Decay in molar tooth

Tooth Decay: The Causes, Symptoms and How To Fix It.


If you are suffering from tooth decay, you’re not alone. Around 2 billion people worldwide are living with decayed teeth, according to the World Health Organisation (WHO). In fact dental decay is the world’s most common health condition, the Global Burden of Disease report 2019 found.


What’s more, in 2010 WHO estimated that the worldwide cost of treating tooth decay was a staggering US$442 billion!


But decaying teeth are not a new phenomenon. Archaeologists have found tooth decay in the teeth of Neanderthal skulls dated 40000-22000 BC.


And the most amazing thing is that tooth decay is a preventable condition!


So what causes this widespread and expensive disease that’s been around for thousands of years?


What does it feel like when you have it?


And how can you prevent it or fix it?


What is tooth decay?


Tooth decay, is the phrase we use to describe damage to teeth. Today we know that the acid produced by bacteria in your mouth cause this damage.


But over the last four thousand years, scientists have suggested many causes of tooth decay. From the stagnation of depraved juices inside teeth to evil worms gnawing holes in them!


Disgustingly, Antonie van Leeuwenhoek, one of the first ever microbiologists, wrote that he took live tooth worms from the corrupt teeth of his wife. He commented that they were the same as living cheeses-worms that were found from a cheese shop!

Cartoon of worm coming out of a tooth

Tooth decay has also been called many different things. My particular favourites being dental gangrene and mortification! I wonder if people would be more bothered about having holes in their teeth if we called decay one of these more descriptive names?


Nowadays, dental decay or tooth decay are the terms commonly used. You may also hear your dentist refer to decay as dental caries. This was a term coined in the 1600’s and comes from the Latin meaning decay. Dentists use it routinely.


If you’re interested in finding out more about the history of tooth decay check out this article.


Causes of tooth decay


As early as 350 BC, the Greek philosopher Aristotle noticed that sweet foods such as figs and dates caused tooth decay. However, it wasn’t until 1500 years later that dentists pieced together the science behind it. That tooth decay was caused by the acid produced by bacteria when they feed on sugary foods.


There are millions of bacteria in your mouth. Incredibly there over 700 different types! As disgusting as that may sound, most of them are actually “good bacteria” and important for keeping your mouth healthy.

Unfortunately, like in every good story, from Star Wars to Harry Potter, there’s a dark side. The villains in your mouth are two bacteria called Streptococcus Mutans and Streptococcus Sorbrinus. These partners in crime live on the surface of your teeth in plaque.


Plaque is a sticky film that constantly forms on the surfaces of your teeth. You know that horrible fuzzy coating you can feel when you run your tongue over them?


The “bad” bacteria love acidic surroundings. So when you eat sugary, acidic and processed foods those guys have a party. They feed on these sugary foods and produce even more acid.


Looking at this picture of Streptococcus Mutans at really high magnification makes me wonder if perhaps good old Antonie van Leeuwenhoek wasn’t so wrong about the worms after all!

heavy deposits of dental plaque on teeth
Scanning electron microscope oftretococcus mutans: bacteria which cause tooth decay

Why is acid so bad for teeth?


Do you remember learning about pH at high school? If not you can check out this article for a refresher!


pH 7 is neutral and anything below that is acidic. When the pH of your mouth falls below 5.5, your teeth are in the acid danger zone.

pH scale showing pH5.5 as danger zone for acid attack for teeth

The enamel of your teeth is made up of a crystal structure of 2 minerals: calcium and phosphate. We call this hydroxyapatite.


Despite being the hardest substance in your body. when the pH of your mouth enters the pH 5.5 danger zone, the enamel hydroxyapatite starts to dissolve. This is known as demineralisation.


Fortunately, this process is reversible and remineralisation is possible. Once you’ve stopped eating, the pH in your mouth increases and the calcium and phosphate in saliva help the Hydroxyapatite to remineralise. This takes about 30 mins to an hour.

By limiting the amount of sugary foods you eat and reducing how often you eat them, you can help your mouth to recover from the acid attack and allow your teeth to remineralise. This means that demineralisation and remineralisation remain balanced and tooth decay doesn’t occur.



Scales showing balanced demineralisation and remineralisation and a healthy tooth

If you eat lots of sugary foods throughout the day or graze on sugary foods, then the acid environment becomes normal for your mouth. So the bad bacteria party on and produce more acid and remineralisation doesn’t occur.


This means that the enamel of your teeth is losing minerals. As time goes on you’ll start to see this in your mouth as a white spot, then grey shadowing under the surface of the tooth and eventually a hole or cavity.


Once a cavity has formed, there’s no going back. Remineralisation isn’t possible and your dentist has to remove the dental decay and fill the hole.

Stages of tooth decay


Tooth decay has 4 stages:


1. White spot lesion


The first sign of tooth decay is a chalky white spot. At this stage remineralisation is still possible. It’s a great idea to go and see your dentist if you’re worried about a white spot. They will give you advice and help you to try to reverse the demineralisation.

