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 January 17, 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 2 minutes, ideally before breakfast and before going to bed. Use an electric toothbrush and toothpaste containing 1350-1500ppm fluoride. Spit out the toothpaste and don’t rinse.
  3. Clean between teeth (using interdental brushes or floss) once a day.

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

What is tooth decay, and what causes it?

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 fermentable1.

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.

The biofilm is a community made up of microbes. Like a game of Settlers, it goes through several stages:

  • A clean tooth surface, when exposed to saliva, will almost immediately become coated by a thin protein film. This film acts as a glue.
  • The first bacteria (early colonisers) attach to the sticky surface, colonise it, and continue to grow 2.
  • When left to grow for a while, the biofilm will become more attractive to other bacteria (late colonisers), who join the party.

Fermentable carbohydrates don’t just provide us with food, but also the bacteria in the biofilm, who love to munch away on them. The carbs help them reproduce, so that over time, the biofilm is made up almost entirely from bacteria.

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 (lactic acid) when being fed, and up to half an hour afterwards. The acid makes the hard tissues of the tooth go soft. This can result in decay if it happens too many times each day.

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

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

How can tooth decay be prevented?

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 sweet or starchy things.

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.

This is how I advise my patients. I like to keep it simple and easily understandable. We call this method ‘Fair Play To You And Your Teeth’ because you get what you want and your teeth get what they want! It is fair and even-handed. – Philip Christie (M.Dent.Sc.)

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.

Which foods are best for teeth?

Most foods, even savoury ones, contain some sugars and starches. So the best thing to do is to eat sweets at mealtimes (as a dessert) to cut down on the frequency. 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 you should 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, some of which are quite acidic. Tea and coffee by themselves don’t cause tooth decay.
  6. Water and milk are good choices.
  7. Fruit 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 the Recovery Time (at least not on a regular basis).
  8. Sugar-free snacks include nuts, raw vegetables, cheese, tuna or 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 (ideally before breakfast and last thing at night before going to sleep)
  • Clean between your teeth once a day (using either floss or interdental brushes). In adults, cavities are particularly common in between teeth, where the toothbrush doesn’t reach, and you’ll need floss or interdental brushes 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

  1. 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.[]
  2. These “early pioneers” include Streptococcus sanguis, Streptococcus oralis, Streptococcus gordonii, and Streptococcus mitis, swiftly followed by lactobacilli and S. Mutans[]
  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[]