Once, it was a simple question of up and down or round and round. Today, toothbrushing – a basic ritual of personal hygiene – is fraught with decisions: Should you use an oscillating electric brush, or a giant, rubber-flanged monster brush? Is it worth investing in mouthwash, or is tap water just as good?

The main reason we brush our teeth is to remove plaque, a sticky film of bacteria that grows on their surface. Some of these bacteria produce substances that irritate the gums. Others convert sugar into acid, which erodes the teeth. Bacteria also produce stinky substances that cause bad breath. But with so many potential ways of removing plaque from our mouths, how do you know what is best for your teeth? Here’s the latest scientific evidence.

What’s the most effective way to brush your teeth?

The Dental Health Foundation reports that one-in-four Brits think electric toothbrushes are for lazy people. That may be so, but unless you are particularly gifted with a manual toothbrush, they do generally result in cleaner teeth – particularly those with an oscillating head. When the Cochrane Oral Health Group – a group of dentists charged with publishing summaries of the best available evidence – looked at this issue, it concluded that, over three months, using an electric brush was associated with a 21% reduction in plaque and an 11% reduction in gum inflammation compared with manual brushing.

That is not to say that manual toothbrushes are useless, however. “They work pretty well, if you use them properly; the problem is that most people develop a system over time, and it’s not uncommon for them to miss areas,” says Derek Richards, director of the Centre for Evidence-based Dentistry in Dundee. If you prefer to use a manual brush, Richards advises choosing one with a smallish head and medium bristles to ensure that you reach all the nooks and crannies. As for technique, Richards says: “It’s about finding what works for you.”

When should I brush them?

At least twice a day – before bed, and at one other time. An ongoing area of disagreement is whether you should brush before, or after, breakfast. It depends on what you have eaten, says Rebecca Moazzez, director of the oral clinical research unit at Kings College London (KCL) Dental Institute: “The main thing to be careful of is fruit juice or fresh fruit, because they contain acid that can make the surface of the tooth quite soft.” This softening causes some of the calcium and phosphate in the protective enamel to leach out – a process called demineralisation – and if you brush your teeth at this point, you will be brushing some of these minerals away and weakening the teeth. Quite how long you should avoid brushing for remains unclear; the overall pH of the mouth seems to return to normal within minutes, but tooth surfaces may remain soft for up to an hour. “If you want to do anything after eating, I would simply wash with a fluoride mouthwash,” Moazzez says.

Do I have to use toothpaste?

“Brushing protects against gum disease, but it’s the fluoride in toothpaste that prevents tooth decay,” says Maria Therese Hosey, head of paediatric dentistry at KCL. Because of the foods we eat, our teeth are constantly demineralising and remineralising; if fluoride is present during the remineralisation process, it gets incorporated and strengthens the teeth. For this reason, adults should look for a toothpaste that contains at least 1,350ppm fluoride, and steer clear of alternatives such as bicarbonate of soda, which are too abrasive to be used for tooth-cleaning. “Think Brillo pad on a non-stick pan,” says Therese Hosey.

Ironically, failing to remove every last trace of plaque can actually be beneficial for the teeth, because it concentrates fluoride on their surface. For a similar reason, it’s best to avoid rinsing the mouth after brushing. “It means high levels of fluoride are retained on the teeth,” Richards says.

What about mouthwash?

Using a fluoride mouthwash straight after brushing is fairly pointless: you’re flushing away fluoride and replacing it with more of the same. Where it can come in handy, however, is in topping up fluoride levels in between toothbrushing – particularly if you’re at high risk of cavities. “It can also be useful if you have had something acidic to eat, so don’t want to brush,” says Therese Hosey.

Of course, mouthwashes contain more than just fluoride; many contain antiseptic agents such as chlorhexidine, which kill some of the bacteria your toothbrush misses, and help freshen the breath. But while there is some evidence that such mouthwashes can reduce plaque and gum inflammation, Richards says: “If you’re brushing your teeth twice or three times a day with a fluoride toothpaste, the additional benefit you will get isn’t likely to be huge.”

And dental floss?

Plaque accumulates between the teeth, as well as on their surfaces, and this is difficult to remove using a toothbrush alone. The risk here is gum disease, which in its early stages manifests as bleeding when you brush. When the Cochrane Oral Health Group looked at this issue, it concluded that people who brush and floss regularly experience less gum-bleeding compared with those who use brushing alone. However, it said most trials assessing this have been of poor quality.

Similarly, although there is some evidence that interdental brushes are more effective than floss at reducing gum inflammation, the quality of available evidence means it is difficult to say for sure.

Is chewing gum good or bad for teeth?

So long as it is sugar-free, chewing gum is generally a good thing for teeth. For one thing, it stimulates saliva production, which buffers the acid that erodes teeth. It can also help dislodge particles of food from the teeth.

Then there is chewing gum containing xylitol – a low-calorie sweetener that the bacteria responsible for causing tooth decay seem to prefer over sugar. If they are hoovering up less sugar, this means they are producing less acid, which is good news for teeth. What is unclear, however, is how much of this gum we would need to chew to achieve a measurable impact.

What’s the best way to look after children’s teeth?

Milk teeth eventually fall out and get replaced by adult teeth, but if they are left to get so rotten that they have to be prematurely extracted, it can have long-term consequences for your child’s mouth: “Baby teeth guide the position for the permanent teeth, so if you lose a lot of your baby teeth, you’re more likely to have problems later on,” says Richards. Tooth decay is also the number one reason for general anaesthetic use in children, which carries risks of its own.

Although official guidelines recommend brushing children’s teeth fortwo to three minutes, twice a day, as any parent will testify, getting a two-year-old to comply is like asking a crocodile to release your leg from its jaws. “The pragmatic answer is that if you are managing to brush all tooth surfaces using a fluoride toothpaste, then you are doing a pretty good job,” says Therese Hosey.

Do I really need to visit my dentist every six months?

Possibly – if your teeth are in bad shape. But seeing your dentist every six months just for the sake of it could be an unnecessary expense – particularly if they are prone to offering treatments such as a scale and polish each time you visit. The Cochrane Oral Health Group recently concluded that there was no good evidence to support six-monthly dental checkups; a finding echoed by the National Institute of Clinical Excellence. It suggests that children under the age of 18 should see a dentist at least once a year, because their teeth tend to decay faster. For adults who are not experiencing any problems with their teeth, though, every 24 months should be adequate.