What is tooth decay?

Decay – To rot or cause to rot as a result of bacterial, fungal, or chemical action; decompose

Dental decay or dental caries is a major health problem in most industrialised countries, affecting 60-90% of school children and the vast majority of adults (at some part in their lives).

Dental caries is caused by the action of acids on the enamel surface. Acid is produced when sugars in food or drink react with bacteria present in the dental biofilm (plaque) on the tooth surface. The drop in pH leads to loss of calcium and phosphate from the enamel, a process known as demineralisation. If process leads to a breakdown in enamel and bacteria are able to proliferate into the deeper tooth tissues, cavitation may then occur, leading to pulpal death and eventually abscess formation.

So, what can we do to help prevent against dental caries?

There are four main factors/conditions that are needed for dental caries to progress:

  • TIME




Firstly, let us spend a little time looking at how our mouth will naturally protect our teeth against caries, this will then enable us to understand how these factors play a role in the progression of dental caries. The big protector of teeth that naturally occurs is SALIVA. Saliva acts as a buffer, meaning it will try to regulate pH in the mouth. We know that the critical pH for demineralisation to occur is 5.5 (remember, lower the number, the more acidic the condition). When we eat/drink a sugar containing product the pH in our mouths will drop below this level for approximately 20 minutes, during this time the saliva is buffering the pH back to ‘safe levels’. If this drop in pH happens only a few times a day, the risk of caries should remain low. However, if the FREQUENCY of sugar intake is high throughout the day, the critical pH will be reached many times, in fact the pH may not rise to safe levels for a long period of time. It is during this time that demineralisation will occur, and therefore caries risk will be higher. We therefore advise patients to both keep sugar intake to a minimum, but to also keep the FREQUENCY of sugar intake as low as possible.


Ok, now let us look a little more closely at the role of plaque in caries progression. A good oral hygiene programme will result in less plaque in the mouth, there will be less plaque on tooth tissues and on the gums, and therefore fewer bacteria to use sugar to cause a drop in pH and demineralisation of enamel. The longer plaque is left on tooth tissue the more damaging it becomes, therefore we currently advise brushing teeth twice a day for at least 2 minutes, and using interproximal cleaning aids (at least once a day); ideally interproximal brushes should be used where possible. Using an antibacterial mouthwash at a different time to brushing, say after lunch, may also help reduce plaque levels during this time. Regular hygienist appointments will also help with plaque and tartar (calculus) removal, especially in areas that are difficult to access.


Further prevention of dental caries can be achieved by the use of fluoride containing products. Studies show that the use of fluoride helps prevent the progression of caries by helping to remineralise dental tissues (enamel). Fluoride use in the developing dentition has been shown to help strengthen enamel, enamel is chemically different where fluoride was present during development. This extra fluoride which is taken up by enamel means it is much more resistant to caries. Studies have also shown that it can affect the depth of fissures on premolars and molars (shallower fissures mean easier access, less susceptible tooth tissues, and therefore a lower caries risk). Current recommendations for fluoride levels in toothpaste are:


Children up to the age of 3 years: pea sized amount of fluoride containing toothpaste 1000ppm

3 years onwards: pea sized amount moving up to toothbrush sized over time of fluoride containing toothpaste 1350-1450 ppm


It is recommended that toothpaste should not be rinsed away with water following brushing, patients only need to spit out excess. This means topical action of fluoride is maximised, along with action of antibacterials present in the toothpaste.


There are numerous occasions where more fluoride may be recommended, including patients with a higher caries risk (active caries), dry mouth, wearing of orthodontic appliances (removable and fixed), sensitivity, exposed root surfaces, following operations on the head and neck. Please discuss this with your dentist if you have further questions. Topical fluoride can be applied to developing teeth and again this is something that can be discussed with you dentist or hygienist.


We have already briefly touched on susceptible tooth tissues in an earlier paragraph, however let’s revisit this again now. Unfortunately, bacteria are fantastic at sticking to teeth. As soon as you put your toothbrush down after brushing, plaque is beginning to form on tooth surfaces. So, realistically, all teeth are susceptible to caries. However, more susceptible surfaces are those that are difficult to access. The rough fissures of molars and premolars are very difficult to clean and this is one area in particular that needs to be closely monitored. Use of fluoride varnish on these surfaces and potential sealing of fissures can help prevent fissure caries. Areas in between teeth that are not regularly cleaned ie. with floss, interproximal brushes, are also more likely to demineralise – again as we’ve already discussed, if daily removal of plaque here is not performed, plaque will be left there for the TIME needed for demineralisation to occur. Areas around fillings, crowns, overhangs, crowded teeth, impacted teeth all pose a threat for an increased caries risk. It is therefore important that regular check ups are adhered to, along with regular hygiene appointments (at present 3-4 x yearly is recommended for most patients).

This is a very brief introduction into the world of dental caries. If you have any further questions regarding dental caries, its treatment, and prevention, please speak to your dentist or hygienist at Marshgate Dental Practice.


Nicholas McAulay BDS (Manchester) MJDF