How to prevent and stop tooth decay

Lincoln Hirst BDS
Written by the Dental Fear Central Web Team and reviewed by Lincoln Hirst BDS
Last updated on July 13, 2021
  1. Leave at least 3.5 to 4 hours between eating or drinking things that contain sugars or starches.
  2. Brush twice a day for at least 2 minutes, ideally before breakfast and before going to bed. Use an electric toothbrush and toothpaste with 1350-1500ppm fluoride. Spit out the toothpaste and don’t rinse.
  3. Clean between teeth once every day with interdental brushes and/or floss.

If you’d like to delve deeper and truly understand the “why’s” and “how’s” behind these recommendations, read on!

Are some people more prone to tooth decay than others?

Until quite recently, tooth decay was classified as an infectious disease, caused by bacteria such as S. Mutans. This view has changed.1.

We now know that tooth decay is primarily caused by eating or drinking “free sugars” too frequently.

Frequent exposure to sugars changes the community of microorganisms in the mouth. This can result in tooth decay.

Genetics may make some people more prone to hosting more “bad” than “good” microbes. People with dry mouth are also more prone to getting tooth decay.

But even if you’re prone to tooth decay, you can do a lot to prevent it.

What are free sugars?

“Free sugars” include:

• any sugars added by the producer during the preparation of food or drinks (e. g. sugar, glucose syrup, fructose)

• any sugars you add yourself. This includes “natural” products such as honey or syrup.

• all fruit juices (and fruits that have been juiced, e.g. in smoothies)

How can tooth decay be prevented?

To recap, the main cause of tooth decay is the frequency or the number of times per day that sweet or starchy things are placed in the mouth.

The simple secret is to make a decision to leave 3.5 to 4 hours between eating or drinking them.

This gives the teeth a chance to remineralise. It also means that you automatically reduce the number of acid attacks to 4 to 5 per day.

Have what you want! — 3.5 – 4 hour break — Have what you want!

If you feel that you must eat something in the Recovery Time, make sure that it is sugar-free.

What exactly is tooth decay, and what causes it?

If you’re the kind of person who likes to know why and how things happen, here’s an explanation:

Tooth decay is a process which softens and eventually destroys the hard tissues of the tooth. For tooth decay to develop, you need 3 things:

  • bacteria
  • fermentable carbohydrates, and
  • susceptible tooth substance.
Example of foods containing fermentable carbohydrates, which can cause tooth decay if eaten too frequently

What are fermentable carbohydrates?

Carbohydrates (sugars and starches) are found in most foods, including

  • sweets and desserts
  • fruit and fruit juice
  • bread
  • breakfast cereals
  • pasta
  • potatoes
  • rice
  • soft drinks

to name but a few. Almost all carbohydrates are fermentable2.

A notable exception are the “sugar alcohols”. Unlike their name suggests, these are neither sugar nor alcohol! They are sweeteners which usually end in -ol, such as xylitol or sorbitol, and they’re actually good for your teeth.

What do fermentable carbohydrates do in the mouth?

Throughout the night and day, a soft, sticky biofilm called plaque forms on our teeth. It feels like a fuzzy coating.

Basically, the biofilm is a community made up of microbes who love to munch away on carbohydrates. The carbs help them reproduce so that over time, the biofilm is made up almost entirely of bacteria. And the longer they’re left to their own devices, the more species of bacteria join them. What’s worse, they tend to get nastier the longer things are left. That’s why removing them regularly is such a good idea!

Not all of the bacteria in the biofilm are harmful, but some most definitely are. The main culprit involved in tooth decay is called Streptococcus mutans, or S. mutans for short.

S. mutans excrete an acidic waste product called lactic acid when they are fed, and up to half an hour afterwards. The acid makes the outer layer (the enamel) of the tooth go soft.

The Stephan Curve

The Stephan Curve shows the timeline of this acid attack:

The Stephan Curve shows how the timeline of acid attacks, during which tooth decay can happen

After you’ve finished eating or drinking, it takes about 20 minutes until the biofilm pH returns from acidic to normal.

Don’t brush your teeth while the pH is still acidic and the tooth surface is soft – you don’t want to scratch it. Wait until it has hardened again.

The same goes for acidic liquids, regardless of whether they contain carbohydrates or not. Diet sodas on their own don’t cause tooth decay, but they can cause acid erosion.

The process of the tooth surface softening is called demineralisation, and the opposite process of the tooth surface hardening is called remineralisation.

The process of tooth demineralisation and remineralisation

If there are too many episodes of demineralisation, and not enough remineralisation, tooth decay can happen.

Which foods are best for teeth?

Most foods, even savoury ones, contain some sugars and starches. So to cut down on the frequency, the best thing to do is to eat sweets at mealtimes. The same goes for fizzy drinks.