White spot lesion: earliest sign of tooth decay

2. Enamel Decay


Your tooth starts to decay in the enamel underneath the outside surface of your tooth. You may see a grey shadow on the tooth or staining in the grooves of your tooth.


If you’ve ever been to the dentist and they’ve told you that you need a filling and you’ve thought but there’s no hole in my tooth and it isn’t sore, trust their trained eye. They’ve seen enamel caries under the surface of your tooth in your mouth or they may have seen it on an x-ray.


By removing this decay they’ll prevent it from progressing further into the tooth and causing you toothache.


If left, once the enamel under the surface is decayed badly enough, the surface enamel will “cave-in” and that’s when you’ll first notice a hole in your tooth. A hole is not the first sign of tooth decay, it just might be the first sign that you see or feel.

Enamel decay in teeth

3. Dentine Decay


The dentine which lies below the enamel in your teeth is a much softer substance. Once decay has passed through the enamel it will spread into the dentine. You may start to feel more pain or sensitivity at this point. The risk of your tooth breaking also becomes more likely.

Tooth decay into dentine

4. Pulp Involvement


The pulp is in the centre of your tooth and is where we find the blood vessels and the nerves of the tooth. Progression of bacteria towards the pulp causes it to become irritated. You will experience more pain at this stage. This irritation of the pulp can be reversible or irreversible.


If it is reversible your dentist will be able to remove the decay and fill the hole in your tooth. If it has gone further and is irreversible, then the pulp has to be removed and the root of the tooth filled. This is called root canal treatment.


If the pulp becomes involved and you do not seek treatment from your dentist, pus can form in the tissues surrounding the tooth and this is when an abscess can start. The pain from this can often be constant and severe and you may find that you have swelling of your mouth or face. Eating will become very difficult.


Left untreated this infection can spread and can sometimes be life-threatening.

Girl with swollen face from tooth abscess


What does tooth decay feel like?


Tooth decay when it first begins in the enamel is often painless, decay will be happening but you will have no pain.


As the decay progresses through your tooth, you will initially experience sensitivity to cold, hot and sometimes sweet foods and drinks. This will then progress to more severe occasional pain, which often comes on by itself.


Once bacteria reaches the pulp and pus has formed in the tissues around the tooth, the pain will be constant, severe, throbbing and likely to keep you awake at night.


This is why it’s so important to see your dentist regularly. They can pick up early tooth decay that you may not even know you have, at a stage where it may be reversible. Once you are experiencing toothache, tooth decay is unlikely to be reversible.

Woman with toothache


Risk factors for tooth decay


You are much more likely to experience tooth decay if you:


  • Eat large amounts of sugary/acidic foods


  • Eat sugary/acidic foods regularly throughout the day


  • Don’t look after your teeth– removal of plaque is key to removing food debris and plaque


  • Don’t use fluoride – fluoride aids with remineralisation of enamel making it stronger

If you have any of the conditions below you are at higher risk of having tooth decay and you should visit your dentist more regularly:


  • Dry mouth (xerostomia) – saliva is so important in washing away food debris and remineralising enamel. If you suffer from a dry mouth you have less saliva, so it is even more important that you have excellent oral hygiene and a low sugar/acid diet. Some medicines and illnesses can cause dry mouth. If you have a dry mouth please don’t hesitate to ask your dentist for advice.


  • Eating disorders/acid reflux/alcoholism: regular vomiting or acid reflux increase the amount of acid in your mouth, causing your tooth enamel to be regularly bathed in acid.


  • Gum disease: gum disease causes shrinking back (recession) of your gums down your teeth, exposing the root surfaces. There is no enamel on the roots of your teeth, just dentine. As I’ve said this is much softer than enamel and is more easily attacked by the acids. This means tooth decay starts and progresses more readily on the roots of your teeth. Root caries (tooth decay on the roots of your teeth) is something we often see in older patients with gum disease.

Complications of tooth decay


Given that tooth decay is a preventable disease, the complications of it can be very debilitating.


You may experience:


  • Severe pain
  • Disturbed sleep
  • Inability to concentrate
  • Risk of tooth breaking
  • Difficulty eating
  • Bad breath
  • Swelling
  • Life threatening infection/sepsis


How to Prevent Tooth Decay


Fortunately, we’ve moved on from the 11th century cures of charms and herbal remedies for toothache. We are so lucky that we are now confident about the cause of toothache. This means we know what you can do to prevent it. Here’s what you need to do to prevent tooth decay:


1. Have good oral hygiene


In the mid 1800s, American dentist Levi Spear Parmly became the first dentist to recommend oral hygiene for the prevention of tooth decay. In his first book he wrote:

“The first and most important object from Childhood is the cleanliness of the Teeth. . . . Though we should be careful to clean the teeth after every meal, it is more particularly necessary before retiring to rest; the foulness which has been all day accumulating, is thus prevented from committing its ravages during the night.”

Levi Spear Parmly

This guy was way before his time!


So what is oral hygiene?


