Tooth decay: Take the acid test

Decay isn't the only threat to our molars and incisors. Dentists are now fighting tooth erosion, caused by fizzy drinks and fruit – and the damage begins in childhood. Steve Connor reports

(Rex)

Most parents realise the importance of regular brushing to prevent tooth decay, but few are really aware of another serious and growing problem of dental hygiene. Tooth erosion caused by acidic food and drinks, and the resulting rise in the number of people suffering from sensitive teeth, is affecting an increasing proportion of the population. And it starts in childhood.

Anecdotal reports from dentists' surgeries suggest that tooth erosion resulting from the outer enamel being dissolved by acids in the mouth is an increasing problem. Data from the last survey of children's dental health, involving detailed examinations of more than 10,000 children, found a small but significant increase in erosion between 1993 and 2003. It also found that tooth erosion in the permanent – adult – teeth affects more children as they get older.

The mouth is a naturally non-acidic environment. Healthy saliva is neutral or slightly alkaline, which is at the opposite end of the spectrum to acidity. Acid and alkaline are measured on a logarithmic scale of "pH" running from 1, which is very acidic, to 14, which is intensely alkaline, with a pH of 7 being "neutral".

Saliva in a healthy mouth is about pH 7.4. However, some carbonated soft drinks have a pH as low as 3.4, making them highly acidic from a biological perspective. Acids erode the surface of teeth, which are essentially composed of calcium salts that are highly vulnerable to acidic attack. Indeed, if a tooth is dropped into a glass of fizzy drink, the enamel will eventually dissolve.

Tooth erosion can also have other causes. Nearly one in 10 people for instance suffer from gastro-oesophageal reflux, when the natural acids in the stomach flow up to the mouth. These stomach acids tend to erode the back teeth more than those at the front. Frequent vomiting associated with eating disorders and even over-brushing with abrasive toothpastes can also cause surface wear and erosion of the outer enamel that protects the tooth.

One of the common outcomes of erosion is painfully sensitive teeth. The thinning of the enamel begins to expose the inner, softer layer of dentine. One of the features of dentine is that it has microscopic channels or tubules that radiate out from the central pulp core to the outer enamel. It is these tubules that allow differences in temperature or sweetness to pass directly to the nerve, causing the sensation of pain.

"When teeth are alive they have pulp tissue inside, often called 'the nerve'. This is like any other living part of the body, with blood vessels, cells and nerves which penetrate into the dentine," says Keith Cohen, based at Dentexel, a practice in London, and one of the capital's best restorative dentists. "When a patient suffers from erosion, there is a gradual loss of enamel, exposing the dentine. Consequently, there is less protection of the nerve tissue and opening of the dentine tubules, resulting in sensitivity to various stimuli such as cold and hot, brushing, and foods that are erosive or sweet," he explains.

Dentists recognise two important causes of what they call "tooth-surface loss".

One is the chemical erosion of the surface by such things as dietary acids. This is quite different from the erosion caused by tooth decay resulting from the bacteria responsible for dental caries. Another major cause of dental erosion is physical wear, either resulting from to tooth-to-tooth "grinding" contact, or due to abrasion, such as from vigorous tooth brushing.

Tony Smith, professor of oral biology at The University of Birmingham, points out that these different elements can sometimes interact with devastating consequences. For instance, it is now well established that brushing the teeth soon after drinking an acidic drink, such as a fruit juice in the morning, can have a far more detrimental impact in terms of loss of enamel than either activity has on its own.

"An acidic drink can pre-soften the enamel and make it more susceptible to being abraded away as a result of heavy brushing. It can take up to 20 minutes for the surface of a tooth to get back to normal pH after an acidic drink. I advise people to wait 40 minutes or an hour after having acidic food or drinks before they brush their teeth," Professor Smith says.

This is why it's a good idea to brush your teeth in the morning before having a fruit juice for breakfast. It lowers the risk that chemical erosion and physical abrasion can work together to rub away the protective enamel surface.

Professor Smith says it is difficult to quantify the scale of dental erosion in the population and to gauge just how much worse the situation may be getting.

To do that, it would be necessary to monitor and examine a large group of children and young adults over many years, or have very large, regular surveys of the general population involving many thousands of people.