Here are some more tips:

  1. Avoid boiled sweets – they stay in contact with the teeth for a long time. Try a sugar-free alternative containing Xylitol. Xylitol inhibits the growth of S. mutans.
  2. Be aware of hidden sugars. “No added sugar” doesn’t mean that a product is sugar-free. Pure fruit juice always contains sugar, as do “low”-sugar options such as Ribena.
  3. Soft drinks can be particularly bad for teeth because we tend to drink them over longer periods of time. Choose sugar-free diet versions instead if you can’t cut down on soft drinks.
  4. While diet soft drinks can’t cause tooth decay, they can cause acid erosion. So try to limit the amount of time they’re in contact with the teeth.
  5. If you like sweet tea or coffee, switch to sugar-free sweeteners. Some teas protect your teeth from decay, especially green and black teas. The same can’t be said for infusions, many of which are quite acidic. Tea and coffee by themselves don’t cause tooth decay.
  6. Water and milk are good choices.
  7. Fruits are very healthy, they’re not as sticky as some other sweet things and they help with saliva production. But they’re also acidic and contain sugars. So you shouldn’t eat them as a snack during Recovery Time (at least not on a regular basis).
  8. Tooth-friendly snacks include nuts, raw vegetables, cheese, tuna, no-sugar soy yoghurt, and eggs.
  9. Use sugar-free mints or chewing gum after meals. They make your mouth produce more saliva, which helps to cancel out the acid in your mouth.

A visual snack guide

Some snack foods are more likely to cause cavities than others, depending on whether they contain carbohydrates, how sticky they are, and how quickly they are consumed. Here is a handy snack guide from

Brushing and cleaning

Compared to diet, oral hygiene is a relatively minor factor when it comes to tooth decay.

But it is still a factor. The bacteria involved in tooth decay constantly form a biofilm (plaque) on the teeth. This biofilm needs to be disturbed on a regular basis so the bad bacteria don’t get out of hand. The current advice is:

  • Brush twice a day (last thing at night before going to sleep, and one other time during the day, for example before breakfast)
  • Clean between your teeth once a day with floss or interdental brushes (or both). In adults, cavities are particularly common in between teeth, where the toothbrush doesn’t reach, and you’ll need to use floss or interdental brushes (rather than a Waterpik) to disturb the biofilm.

Avoid brushing your teeth for half an hour after meals and sugary or acidic drinks. This prevents damage to the softened enamel. The advice to brush straight after every meal and after eating sweets is outdated.


Fluoride helps prevent tooth decay.3 It’s best to use a full-strength fluoride toothpaste (1350-1500ppm fluoride). If you don’t like the taste, read our page on toothpaste phobia for tips.

If you are at high risk of tooth decay, your dentist or dental therapist can prescribe a prescription-strength fluoride toothpaste (2800-5000ppm fluoride).

Toothpaste should be full-strength fluoride
Welcome to DFC – not a single product placement in sight! (thanks to

How to use toothpaste:

  • Use a pea-sized amount. Work the paste right into the bristles of the brush so that it doesn’t all fall off in a big lump when you put it into your mouth.
  • Spit out the toothpaste after brushing – don’t rinse! This allows the fluoride to stay on the teeth, rather than being washed straight off again. Spit out as much as possible and don’t worry about swallowing the rest. Brush just before heading off to bed for maximum effect.
  • If you want to use a fluoride-containing mouthwash as well, you can do so at other times of the day, in between brushing. The fluoride in mouthwash isn’t as effective as in toothpaste.

Dry Mouth

A dry mouth increases the risk of tooth decay. Saliva contains a number of elements, such as calcium, fluoride, bicarbonate and phosphate ions, which help to neutralise plaque acids. They also help to repair early tooth damage and decay.

Things that can cause dry mouth include:

  • certain medical conditions (especially Sjogren’s Syndrome)
  • certain drugs including tricyclic antidepressants, antispasmodics, some anti-psychotic drugs and HAART for people living with HIV
  • the menopause, or taking Hormone Replacement Therapy
  • radiation treatment
  • damage to the salivary glands

If dry mouth is becoming an issue, ask your doctor to prescribe you some artificial saliva. Make sure they prescribe one called “Saliva Orthana”, which also contains xylitol to protect against tooth decay. The default prescription from GPs is Glandosane which is nowhere near as good. 

Saliva Orthana is not suitable for vegetarians though, while Glandosane is. Another alternative is Biotene.

Saliva Orthana comes in a big bottle with a small spray bottle. You decant some into the spray bottle from the big bottle as required. Just give your mouth a spray when it feels too dry.

There are many products which can help with dry mouth. The main manufacturer (in the U.K. at least) is Biotene, but there are many artificial saliva products, lozenges, gels and sprays which may help. Ask your dentist or pharmacist for advice and recommendations. Make sure that any lozenges or boiled sweets you use to alleviate dry mouth are sugar-free.

