Caries prevention on tap

With nearly 50 years of fluoridation in Ireland and 65 in the US, Dr Joe Mullen PDS provides an update on the latest thinking on the public health policy

The first water fluoridation schemes began in Ireland in 1964, following the Health (Fluoridation of Water Supplies) Act 1960. Currently, something in the region of 70 per cent of the entire population of Ireland is served by fluoridated water.

Water fluoridation is practiced in a numberĀ of countries, including the United States, Australia, New Zealand, Canada, Israel, Singapore, Malaysia and the United Kingdom. Fluoridated salt and fluoride supplementation are common in most other developed countries. As a rough estimate, approximately 400 million people across the globe consume fluoridated water daily.

The purpose of water fluoridation is to prevent dental decay. There have been many studies worldwide which have measured the impact of water fluoridation on caries and, unsurprisingly, the benefit of this one policy is shown to vary according to the risk of caries in the society. If the risk of caries is low, water fluoridation will tend to bring little additional benefit; if the risk is high, the opposite is true.

Ireland is home to a high caries risk society. Lifestyle surveys have shown that we experience a highly cariogenic diet, and the public preventative dental services are relatively poorly resourced, particularly in comparison with the northern European countries.

Surveys carried out in Ireland, and particularly across the border with Northern Ireland – which has a similar caries risk profile but does not have public water fluoridation schemes – demonstrate a significant benefit from water fluoridation in reducing dental decay levels. Research on adult dental health has also shown that this benefit extends into late adult life.

It is only in recent years that it has been possible to look at long-term benefits to adult dental health, as insufficient time had elapsed to gauge the benefits. However, we now have a population in the United States which has had 65 years, and in Ireland 47 years, exposure to water fluoridation. The fact that earlier studies were carried out almost exclusively on childrens’ dental health has led to the erroneous assumption that water fluoridation is only concerned with protecting children’s teeth; it is in fact directed at better health for everyone’s teeth.

Key landmarks of 2000s

In the past decade there were a number of key international reviews of the safety and effectiveness of water fluoridation. Among these were the Systematic Review carried out by NHS Centres for Review and Dissemination 2002 (the York Review) and the Medical Research Council 2005 (both United Kingdom), the National Health and Medical Research Council Review 2007 (Australia), and the Forum on Fluoridation Report 2002 (Ireland). All of these reviews concluded that water fluoridation was beneficial and that, to date, there was no evidence of any harmful general health effect.

Opponents of fluoridation are often motivated by a concern that water fluoridation is in some way unethical. The argument is that fluoridation is a forced medication and that this perceived offence to personal liberty outweighs any benefits that may arise. The Forum on Fluoridation report contains a chapter on the ethical issues facing water fluoridation. Its conclusion is that fluoridation is ethical, assuming it is beneficial. It states: “Even given a modicum of risk, we might still ask whether it could ever be ethical to withhold an on balance beneficial treatment, to fail to prevent suffering when it is within our power? To do so would be to deliberately fail to protect and promote the health of people in our community.” The Forum report is available at http://www.dohc.ie/publications/pdf/fluoridation_forum.pdf

In the United Kingdom, the Nuffield Foundation produced a report on the ethics of a number of public health issues, including water fluoridation. This is a comprehensive and detailed discussion of all ethical issues around water fluoridation, but it has the following to say on the ‘forced medication’ argument: “The principles of consent, minimising interventions that affect important areas of personal life, and not coercing adults to lead healthy lives could in principle be used to argue against water fluoridation.

“We reject the view that, on the basis of arguments about interference in personal life and coercing ordinary adults, the fluoridation of water should be prohibited outright. Instead, the acceptability of any policy involving the water supply should be considered in relation to the balance of risks and benefits, the potential of alternatives, and, where there are harms, to the role of consent.”

The Nuffield report on public health issues can be accessed at http://www.nuffieldbioethics.org/sites/default/files/Public%20health%20-%20ethical%20issues.pdf

The 2000s saw the publication of a large number of studies worldwide which reported the benefits of water fluoridation in reducing dental decay rates. In Ireland, national dental health surveys were conducted between 2000 and 2002 on the dental health of adults and children.

