WM Thomson - Professor of Dental Epidemiology and Public Health School of Dentistry

There is a compelling public health case for community water fluoridation. Children and adults have better teeth because of it, and the oral disease burden from not having community water fluoridation is more extensive than many people realise.

A number of recent correspondents have questioned whether community water fluoridation is no longer effective. Recent New Zealand research highlights the continuing benefits of community water fluoridation, with studies in Southland and Wellington/Canterbury confirming its ongoing benefits. The Southland study showed that 10-year-old children who had never lived in a fluoridated area had (on average) twice the tooth decay experience of those who had lived all of their lives in fluoridated areas. In the Wellington/Canterbury study-even without looking solely at lifelong residents-children in fluoridated areas were about half as likely to have tooth decay than those in the nonfluoridated areas. Both the Southland and Wellington/Canterbury studies clearly demonstrated that social inequalities in oral health were considerably more severe among children in areas without community water fluoridation. That is, the difference between poor children and those from well-off households is much greater in areas without water fluoridation. These findings are supported by national data on 5-year-olds and 12-year-olds which show clearly that ethnic inequalities in oral health are much greater among children in areas without community water fluoridation.

Every year, about 5,000 New Zealand children need to receive dental treatment under general anaesthetic because they have too much decay to be able to be treated conventionally. In 2002, a report was published from an evaluation of the numbers of Otago children who have had to be treated for tooth decay in hospital under general anaesthetic. It showed that almost 40% more came from nonfluoridated areas than we would expect to see if fluoridation really did have no effect on the community's oral health. This is a compelling finding, and demonstrates clearly that there are greater numbers of children with very severe disease in areas without community water fluoridation.

Recent New Zealand work on oral-health-related quality of life has documented the considerable burden on those children and their families. It is clear that we are not just talking about "holes in teeth": a young child with toothache is unable to eat or sleep well, and the disruption extends to the entire household. Where older children are concerned, a recent Taranaki study showed that, not only were the 25% of children with the most severe tooth decay experiencing more day-to-day pain, but they were less able to chew their food, more worried about their oral condition, teased more by other children, and were more likely to avoid smiling and laughing because of embarrassment about their teeth.

The benefits of community water fluoridation are not just confined to children, however. This year, an important international systematic review of studies on adults found that tooth decay experience was lower by 27% among adults living in fluoridated communities. This is an important difference. In line with the rest of the Western world, New Zealand's population is "greying"; people are living longer, and women are having fewer babies (and later). Along with this increase in the numbers of older people, more and more of them are keeping their own teeth (or some teeth at least!). In 1976, for example, 72% of those aged 65 to 74 years had no natural teeth; by 1988, this had fallen to 59% and it is projected to be about 30% by 2011 (and 14% by 2031). Recent dental studies where older people have been followed over time show that their tooth decay rate is at least as high as that of adolescents, and considerably higher if ongoing tooth loss is taken into account. Furthermore, it has been shown to be twice as high again for people living in rest homes, and twice as high again among those who have dementia. In general, very little in the way of organised dental preventive care goes on in rest homes, and therefore any advantage that can be conferred through water fluoridation is to be welcomed.

It's not just older people, either: data from the University of Otago's Dunedin Multidisciplinary Health and Development Study suggest strongly that tooth decay continues at a constant rate through adult life. Moreover, the Study members who have spent all or most of their lives in fluoridated areas had lost far fewer teeth by the time they were in their early 30s. The simple public health measure of adjusting the background fluoride level (about 0.3 parts per million, or ppm) to about 0.7 ppm will help to reduce tooth decay among adults of all ages (surely a particularly important consideration in a country with very little in the way of a "safety net" for adults who cannot afford dental care). The ongoing benefits of community water fluoridation are as likely to be enjoyed by young adults and old people as they are by children.

The safety of community water fluoridation has been subject to regular reassessment, not least in New Zealand, where the most recent review (conducted in 2000) found no cause for alarm, but recommended continued monitoring of the evidence.

Fluoride in the water acts directly on the teeth to help reverse the very early "etchings" of the tooth enamel which are the way in which tooth decay begins. The most efficient and effective way to deliver these benefits is frequently and at low concentrations. Having fluoride in the drinking water is the most efficient way to do this.

The scientific evidence shows that there remains a very strong public health case for the continued use of community water fluoridation to improve New Zealanders' oral health and quality of life.

WM Thomson BSC BDS MComDent (Otago) MA (Leeds) PhD (Adel) FICD

Professor of Dental Epidemiology and Public Health School of Dentistry

The University of Otago