Dental caries - Causes of tooth decay

Tooth decay occurs when a sticky acidic film called plaque builds up on your teeth and begins break down the surface of your teeth.

How tooth decay develops

Your mouth is full of bacteria, which combine with small food particles and saliva to form plaque.

When you consume food and drink high in carbohydrates – particularly sugary foods and drinks – the bacteria in plaque turn the carbohydrates into energy they need, producing acid at the same time.

Regularly cleaning your teeth can remove plaque, but if it's allowed to build up, it can begin to break down the surface of your tooth.

The plaque will first start to soften the enamel (the hard outer coating of a tooth) by removing minerals from the tooth. Over time, a small hole known as a cavity can develop on the surface. This will cause toothache.

Once cavities have formed in the enamel, the plaque and bacteria can reach the dentine (the softer, bone-like material underneath the enamel). As the dentine is softer than the enamel, the process of tooth decay speeds up.

Without treatment, plaque and bacteria will enter the pulp (the soft centre of the tooth that contains nerves and blood vessels). At this stage, your nerves will be exposed to bacteria, making your tooth very painful. The bacteria can also infect tissue within the pulp, causing a dental abscess.

Tooth decay typically occurs in teeth at the back of your mouth, known as molars and premolars. These are large flat teeth used to chew food. Due to their size and shape, it is easy for particles of food to get stuck on and in between these teeth. They are also harder to clean properly.

It is more common for a front tooth to be affected by tooth decay when it is touching another tooth alongside it.

Increased risk

There are a number of factors that can increase your risk of tooth decay. These include:

Diet

Eating food and drink high in carbohydrates, particularly snacking regularly between meals, will increase your risk of tooth decay.

Tooth decay is often associated with sweet and sticky food and drink – such as chocolate, sweets, sugar and fizzy drinks – but starchy foods – such as crisps, white bread, pretzels and biscuits – also contain high levels of carbohydrates.

Some medications can also contain sugar, so it's best to use sugar-free alternatives whenever possible.

Poor oral hygiene

If you do not regularly brush your teeth and clean between them with floss or an interdental brush, you are at a higher risk of tooth decay. You should brush your teeth at least twice a day using fluoride toothpaste.

Read more about how to keep your teeth clean.

Smoking and alcohol

People who smoke and drink alcohol regularly are at an increased risk of tooth decay.

This is because tobacco can interfere with production of saliva, which helps keep the surface of your teeth clean, and alcohol can contribute to the erosion of tooth enamel.

Dry mouth

People who have lower levels of saliva in their mouth are at higher risk of developing tooth decay, because saliva helps to keep the surface of your teeth clean and can neutralise acids in your mouth.

A number of medicines, medical treatments and health conditions can lower the amount of saliva in your mouth, including:

• tricyclic antidepressants (TCAs)
• antihistamines
• some antiepileptic medicines
• some antipsychotic medicines
• beta-blockers
• radiotherapy 
• Sjogren's syndrome – a condition where the body’s immune system attacks glands that secrete fluid, such as the tear and saliva glands

If you are taking a medicine, receiving treatment, or have a medical condition known to cause dry mouth, it's particularly important to maintain good oral hygiene and ensure you stay well hydrated.

Read more about preventing tooth decay for tips on how to keep your teeth healthy.