A Guide To Tooth Decay

This page will introduce you to the problem of tooth decay.  In particular we’ll provide a summary of the main causes of this dental disease, including those you will probably know and some surprises!

There is also a low-down on symptoms and different types of cavities.

We will then lead on to the prevention and treatment of decay.


Cavity Causes: The Obvious and the Sneaks

What is dental decay? – Also known as dental caries, or simply cavities, is the destruction of teeth caused by plaque acids.

"Graphic showing factors that are the causes of tooth decay"

The joint causes of tooth decay

There are two main tooth decay causes:

  1. Certain types of bacteria which are found in dental plaque. Plaque is that thin, white film that is constantly forming on your teeth after you brush (if you haven’t brushed in a few hours- scrape them with a fingernail and see what comes off). When these bacteria feed, they produce a harmful acid which erodes and destroys the tooth structure and can lead to cavities. So bacterial infection lies at the heart at the process. It also causes gingivitis. But to rot, it also needs…
  2. Food (and drinks).  In particular, the main dangers are sugars and carbohydrates.  Plaque bacteria love these.  They feed on the sugars/carbs and which they then turn into plaque acids.

So as soon as we eat certain foods our teeth are under attack from plaque bacteria.  This attack can last for at least an hour, until the saliva helps neutralize the acids.  Therefore the more often we eat these foods; the higher the percentage of the day the teeth are under attack.  The FREQUENCY of taking these harmful foods and drinks is more important than the actual amount consumed in terms of preventing tooth decay.


Decay occurs on different areas of a tooth

Your teeth are more prone to rot in areas where there is more plaque build-up. These areas include:

  • Grooves, pits or fissures.  These are natural indentations on the surfaces that are hard to clean.  Fissures in particular can be deep on the biting surfaces of molars and premolars.
  • The surfaces between teeth – ‘interdental’ spaces.
  • Near the gum line, in particular where there is any gum disease or recession.
  • Around fillings, crowns, partial dentures or bridgework.


Particular foods bring higher risks:

Obvious/well known causes:

"Image of candy/sweets"

Candy is a key offender!

  • Candy/sweets
  • Chocolate
  • Fizzy drinks and fruit juices
  • Biscuits/cookies
  • Ice cream
  • Jam/jelly

Less well-known causes of cavities (the sneaks):

Lots of foods are broken down in to sugars in the mouth

  • Fruits
  • Potato chips/crisps
  • Breakfast cereals
  • Pretzels
  • Yogurts

So it is not just well known foods that are bad for your teeth!!  There are lots of ‘hidden’ sugars in food and seemingly healthy carbohydrates are broken down into harmful sugars in the mouth.

There is a lot more advice and tips on foods that cause cavities, as well as the dangers of snacking in our diet and teeth section.


Dental Caries: The Process and Types

 “How does a cavity develop and spread?”

"Graphic showing three stages of tooth decay"

Three stages of dental decay, from minor to major damage! Click on image to enlarge.

Decay is a gradual process that follows a well-recognized pattern if it is left untreated:

  1. The acid erodes the tooth enamel just under the surface in a small area that is hard to detect.  A small white spot may be visible.  At this stage, reversing the damage is still possible.
  2. The damage continues through the enamel until it reaches the softer dentine. At this stage it can be said that a true cavity has formed. It can then ‘mushroom’ out rather quickly, destroying the dentine.  A lot of the structure can rot away without one knowing as the hard enamel can stay intact.  Once decay reaches the dentin, the damage done is permanent and will only progress.
  3. The decay will eventually reach the dental pulp where the nerve lies. Root canal or tooth extraction will be needed.


Check out the video or see these pictures for more on the process.


Although all decay of teeth has the same underlying cause, there are particular scenarios where it is more likely:

  • In young childhood, the teeth can be destroyed by ‘baby bottle’ decay.  As the name suggests, it is caused by a child being given a bottle (of milk or juice) to sleep with.  This type causes rampant destruction of the baby teeth, especially if they are not being cleaned properly by the parent. For more advice on dental health for children see here.
  • In our later years, we become more at risk of caries on the exposed surfaces of the roots of teeth; ‘root caries’.  The roots are more likely to become exposed as one gets older due to gum disease, gum recession and abrasion (over-brushing).  As roots have no overlying protective enamel they are more susceptible to disease.
  • Dry mouth is also more likely as one gets older.  Dry mouth (xerostomia) is a reduction in the flow of saliva.  As saliva normally helps protect the teeth, any reduction in flow will put them at more risk of disease.


"Decay Under Filling"

Cavity Under a Filling: Replacing this filling sooner would have stopped this spreading.

Cavities can also form underneath or around any dental work that has been placed.  For example:

  • Underneath fillings (see photo).  A particular risk is if a filling breaks but remains in place, so trapping plaque and food.
  • Around crowns and bridges, particularly if they do not fit properly or become loose.
  • Around orthodontic braces and retainers.
  • Underneath partial dentures.


Tooth Decay Symptoms

In the early stages, there are no symptoms!  This is a crucial point!

It is a key reason why you should attend the dentist for regular check-ups; so they can find any disease that you may not be aware of.  It is much better to find and treat cavities as early as possible!

"Image of a dental x-ray with tooth decay"

Image of a dental x-ray with severe damage

Once dental caries reaches the dentin, there may be sensitivity to cold, hot and sweet foods/drinks.

However, it is often not until the rot has advanced deep into the tooth and caused a large degree of destruction that it causes problems.  At this stage, the tooth may break as the shell of hard enamel gives way due to the dentine underneath being rotten.

Toothache will occur once the dental caries gets near the nerve, or ‘pulp’.  This tooth pain may begin as sensitivity only.  However, if left untreated it can progress to severe pain as the nerve begins to die off. This pain is typically worse at night, brought on by hot food/drink more than cold and it lingers for a long time after the heat is gone. Infection/abscess formation is often the end result if treatment is not sought.

Toothache is a sign that there is damage to the tooth – it must not be ignored. Visit your dentist immediately. Any delay may result in it rotting beyond repair.

For further reading see our page on cavity symptoms.



There are two main contributing factors that cause cavities: plaque bacteria and the foodstuffs we eat/drink. There are also situations both in terms of life-stages and the condition of our teeth/mouth that can put us at increased risk of disease.

As tooth decay often is ‘silent’ (you are not aware of it) until it has done a lot of tooth damage. Visit your dentist regularly and get treatment when needed.

Prevention and tooth decay treatment are outlined for you on the following pages.

Adult tooth decay rates

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