The adult survey showed a benefit to dental health of adults living in fluoridated areas, with more teeth retained. The percentage of adults with 18 or more sound untreated natural teeth in the 35-44 age range was 47 per cent in the fully fluoridated population as compared to 25 per cent in the non-fluoridated group.

The children’s survey was unique in that it was an all-island study and so contained a completely non-fluoridated population, the residents of Northern Ireland. The so-called ‘non-fluoridated’ population of the Republic are, in fact, somewhat partially fluoridated through the ‘Halo Effect’. This effect occurs when a child nominally living in a non-fluoridated area will, in fact, receive some of the benefits of fluoridated water from travelling to fluoridated areas (for example when going to school in a fluoridated town) or through consuming food and drink prepared with fluoridated water (such as bread baked in a fluoridated town).

It was long suspected that a comparison between children’s groups within the Republic of Ireland might provide an underestimate of the impact of water fluoridation due to this Halo Effect. Thus for this survey, the decay experience was measured for three populations; the fluoridated and non-fluoridated populations of the Republic of Ireland, and the population of Northern Ireland. The survey results showed the fluoridated population in the Republic as having the order of 43 per cent, 31 per cent and 39 per cent fewer cavities than the Northern Ireland children at 5, 12 and 15-years-of-age respectively while the ‘non-fluoridated’ population in the Republic also had marginally fewer cavities than the Northern Irish children, something of the order of 4 per cent, 15 per cent and 11 per cent for 5, 12, and 15-year-olds respectively.

Another cross-border study was published in 2006, sponsored by CAWT (Co-operation And Working Together), a collaborative body comprising the regional health authorities on both sides of the border. The CAWT study not only measured dental caries and enamel fluorosis rates, this time for 16 year olds, but also measured Oral Health Related Quality of Life (OHRQoL). Again, caries levels were significantly lower among fluoridated children, while dental fluorosis levels were higher. The OHRQoL data suggests that the impact on self esteem from the typical fluorosis presentation is not negative.

The report states that: “Fluorosis was not associated with increased negative oral health impacts. This is supported by research elsewhere (Michel-Crosato et al 2005, Robinson et al 2005). In fact, fluorosis was associated with improved oral health- related quality of life, as in fluoridated areas there was less experience of obvious decay, filled teeth, filled surfaces and filled smooth tooth surfaces.” Another finding from the study was that fluoridation may help reduce socio-economic inequalities. The full study can be accessed at http://www.cawt.com/Site/11/Documents/Publications/PCCC/CrossBorderFluorideStudy.pdf

Public policy developments of recent years began with the setting up of the Forum on Fluoridation by the minister for health in 2000. The forum reported in 2002 and made a number of recommendations which included the continuation of water fluoridation. Following on from the recommendations of the forum, the minister established the Expert Body on Fluorides and Health, which provides advice for the Department of Health on matters connected with fluoridation. It also reviews and evaluates the latest evidence concerning the use of fluorides and their effects, and on new emerging issues generally.

The legislation governing fluoridation defined the optimal concentration of fluoride in water as being within the range of 0.8 to 1.0 parts per million (ppm). In 2007, this level was redefined as being 0.6 to 0.8 ppm, in order to allow for the changes in population exposure due to the widespread use of fluoridated toothpastes and other fluoride- containing products.

The SCHER Report 2011

In 2007, the European Commission asked its Scientific Committee on Health and Environmental Risks (SCHER) to review the safety and effectiveness of water fluoridation. A panel of seven permanent members of SCHER and four invited reviewers formed the review committee. The expertise of this committee was heavily weighted towards toxicology and biochemistry.

The committee published a preliminary report and invited interested parties to critique this via written submission and at a public meeting in Brussels in September 2010. In June 2011 SCHER published its final report along with a report on the material that they excluded from their analysis and the rationale for so doing.

The SCHER report presented 13 conclusions. The two main areas of interest to the committee concerned the safety and effectiveness of water fluoridation. On the safety question, their conclusions can be summarised as stating that there is a lack of evidence for any general health ill-effect of water fluoridation, or any negative effect on the environment.

