Tooth decay

Also known as holes, cavities or caries

Tooth decay is damage that occurs when a combination of bacteria, plaque and acids in our mouth eat away at a tooth. This can lead to a 'hole' in the tooth, known as a cavity or caries.

The saliva in our mouths has anti-cavity properties of that can help protect our teeth to some extent. Unfortunately, our modern diets and easy access to sugar encourages the growth of bacteria and this has led to an increase in tooth decay. At best unsightly, tooth decay can cause pain, infection and – in rare cases – death.

Causes of tooth decay

Bacteria feeds on sugar

Bacteria and sugar work together to cause tooth decay, and our battle against it is being lost largely due to our modern diets of sticky, high-sugar foods and drinks – particularly if these are consumed between meals.

Bacteria feeds on the sugars in our diet (sucrose, glucose, fructose in fruits) and forms plaque – a sticky bacterial slime which coats the teeth.

Saliva can't compete

Saliva works hard to combat this erosion. It washes food debris away and contains an acid-neutralising buffer as well as minerals to rebuild the tooth. But the frequent high-sugar snacks that many people eat during the day create a constant supply of ammunition for the bacteria sitting on our teeth, and the saliva simply cannot compete.

Cavities develop

The cavity that develops in the tooth enamel allows bacteria and acid to gain access to the sensitive inner layers of the tooth – the dentine and, below that, the pulp. The pulp contains the nerves of supplying the tooth. The longer it is left untreated, the more advanced the decay becomes.

Plaque acids corrode

If not removed while it is soft, plaque hardens and becomes difficult to remove. Plaque produces acid as a by-product which erodes the protective outer layer of enamel.

Plaque and tartar provide the ideal environment in which bacteria thrive, causing gum disease and tooth decay. Keeping plaque and tartar at bay with good dental hygiene is key to oral health.

Symptoms of tooth decay

When the hard, outer layer of tooth enamel develops a hole, bacteria and acids get access to the more sensitive layers beneath – the dentine and pulp. This can cause pain and make your tooth vulnerable to further decay and infection. The following signs and symptoms suggest you may have a dental cavity:

  • a white mark on the surface of a tooth – suggests very early development of a cavity
  • a brown spot – suggests a cavity in the later stages of development
  • a dark spot that becomes larger and soft to touch – as the cavity becomes more noticeable
  • pain – a later symptom of tooth decay (pain may be constant or only when you eat or drink foods that are hot, cold or sweet)
  • bad breath and foul tastes – also suggest you may have a dental cavity.

Treatment of tooth decay

You should see your dentist regularly to prevent dental problems or spot them early. If you suspect you have a tooth cavity, visit your dentist as soon as possible. The sooner you address it, the more effective the treatment will be.

Treatment of dental cavities can involve:

  • application of fluoride to reverse minor enamel damage
  • removing the decayed part of the tooth and filling the hole (with either an amalgam, gold or white filling)
  • removing (extracting) the whole tooth if it can’t be saved
  • removing a large part of the tooth and replacing it with a tooth-shaped crown
  • a root canal filling – if the tooth pulp has died as a result of infection from the cavity, the tooth can often be saved this way.

If untreated, a dental cavity can lead to infection in the surrounding gum (gingivitis) or sinuses. Some of these secondary infections can be serious, or even life-threatening.

Preventing tooth decay

Good oral care and a healthy balanced diet with foods containing calcium (milk products and vegetables), fluoride (fluoridated water, seafood, tea, gelatin) and phosphate (leafy vegetables, fruit, meat and poultry) are essential in the prevention of cavities. The following tips may also help in reducing the risk of cavities.

  • Brush your teeth twice a day (especially last thing at night before going to bed) using a fluoride toothpaste.
  • Floss between all of your teeth at least three times a week, and preferably chew sugar-free gum each day.
  • Visit your dentist or hygienist regularly (every 12 months).
  • Avoid sticky, sugary snacks between meals.
  • Minimise sugar in your diet.
  • Drink water and sugar-free drinks.
  • Avoid fizzy drinks – even diet soft drinks are acidic and can erode the teeth. 
Credits: Reviewed by Drs Geoffrey Tompkins and Alison Meldrun, School of Dentistry, Otago University. Reviewed By: Health Navigator Editorial Team