The dental health survey of children in 2003 from a wide mix of social backgrounds found that tooth surface loss on the "lingual" side of teeth (next to the tongue) of 12-year-olds increased from about 21 or 22 per cent in 1993 to about 24 or 26 per cent in 2003. For the buccal (next to the cheek) side, the respective increase was from about 6 or 8 per cent to 8 or 10 per cent. For 15-year-olds, the situation was worse, with lingual-surface erosion growing from 23 per cent in 2003 to about 26 or 28 per cent in 2003.

So it seems that tooth erosion has over the past 10 years has become more of a problem judging by this limited survey. It also gets worse as children get older, as the data on 15-year-olds show.

The fact that the inner, lingual side of the tooth is hit hardest also suggests that the cause could be chemical erosion rather than over brushing, although tongue movements across the softened tooth surface may also exacerbate the wear on this side of the tooth, according to Professor Smith.

One possible cultural explanation for the rise in tooth erosion is the move away in recent years from selling soft drinks in cans to serving them in plastic bottles with screw tops. This has encouraged the adolescent habit of sipping drinks throughout the day.

Professor Smith points out that children today are more likely to be taking constant swigs from a plastic bottle of fizzy drink rather than gulping the whole thing in one go (as they are more likely to do with a canned drink). "A bottle with a screw-top allows someone to carry it around with them and drink more slowly, constantly topping up the acidity of the mouth. The surface of the teeth keeps acidic for longer periods," Professor Smith says.

Whereas classical dental practice has in the past been directed at treating decay caused by dental caries, the modern problem of tooth erosion is more difficult to treat because it affects the entire surface of a tooth. Drilling and filling a tooth cavity is relatively easier to deal with than treating the entire surface of a tooth.

Cohen says that the first stage in treatment is to identify the cause of the problem – whether it is dietary or an underlying medical problem. He says that sugar-free chewing gum, which increases the flow of saliva, can help, as can finishing a meal with cheese or milk, which can neutralise salivary acid.

Sensitive teeth can be treated with high- fluoride toothpaste or remineralising pastes containing calcium and phosphate. Colgate, for instance, has recently released a desensitising toothpaste containing the amino-acid arginine and an insoluble calcium agent, which is "clinically proven" to fill the microscopic channels in the dentine that transmit painful stimuli in sensitive teeth.

Colgate reckons that hypersensitivity affects more than half of all dental patients worldwide and that its toothpaste poses a radical solution in that it literally plugs the problem, rather than simply treating the symptoms by numbing the pain of sensitive teeth, as other brands of toothpaste try to do.

But if the erosive damage is already done, restorative dentistry may be the only option. Cohen says that the treatments include: crowns, where the entire top of the tooth is reduced by about 1 millimetre and replaced with an artificial tooth; veneers, where the one surface, usually the front, is replaced by an artificial coating tailor-made in the lab for each patient; and composite coverings applied in the surgery. These last are cheaper than veneers and more easily repaired and modified, but can only be reliably dealt with by highly skilled professionals.

All of these solutions have their own drawbacks. Crowns, for instance, rely on a good tooth structure to act as a peg, and expensive veneers, which are good aesthetically, can work loose and chip. Composite coverings can stain if someone smokes or drinks lots of strong tea or red wine and may have a shorter lifetime than veneers or crowns. But none of them comes cheap.

The only real solutions to dental erosion are prevention and the avoidance of frequent contact between the teeth and acidic drinks and foods. That also means recognising the problem early enough in life to make sure it doesn't happen – which can be quite difficult when sipping fizzy drinks from plastic bottles is such a popular pastime among children and adolescents.

How to protect your teeth

* Drinks to avoid are fizzy, carbonated drinks, especially the colas (which contain phosphoric acid), pure fruit juice, and some alcoholic drinks, eg white wine and cider. Sparkling mineral water has minimal erosive effect.

* Foods to go easy on include fruits, especially citrus, grapes and sour apples. Beware also of sauces such as ketchup and brown sauce, and snack foods such as salt and vinegar crisps, and pickled foods.

* Avoid sipping continually from bottles containing carbonated drinks. It's better to drink them in one go.

* Don't brush your teeth immediately after drinking a fizzy drink or a fruit juice. Wait for at least 40 minutes or an hour.

* Do not over-brush teeth, especially with abrasive, whitening toothpastes.

* Seek medical advice for gastric problems that could increase oral acidity, such as reflux.