If you’re on a medication that’s causing you dry mouth, check with your doctor if it can be changed.

It is important to keep sugary foods and drinks to mealtimes only. Your dentist may also want to prescribe a toothpaste with high fluoride content.

Avoid mouthwashes which contain alcohol, as these can dry out your mouth!

How is tooth decay treated?

It depends how deep it has gone into the tooth (see image below). 4

If it’s just in the outermost layer of the tooth (the enamel), you may be able to stop it from getting worse and harden up again (scroll down to find out more). Your dentist will be able to keep an eye on it during regular check-up appointments.

Tooth anatomy showing the enamel, dentine and pulp

If the decay has gone into the layer underneath (the dentine), it is treated by removing the parts of the tooth that have gone bad, and replacing the missing parts with a filling.

If it has gone further than the dentine and into the pulp (the innermost part of the tooth), you can often save the tooth with root canal treatment.

How to stop tooth decay in its tracks

If you cannot see a dentist yet due to fear or finances, you may ask yourself “Is it possible to reverse existing tooth decay?”

Surprisingly, the answer is yes. “Reverse” may be too strong a word because teeth can’t refill themselves and turn white again. But you can certainly stop existing decay, make it inactive, and make the tooth surface hard again. In the trade, this is known as “arrested decay”.

Two of our dentists explain exactly how it’s done:

Restrict carbs to mealtimes and use fluoride

Decay is a dynamic process, so far as we’re aware, the surface of teeth is constantly in a state of demineralising/remineralising. Decay happens when something tips the natural balance too far in the demineralising direction.

Since you need bacteria/fermentable carbohydrate/susceptible teeth all to be present for decay to progress, then changing the balance of one of the three will change the decay progression.

It’s not likely that you can alter the bacteria much, although obviously making sure that you’re cleaning the area thoroughly 3 times a day will help. Cut down the carbohydrates in your diet by restricting them to mealtimes and make the enamel less vulnerable to attack by getting lots of fluoride into it are the best way to deal with decay. The easiest way to do that is to get some fluoride toothpaste and when you’re finished brushing your teeth with it, rub it vigorously into the affected areas and DON’T rinse out afterwards. You can slosh about loads of fluoride mouthwash as well, but getting the paste in there is best. – Gordon Laurie, BDS

Change your diet and put cavities into hibernation

Having observed many apprehensive patients who may come and see me on and off for maybe 10 years before they gain the courage to have the treatment, I have noticed how effective a change in diet is at almost putting these cavities into hibernation. I sometimes wonder how much benefit they get by having them filled.

So my message to people in that situation is…

If you are reading this and you’re not yet ready to take the step and get treatment or even see a dentist, then I would say to you follow these steps and try to change your diet. I’m not talking a little bit on and off, I’m talking a full-on revolution because it can and does put even large cavities into hibernation. If you get it right, they will slow down so much you can buy yourself years of time. One thing to note is they will tend to go very dark in colour, changing from a tan colour to a tarry black. Don’t be alarmed, this means you have done it! – Lincoln Hirst, BDS

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Sources of Information and Footnotes

Lamont, R., & Jenkinson, H. (2010). Oral Microbiology at a Glance (1st ed.). John Wiley & Sons.

  1. Pitts, N., Twetman, S., Fisher, J. et al. Understanding dental caries as a non-communicable disease. Br Dent J 231, 749–753 (2021).[]
  2. Non-fermentable carbohydrates are carbohydrates or carbohydrate mixtures that do not lower plaque pH below 5.7 during and up to 30 minutes after their consumption. See FDA (Food and Drug Administration), 1996. Food Labeling: Health Claims; Sugar Alcohols and Dental Caries. Federal Register 61 FR 43433.[]
  3. Fluoride helps prevent tooth decay in 3 ways:

    1. It remineralises teeth. When teeth are exposed to an acidic environment of pH 5.5. or below, a process called de-mineralisation occurs. Minerals are leeched from the tooth, and this is what causes tooth decay. There is an opposite process called re-mineralisation (sort of like tooth decay in reverse), where minerals are deposited back onto areas where minerals have been lost. This is where fluoride comes in handy. Fluoride ions in your mouth (like from fluoridated drinking water, toothpaste or mouthwash) get deposited onto the surface of teeth in areas where demineralization has occurred. The fluoride ions attract other minerals (such as calcium) which were lost during the demineralisation process.
    2. Fluoride protects against decay. When fluoride replaces the kinds of minerals that were lost during the demineralisation process, it forms a new type of tooth mineral called fluorapatite that’s actually harder than the tooth was originally.
    3. Fluoride fights the bacteria that cause tooth decay. Fluoride makes it harder for bacteria to produce acid and cling to the teeth.


  4. staff (2014). Medical gallery of Blausen Medical 2014. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436[]