Brushing your teeth: what the evidence actually supports

Brushing advice has accumulated a lot of ritual. Some of it matters a great deal, some of it makes no measurable difference, and at least one very common habit actively undoes the thing you just did. It is worth separating them.

The number on the tube is the active ingredient

Toothpaste is mostly a delivery vehicle. Its flavour, foam and abrasive content contribute very little to preventing decay. The fluoride does, and the concentration is printed on the tube in parts per million.

The Cochrane review of fluoride toothpaste concentrations found that the benefit compared with a non-fluoride paste is only statistically significant at 1000 ppm and above, and that the effect increases with concentration. Around 1000 to 1250 ppm delivers roughly a 23 percent reduction in decay, with higher concentrations doing more.

This is worth checking, particularly on toothpaste bought for children, because a number of products marketed for young children are dosed well below that threshold. Fluoride level in young children does need balancing against the risk of fluorosis while the permanent teeth are forming, which is a conversation to have with us rather than a rule to apply blindly, but an under-dosed paste is doing very little.

Spit, do not rinse

If you like using a fluoride mouthwash, use it at a different time of day rather than immediately after brushing, where it dilutes a stronger product with a weaker one.

Technique beats effort

The goal is disrupting plaque at the margin where the tooth meets the gum, because that is where gum disease starts. Plaque is soft. It does not need scrubbing off; it needs the bristles to physically reach it.

• Use a soft brush. Medium and hard brushes do not clean better and they do cause abrasion. Splayed bristles after a few weeks mean you are pressing far too hard.
• Angle the bristles at about 45 degrees toward the gum line rather than straight at the tooth, and use small circular or short back-and-forth movements. Long horizontal scrubbing is what carves notches into the necks of teeth.
• Two minutes, twice a day. Most people substantially overestimate how long they brush; timing it once is genuinely informative.
• Make one of those times last thing at night. Saliva flow falls during sleep, so both the fluoride and any remaining sugar sit undisturbed for hours.
• Do not brush for about thirty minutes after vomiting or after acidic food and drink. Enamel is temporarily softened and brushing at that moment removes the softened layer.

The surfaces a brush cannot reach

A toothbrush cleans three of the five surfaces of a tooth. The two contact surfaces where each tooth meets its neighbour are left largely untouched, and a substantial share of decay and most early gum disease begins in precisely those spots.

Interdental brushes are the more effective option wherever the space allows one to fit, and they are easier to use consistently than floss. Floss is for the tight contacts where a brush will not pass. The choice between them matters far less than doing one of them daily, and the useful reframing is that this is not an optional extra on top of brushing but the other half of the job.

Electric or manual

Powered brushes, particularly oscillating-rotating designs, show a modest but consistent advantage in reducing plaque and gingivitis in reviews of the evidence. The advantage is real but smaller than most marketing implies, and it is dwarfed by whether you brush twice a day, for long enough, at the right angle, with a fluoride paste you do not rinse away.

Where powered brushes genuinely help is with pressure. Many have a sensor that stops you pressing too hard, and for the substantial number of people whose brushes are splayed after a month, that alone is worth it. The built-in timer helps too.

What brushing cannot fix

Brushing controls plaque. It does not address how often you eat, and the frequency of sugar intake is at least as strong a driver of decay as cleaning is. Someone brushing impeccably twice a day while sipping sweet tea from a flask all afternoon will still get cavities, because the tooth is spending most of the day below the pH at which enamel dissolves.

Nor does brushing remove calculus once plaque has hardened, and it cannot reach into a periodontal pocket. Those need professional cleaning. The realistic division of labour is that you control the daily biofilm and we handle what has become inaccessible to you.