Dental Professionals
Science focussed. Patient focussed.
Science focussed. Patient focussed.

What is Tooth Decay?

Tooth decay, or caries, is one of the most common dental conditions.1 Bacteria found in dental plaque secrete acids which break down the mineral structure of enamel, a process known as demineralisation. Ultimately this bacterial attack can corrode right through the enamel (or cementum) and underlying dentine to the dental pulp, damaging or destroying the internal structure of the tooth.

Plaque bacteria can accumulate above and below the gum line. If left to build up, subgingival plaque can cause the gum margin to pull away from the teeth, creating pockets through which bacteria can enter2 and attack the more vulnerable part of the tooth within the gums. Teeth are more susceptible to decay below the gum margin,3 so it is important to remove as much plaque as possible from the gums during tooth cleaning in order to maintain a tight, healthy gum line.

Tooth enamel becomes vulnerable to dissolving below a pH of around 5.4.It’s important to note that it is dietary sugars, not dietary acids, which cause caries, although the latter can lead to erosive tooth wear. Plaque bacteria metabolise sugars to produce acids, which in turn cause a localised demineralisation of enamel.

The bacterial conversion of sugars to acids occurs quickly following sugar ingestion. This “acid attack” induces a rapid drop in plaque pH levels, causing temporary demineralisation of the tooth surface. It can take between 20 minutes and 2 hours for saliva to dilute the acid, restore plaque to a neutral pH level and remineralise the teeth – if more sugars are consumed during this time, further demineralisation may occur while the teeth are already vulnerable, increasing the likelihood that caries will develop.5  

Once sufficient dissolution of tooth mineral has occurred, the remaining organic tissue, unsupported, is lost, resulting in a cavity.

What increases the risk of tooth decay?

  • Sugars are key in the production of bacterial acid, so those with a diet high in sugars are naturally at an increased caries risk
  • Poor oral hygiene practices resulting in the accumulation of plaque can also increase the risk, due to increased levels of acidogenic bacteria
  • Those suffering from dry mouth are at a greater risk of caries, since saliva has important roles both as an antimicrobial agent and in buffering oral pH6,7
  • Since fluoride is a potent anti-caries agent, failure to use a fluoridated dentifrice increases the risk of caries.


1. J Murray. In: JJ Murray, JH Nunn & JG Steele (Eds). Prevention of Oral Disease: Fourth Edition, pp3-5. Oxford: Oxford University Press, 2003.

2. V Clerehugh et al. In: V Clerehugh, A Tugnait & RJ Genco (Eds). Periodontology at a Glance, pp16-17. Oxford: Wiley-Blackwell, 2009.

3. Shaker RE. Saudi Dental Journal 2004; 16 (2): 84-92.

4. Hoppenbrouwers PMM et al. Archives of Oral Biology 1987; 32 (5): 319-322.

5. RS Levine & CR Stillman-Lowe (Eds). The Scientific Basis of Oral Health Education: Sixth Edition. London: BDJ Books, 2009.

6. Guggenheimer J & Moore PA. Journal of the American Dental Association 2003; 134: 61-69.

7. Tenovuo J. Journal of Dental Research 2002; 81: 807-809.


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