Dental decay happens when the enamel and dentine of a tooth become softened by acid attack, producing a cavity (hole).

Dental decay is caused by plaque acids that gradually dissolve away the enamel and dentine of the tooth to produce a cavity. Dental decay is the same as tooth decay and is also known as 'dental caries'. Decay damages your teeth and may lead to the tooth needing to be filled or even extracted.

Decay happens when sugars in food and drinks react with the bacteria in plaque, forming acids. Every time you eat or drink anything containing sugars, the bacteria reacts with it to form acid. These acids attack the teeth and start to dissolve the enamel.

The attacks can last for up to an hour after eating or drinking, before the natural salts in your saliva cause the enamel to 'remineralise' and harden again. It's not just sugars that are harmful: other types of carbohydrate foods and drinks react with the plaque and form acid.

(These are 'fermentable' carbohydrates such as the 'hidden sugars' that can be added to processed food, natural sugars like those found in fruit, and cooked starches.)

In the early stages of dental decay there are no symptoms, but your dentist may be able to spot an early cavity when they examine or x-ray your teeth. This is why you should visit your dentist regularly, as small cavities are much easier to treat than advanced decay.

Once the cavity has reached the dentine your tooth may become sensitive, particularly with sweet foods and drinks, and acidic or hot foods. As the decay gets near the dental pulp you may suffer from toothache. If the toothache is brought on by hot or sweet foods this may last for only a few seconds. As the decay gets closer to the dental pulp the pain may last longer and you may need to take painkillers - paracetamol or ibuprofen - to control the pain. You must visit your dentist immediately as the tooth is dying and you may develop a dental abscess if it is not treated.

Toothache is a sign that you should visit a dentist immediately, as it is a warning that something is wrong. If you don't do anything, this will usually make matters worse, and you may lose a tooth that could otherwise have been saved.

The biting surfaces of the teeth and the surfaces between the teeth arer most likely to decay, as food and plaque can become stuck in these areas.

If the decay is not too serious, the dentist will remove all the decay and restore the tooth with a filling. Sometimes the nerve in the middle of the tooth can be damaged. If so the dentist will need to carry out root canal treatment by removing the nerve and then restoring the tooth with a filling or a crown. If the tooth is so badly decayed that it cannot be restored, the only option may be to extract the tooth.

No. In the very early stages of decay, your dentist may apply a fluoride varnish onto the area. This can help stop further decay and help 'remineralise' the tooth. However, it is important to continue with good oral hygiene routine, using fluoride toothpaste to prevent further decay developing.

As the adult molars appear, and if the tooth is free of decay, a 'fissure sealant' can be used to protect the tooth. The sealant is a plastic coating that fills all the little crevices in the tooth surface, creating a flat surface that is easier to clean. This is called a 'pit and fissure sealant sealant'. Adults can also have this treatment if the teeth are free of decay.

The best way to prevent decay is by brushing your teeth thoroughly twice a day with fluoride toothpaste, making sure that you brush the inner, outer and biting surfaces of your teeth. Using dental floss, tape or interdent aids also helps remove plaque and food from between your teeth and gumline. These are areas a toothbrush can't reach.

Visit your dentist at least once a year, and have sugary and acidic food and drinks less often. Avoid snacking between meals as this limits the time your teeth are under attack from acids. Chewing sugar-free gum for ten minutes after a meal can help your mouth produce more saliva, which helps to neutralise any acids which have been formed.

Your dentist or hygienist will show you what areas you need to take most care of when cleaning. They will also show you how to brush and floss correctly.

Plaque is a thin, sticky film that keeps forming on your teeth. It contains many types of bacteria.

The pulp is the soft tissue which contains bloods vessels and nerves and is in the middle of the tooth.

Dentine lies under the enamel, forming most of the tooth and can be sensitive to pain. Dentine covers the central pulp of the tooth.

Enamel is the hard protective outer coating of the tooth and is the hardest part of the body. It does not contain any nerves or blood vessels and is not sensitive to pain.