once a day is enough, and it is what the evidence supports. Interdental plaque takes roughly 24 hours to mature into a damaging biofilm, so one thorough daily disruption does the job. Twice-daily interdental cleaning has not been shown to beat once-daily and increases the risk of gum trauma. Do it at night, before brushing.
What is the correct way to floss?	Use roughly 45cm of floss. Guide it between the teeth with a gentle sawing motion — never snap it straight down, which cuts the gum. Curve it into a C-shape against one tooth, slide it 2–3mm below the gum line, and move it up and down. Then re-curve it against the other tooth in the same gap and repeat. Use a fresh section of floss for every gap.