'Tooth scouring fits our deep-seated notion that cleanliness is equivalent to moral worth. But the belief in ritualised brushing has also been powerfully reinforced by commerce, for reasons that have more to do with profit than health promotion,' Mr Cook argues.
The brush and paste manufacturers are ever keen to sell more of their goods - the three-headed 'superbrush' being only the latest example - while the confectioners are only too eager to divert attention from the role of sugary foods. Their interests come together in unholy alliance to persuade us that better brushing is the key to preventing decay, he says.
'Saying teeth should be cleaned regularly is advice that is easy for dentists to give and easy for their patients to follow. But, as a means of preventing tooth decay, it is simply not the answer,' Mr Cook says.
Sugar on its own does not dissolve teeth. It is the acids produced by bacteria, notably a strain called Streptococcus mutans, that erode the enamel. But it is only when provided with a ready supply of sugar, their favoured food source, that the bacteria cause significant harm, bathing teeth in the acidic waste products of their metabolism.
The evidence that sugar leads directly to the production of enamel- dissolving acid could not be more clear. Sensors can now record acidity in the mouth as various foods are eaten. During a sugary snack, acidity quickly rises, and it remains high for up to an hour. Sweets between meals and sugary puddings all ensure that enamel is under acid attack for much of the waking day.
The dental plaque we hear so much about is formed by clumps of bacteria stuck to the teeth. The argument goes: if we could remove the bacterial plaque by brushing, surely there would be no decay, however much sugar we consumed.
This idea is attractive to those concerned with dental hygiene, but ineffective in practice. It is true that if we could eliminate all bacteria, there would be no dental caries. Experiments in which animals' mouths are kept chemically sterile show this. Unfortunately, brushing alone cannot eradicate plaque, which remains between the teeth and in natural fissures that give them the rough surface needed to grind food. However elegantly designed are the bristles and brush heads that we use, many areas of tooth surface simply cannot be reached. And it is here that the insidious process of decay begins.
'Oral hygiene does bring many benefits,' says Mike Grace, editor of the British Dental Journal. 'People should not think there is no need to clean their teeth, since brushing is important in preserving the health of the gums and in preventing mouth odour.'
Nevertheless, he agrees with Richard Cook that there is uncertainty in the public mind about what brushing actually does. 'Ask people what causes tooth decay and they say, 'too many sweets'. But ask them how to prevent decay and they reply, 'clean your teeth', not 'eat less sugar',' Mr Grace says.
In his Fenland village practice, Mr Cook routinely faces the confusion. Children visit the surgery with bad decay, caused by frequent sweets or sugary drinks. He explains that teeth are rotted by the acid from mouth bacteria force-fed on sugar. He advises progressive dilution of syrup until it can be left out of children's drinks altogether, and recommends sugar-free sweets.
But when he meets families in the street, the children are still sucking their familiar 'blackcurrant' drinks. 'This is the dentist,' parents remind their kids. 'You know what he'll say. You've got to clean your teeth after every meal.'
Given the common belief that brushing is the beginning and end of dental wisdom, it would make sense for dentists to be far more explicit about the role of diet in decay. Richard Elderton, professor of preventive and restorative dentistry at Bristol University, agrees. 'If you came to me with a 10-year-old beginning to experience caries, improved oral hygiene would not be my first recommendation,' he says. 'I would advise a reduction in dietary sugar and effective use of fluoride.'
While it undoubtedly helps to counter gum disease, the evidence is that oral hygiene makes relatively little difference to tooth decay, Professor Elderton believes. There have been studies in which children in one school are given intensive training in oral hygiene, while children in a comparable school are not. Years later, there is no discernible difference in decay rates. The same is true if countries with different preventive dental health strategies are compared.
'In the United States and Scandinavia, there has been great emphasis on tooth cleaning, with 'brush ins' and 'floss ins'. But the decline in caries rates in these countries has been no greater than in Britain, where we have never really had structured preventive programmes on a wide scale,' he says.
According to results released last month from the Child Dental Health Survey, 55 per cent of British children have had caries in their permanent teeth by the time they reach their teens. 'Dental decay is still a formidable problem,' said the British Dental Association. Nevertheless, over the past 20 years there has been a reduction of more than 50 per cent in the number of rotten teeth in children's mouths.
Comparison of areas with and without fluoridation suggests that this measure has had a profound effect on overall dental health. Last year, a study of pregnant women in North Wales showed that those who had lived on Anglesey, where the water supply is fluoridated, had 30 per cent less tooth decay than women from mainland Gwynedd, where fluoride is not added. Exposure to fluoride during child development is known to strengthen the crystal structure of enamel. The Welsh research suggests its use has benefits that extend into adulthood.
Professor Elderton is convinced that fluoride directly applied to the teeth in paste, rather than being incorporated into them during development, is also helpful in reducing caries. Fluoride counters the destructive effect of acidity, slowing the leaching of calcium and phosphates from the enamel. There is also evidence that fluoride can actually encourage these substances to return from saliva into the tooth.
'I advise people to brush really well once a day, before bed. The bacteria they manage to clean off will not grow to form plaque again for 24 hours,' Professor Elderton says. 'I also suggest they apply fluoride paste at a couple of other times during the day. This can be done using a finger or a toothbrush. But even if a brush is used, this should not be confused with cleaning. It is simply a way of getting more fluoride on to the teeth.'
Mr Cook accepts the value of brushing, both in preventing gum disease and in protecting the teeth with fluoride. 'A pea-sized lump of fluoride paste applied before bed, especially if the mouth is not rinsed, can encourage restoration of the enamel,' he says. But that once-nightly brushing is probably all that is needed.
For those who continue to believe in the magic of the brush, his advice is to use it in advance of eating sugary foods. It is best to remove what bacteria you can before eating a meal, not after. But for Mr Cook the most important message is that too much concern with brushing merely fudges the issue, distracting attention from the destructive role of sugar itself.
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