Every three months, or sooner if the bristles have splayed. That is Oral-B's guidance and ours. The number is the easy part; remembering it is where most of us come unstuck, so this guide is mostly about making the change happen without having to think about it.
Why three months?
Oral-B's UK guidance is that dental professionals recommend a new brush head every three months, or sooner if you notice frayed bristles. Its reasoning is practical: worn bristles lose their ability to remove plaque, and plaque left behind can lead to gum problems, tartar and bad breath.
You can see it happen. A new head has upright bristles with defined tips that reach along the gumline and into the grooves of your back teeth, which is exactly where plaque collects. As the bristles wear, they bend outwards and lose their spring. A splayed head feels softer, and people often prefer it, but that softness is the head no longer reaching where it needs to.
The signs it is time, whatever the calendar says
- The bristles splay out past the edge of the head.
- The indicator bristles have faded. On iO Ultimate Clean heads they fade from blue to white as a reminder.
- The bristles have lost their bounce. Press them with your thumb; they should spring straight back.
- Your iO9 says so. Its display reminds you when the head is due, and the Oral-B app keeps track of how long you have been using it.
If your heads wear out in six weeks
When a head is flattened well before three months, the usual culprit is pressure. Heavy brushing wears bristles quickly, and the Oral Health Foundation warns that brushing too hard can damage teeth and gums as well. The fix is not more heads; it is a lighter touch.
Judging your own pressure by feel is hard, which is why pressure feedback is the feature we rate most highly on an electric toothbrush. The Oral-B iO9 Black Onyx shows you, as you brush, when your pressure is too hard, too soft or just right. Ease off, and your gums and your heads will thank you.
What changing on time costs
| How you buy | Price | Lasts one person | Cost per day |
|---|---|---|---|
| One-off four-pack | £20 | 12 months | About 7p |
| Subscribe and save 10% | £18 | 12 months | About 6p |
About £1.67 a month for a head that is doing its job. Put like that, stretching a worn one for another couple of months stops looking like a saving.
The easy way: a four-pack and a subscription
In our experience, the commonest reason people keep brushing with a worn head is not forgetfulness. It is that there was no spare in the cupboard at the moment they noticed. So keep a four-pack of genuine iO Ultimate Clean heads in the bathroom, and let a subscription replace it.
Choose subscribe and save on the product page and your next four-pack arrives every 12 months for one person, or every six months for two people, at £18 instead of £20. Add a quarterly reminder on your phone for the first of January, April, July and October, and between the reminder, the fading indicator bristles and the iO9's display, the head change takes care of itself.
Check the fit before you order
Oral-B iO heads fit Oral-B iO toothbrushes, including the iO9, and nothing else. Pro, Vitality, Smart, Genius and Pulsonic brushes use a different fitting, and the heads do not swap in either direction. Our iO heads guide explains the difference, and why a genuine head matters. Every pack of Oral-B iO replacement heads we sell is genuine Oral-B iO.
Questions we get asked
Can I clean a head instead of replacing it?
Rinse it well after brushing and let it dry upright in the air; that is worth doing every day. But no amount of cleaning straightens bristles that have bent and lost their spring.
Should everyone have their own head?
Yes, always. Never share a brush head, even with a partner.
Does a worn head damage my teeth?
The bigger problem is what it leaves behind. Oral-B's reasoning is that worn bristles remove less plaque, which can lead to gum problems. If your heads wear out fast because you brush hard, the pressure itself is worth fixing.
Why buy your heads from Onyx
Every head we sell is genuine Oral-B iO Ultimate Clean, chosen by practising dentists to go with the iO9. Subscribe and save 10% and the spares arrive on schedule. Order before 4pm and it is dispatched the same day; delivery is free on orders from £50; unopened packs can come back within 30 days; and if you are unsure which head fits your brush, ask us and one of our dentists will reply.
Buying the brush too? The £180 Complete Care Bundle includes the iO9, this four-pack and a Biorepair Plus toothpaste, saving £11.98 on the three bought separately.
Shop the iO Ultimate Clean four-pack, £20, or subscribe and save 10%
Sources
- Oral-B UK: replacement brush heads
- Oral-B UK: why should you replace your brush head?
- Oral-B UK: iO Ultimate Clean heads, black, four-pack
- Oral Health Foundation: electric toothbrushes
- Onyx product page, subscription options and delivery and returns page, checked 30 September 2026.