How often you should replace a toothbrush

Three months is a reminder, not a rule

Three months is the interval most people have heard, and it works as a reminder rather than an expiry date. Nothing changes inside the brush on the day those three months are up. Picture two people buying the same brush on the same morning: one brushes twice a day with a light grip, the other scrubs in a hurry before work. Three months later the brushes are the same age and in very different condition.

The date makes life easier, but it does not make the decision. Treat it as an upper limit: rather than waiting for the three months to run out, look at the bristles every few weeks and change the brush early once they have spread.

The bristles are the real measure

On a new brush the tufts stand close together, and the tips stay compact enough to reach the line where the tooth meets the gum. With use the tips flatten and the tufts splay outwards. Flattened bristles lift less plaque for the same movement, so the cleaning falls off even though your two minutes have not changed. Holding the brush up to the light now and then shows this better than any date.

• The tufts have spread outwards and the outline of the head looks ragged
• The tips have flattened, so the brush looks squat when you view it from the side
• The coloured indicator bristles have faded, or lost their colour halfway down
• Bristles are working loose or dropping out at the base of a tuft

Heavy pressure wears a brush out sooner

The harder you press, the sooner the bristles flatten. A brush that splays well before three months usually says more about your grip than about the brush: the next one will look the same after six weeks. Holding the handle like a pen, working from the wrist rather than the arm and using small circles instead of scrubbing is easier on the bristles and on the gums.

However new the brush is, a surface the bristles never touch does not get cleaned, and the surface missed most often is the back of the last molar.

After an illness

Replacing a brush after flu, a throat infection or anything that leaves sores in the mouth is a common habit. Catching the same illness again from your own brush is not something to expect, yet starting the recovery with a fresh brush is a sensible step and most dentists see no harm in it. What matters more is that brushes standing in one glass never touch head to head.

How long an electric brush head lasts

On an electric brush the part you change is the head, and because its bristles are shorter, splaying shows up earlier than on a manual brush. The box usually quotes something close to three months, but the measure is the same: once the bristles have spread, the head is finished whatever the calendar says. If your brush has a pressure sensor and it warns you often, that head is wearing out faster than average.

What does not work

Holding splayed bristles under hot water to straighten them does not bring the brush back. The tufts may look tidier for a moment, but they never regain their original narrow shape, and water hot enough to soften the plastic bends them further out of line. Boiling the brush, running it through the dishwasher or putting it in the microwave all end the same way. Sharing a brush with someone else is never a sensible option.

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