A toothbrush reaches about three of the five surfaces of each tooth. The two surfaces where teeth touch are where a large share of decay starts and where gum inflammation persists — and nothing you do with a brush will clean them.
This is the step most people skip, and it is the step that decides whether gums stay healthy.
Floss or interdental brushes?
For most adults, interdental brushes are more effective where they fit. They clean a wider area, they are easier to use well, and most people are more likely to persist with them. Floss remains the right tool where the gap is too tight for even the smallest brush — commonly between the front teeth, and in younger people with tight contacts.
Many people end up using both: brushes for the back teeth, floss at the front.
The size matters more than the choice. An interdental brush that is too small passes through without touching anything; too large and it will not go in or it damages the gum. Different gaps in your mouth need different sizes, and you are unlikely to guess them — ask at your next appointment to be sized properly. It takes two minutes and it is the difference between doing this and doing it usefully.
How to use an interdental brush
- Choose the size that fits the space with slight resistance but no force.
- Insert it gently and horizontally into the space at the gum line, at a slight angle following the gum contour.
- Push in and pull out two or three times. Do not scrub side to side.
- Move to the next space. Rinse the brush as needed.
- Replace the brush when the bristles splay, usually after a week or two.
If you have to force it, go smaller. If it goes through with no contact at all, go larger.
How to use floss
- Take about 45 cm and wind most of it around one middle finger, the rest around the other, leaving a few centimetres between.
- Guide it between two teeth with a gentle sawing motion — do not snap it down onto the gum.
- Curve it into a C-shape against one tooth and slide it gently just below the gum margin. This is the part that matters and the part most people omit.
- Move it up and down against that tooth surface a few times.
- Curve it against the other tooth in the same space and repeat.
- Use a fresh section as you move along.
Snapping floss straight down and straight back out cleans almost nothing. The C-shape against each tooth in turn is the whole technique.
What about water flossers?
Useful, particularly around bridges, implants, orthodontic appliances and where dexterity is limited. They flush debris and reduce bleeding.
They are best thought of as an addition rather than a replacement. A water jet disrupts a biofilm less effectively than physical contact does, so where floss or an interdental brush will fit, use one of those and add the water flosser if you find it helpful.
Floss picks are better than nothing and much better than skipping. They make the C-shape difficult, so they are a compromise rather than the ideal.
When, and how often
Once a day is enough. Before brushing is marginally better than after, because it loosens plaque from between the teeth so the fluoride in your toothpaste can reach those surfaces.
Evening usually works best, because it is the one time of day most people are not rushing — and the night-time clean matters most, since saliva flow drops during sleep.
Be systematic. Start in one place and work around the whole mouth in the same order every time, including behind the last tooth on each side. Approximate cleaning misses the same places repeatedly.
What to expect in the first fortnight
If your gums are inflamed, they will bleed when you start. This alarms people into stopping, which is the one response that guarantees the problem continues.
Inflamed tissue bleeds when disturbed. Keep going, gently and daily, and expect bleeding to reduce over one to two weeks and largely stop. If it has not, see a dentist — there may be hardened tartar below the gum line that cannot be reached, or the disease may have progressed beyond the gum. See bleeding gums: what they mean.
Special situations
Bridges and implant bridges: units are joined, so floss cannot pass between them. Use superfloss or a floss threader to get underneath the span — see looking after your implants.
Fixed retainers: same problem, same solution.
Braces: a floss threader under the archwire, plus interdental brushes — see keeping teeth clean with braces.
Black triangles: where gum has receded between teeth, interdental brushes are far more effective than floss.
Crowded teeth: floss may be the only thing that fits. Be patient and use a waxed floss.
Frequently asked questions
Is flossing really necessary?
Cleaning between the teeth is. Whether you do it with floss or interdental brushes is a practical question, and for most adults brushes work better.
Before or after brushing?
Before, so fluoride reaches the cleaned surfaces. Either is far better than neither.
My gums bleed when I floss. Should I stop?
No — it is the clearest sign you need to keep going. It should settle within two weeks.
How do I know what size interdental brush to use?
Ask to be sized at your next appointment, with your own teeth in front of you.
Does mouthwash do the same job?
No. Rinsing does not physically remove a biofilm from between two touching surfaces.
Ask to be shown and sized
Two minutes at a check-up doing this on your own teeth is worth more than any written instruction. See our professional cleaning page.
To arrange a consultation at our clinic on Abbas El-Akkad in Nasr City, call +20 101 969 7597 or message us on WhatsApp.