  • Brush your teeth twice a day


Once before bed at night and once at another time of day


At breakfast time if you eat or drink something acidic like fruit juice, wait 30 minutes to an hour before brushing your teeth. If you don’t have time for that, brush your teeth before breakfast.


Brushing too quickly after having something acidic can do more harm than good and brush away the dissolved minerals from enamel.


Regularly brushing your teeth removes the food debris that the bacterial partners in crime streptococcus mutans and streptococcus sobrinus love so much. Brushing removes the plaque too which means you are also removing the bacteria that’s stuck to your teeth.


Watch our hygienist, Laura, in the video below show you how to brush your teeth like a hygienist and also how to use interdental brushes.

  • Use a fluoride toothpaste (check the label – it should say 1450ppmF)


Do you remember I said that enamel is the hardest structure in the body and is made of calcium and phosphate minerals, known as hydroxyapatite. If fluoride is present in your saliva when the enamel remineralises it is taken up into the hydroxyapatite and actually makes it even stronger and more resistant to decay.


  • Don’t rinse after brushing


The fluoride and antibacterials in toothpaste are really useful and we want to keep them in your mouth for as long as possible. Rinsing with water washes these away, so don’t do it!


  • Interdental cleaning


Each tooth in your mouth has 5 surfaces, so if you think about it, brushing only cleans 3 of them. Plaque doesn’t just stick to the front, back and biting surface of your teeth, it’s inbetween them too.


Cleaning between your teeth with floss or interdental brushes is just as important as brushing them. According to the Oral Health Foundation, flossing before brushing is the best way to do it. 

2. Eat a balanced, low-in-sugar diet


If we believe the history books, we’ve known for more than 1500 years that sugary foods cause tooth decay. Unfortunately, processed high sugar foods are now much more readily available than they were in Aristotle’s time – he was just worried about dates and figs!


The reality is that sugar has no nutritional value. There is actually no need for us to have sugar in our diets. However, I’m a realist. Sugar is yummy and it makes us feel good. That means though we should view it as a treat and only have it occasionally.


This infographic shows the NHS recommendations for the maximum amount of sugar you should eat a day. These are based on the WHO advice that the amount of free sugars that you eat should be to less than 10% of your total energy intake, as this study shows.


According to the NHS “free” sugars are

  • Any sugars added to food or drinks. These include sugars in biscuits, chocolate, flavoured yoghurts, breakfast cereals and fizzy drinks. These sugars may be added at home, or by a chef or other food manufacturer.


  • Sugars in honey, syrups (such as maple, agave and golden), nectars (such as blossom), and unsweetened fruit juices, vegetable juices and smoothies. The sugars in these foods occur naturally but still count as free sugars.


This is a great NHS resource to learn more about sugar and how to reduce how much you eat



How Much Sugar Should I have infographic

If you do have to have something sweet here’s a few key points to remember:


  • Avoid sticky things – “bad” bacteria love them because they hang around and they’re hard to remove


  • Enjoy sweet treats or drinks with a meal and brush your teeth half an hour to an hour afterwards. on sweet things or sipping on juice never allows your mouth to recover from the acid attack. You’re providing a constant source of acid for the “bad” bacteria to party with. 


  • Drink water with sweets to wash away any debris.


  • Use straws with soft drinks to keep them away from your teeth


If you have children:


Remember children don’t need to have sweet things, the longer you can keep them away from sweet treats and fizzy drinks the better. Don’t worry, you are not depriving them, you’re keeping them healthy.


We also often see distressed parents of babies or toddlers with decay in many of their baby teeth, as a result of having bottles of juice or even milk in bed overnight with them.


This allows them sip continuously and means their teeth are constantly bathed in acid. Don’t forget even milk contains sugar and although it’s good for you constant sipping for hours overnight will cause severe tooth decay that can look like this.

Early childhood tooth decay


How to fix tooth decay


We can reverse the earliest signs of tooth decay, as I’ve said. This can be done with good oral hygiene and fluoride. Your dentist may prescribe a high-fluoride toothpaste or may apply a high-concentration fluoride gel to very early decay.


Once there is a hole in your tooth, your dentist needs to remove the decay and infected parts of the enamel and dentine,  and place a filling.

If the decay is extensive and you have lost a lot of your tooth, you may need a crown.


Once the pulp is involved, root canal treatment or extraction are the only treatments available to deal with your decay.


These pictures show early decay, spotted by the dentist, removed and filled with a tooth-coloured filling material.  The tooth looks good-as-knew, the patient had no toothache and the decay has been removed so cannot spread further.

Tooth with tooth decay being repaired with a filling



Tooth decay has been around for thousands of years. In the past our ancestors didn’t know what caused it and therefore couldn’t treat it or prevent it.


We are in the privileged position of knowing what tooth decay is, what causes it and how to prevent it.


With good oral hygiene and a balanced low-in-sugar diet you can easily avoid the suffering that tooth decay can cause.


If you’re worried that you may have tooth decay please don’t hesitate to contact us. Remember, dentists are experts in seeing tooth decay and if we catch it early enough we can help you to reverse it or fix it before it causes you pain.


Blog post written on 28th April 2022

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