As for effectiveness, the committee acknowledges the effectiveness of water fluoridation but considers that the use of topical fluorides might be a more efficient alternative.

This last point is clearly quite contentious. Evidence in Ireland, with our high caries risk profile, shows a very substantial benefit from water fluoridation, particularly when compared to some societies where the caries risk profile is much lower. SCHER’s view does not appear to take into account the combined effectiveness of water fluoridation with topical fluorides, as it is known that the combined benefit of these approaches is greater than the exclusive use of each on its own.

Another conclusion that is quite interesting from a general health viewpoint concerns the chemistry of fluoride in water. SCHER concluded that: “Hydrolysis of hexafluorosilicates, used for drinking water fluoridation, to fluoride was rapid and the release of fluoride ion was essentially complete. Therefore, the fluoride ion is considered the only relevant substance with respect to this opinion.”

The product used to fluoridate water in Ireland is hexafluorosilicic acid (H2SiF6), but it is important to know that this is not what comes out of the taps in your house. This acid reacts with water to produce free fluoride ions and sand. There are no other by-products of this reaction. This finding also acknowledges in effect that there is no difference between naturally occurring fluoride ions and fluoride added deliberately.

Recent papers on bone health

Since the fluoride that is not excreted is retained by the body’s calcified tissues, it is logical to look at bone as a possible site of ill effects. Osteosarcoma is an obvious condition to examine, but its rarity makes epidemiological investigation difficult. As with previous reviews, SCHER did not report an association between fluoridation and osteosarcoma. Since that report was published, there have been two significant papers which give further confidence to the lack of an association.

A paper by Comber et al which compared osteosarcoma rates between Northern Ireland and the Republic of Ireland found no difference in rates1. This paper examined the data from the Northern Ireland Cancer Registry and the National Cancer Registry of Ireland on osteosarcoma incidence in the respective populations. The data was used to estimate the age-standardised and age-specific incidence rates in areas with and without drinking water fluoridation.

Only 183 osteosarcoma cases were recorded on the island of Ireland between 1994 and 2006. No significant differences were observed between fluoridated and non-fluoridated areas in either age-specific or age-standardised incidence rates of osteosarcoma. However, there is a caveat, in that the rarity of this disease means that it is much harder to be precise about any relationship; what can be said is that the existing data, collected over 13 years, does not provide evidence of a link.

A major paper by Kim et al2 using a very high-quality study design also found no relationship between fluoride exposure and osteosarcoma. This latter paper from Harvard arose from the longest and most detailed study yet into this question.

Studies which try to check on the relationship between fluoridation and a very rare condition such as osteosarcoma are particularly difficult due to the low numbers of cases involved, and the uncertainties around the amount of fluoride actually ingested.

If there is uncertainty around one of the variables being compared, it would be helpful to be as precise as possible about the other. Previous studies had tried to estimate the intake of fluoride by looking at estimates of fluoride ingestion or exposure to fluoridated water. The Kim study considered the relationship between actual bone fluoride levels and osteosarcoma. It reported that there was no significant difference in bone fluoride levels between cases and controls and that no significant association between bone fluoride levels and osteosarcoma risk was detected.

The relationship between water fluoridation and bone fracture rates was examined in a similar way by Chackra et al and reported in 20103. This study reported no association between bone fluoride levels and bone fracture rates. This finding is also consistent with the existing evidence base.

Conclusion

Water fluoridation is an important public health measure. It is listed by the Centre for Disease Control in the United States as being one of the 10 most important public health initiatives of the 20th Century.

It is an initiative which, from the very start, has been supported by the dental profession in Ireland. Indeed, in the 1960s the Irish Dental Association was at the forefront in making the case for what was then a radically new approach to the management of dental decay.

However, it is the case that the justification for the policy water fluoridation requires constant revision. If a better way of achieving the same ends becomes available, we should not hesitate to move away from this policy. Similarly, if evidence of genuine negative health effects came to light, it would require change.

We know that not fluoridating also carries health risks. We also know that if general health risks do exist, they have escaped detection in the 70 years or so that the topic has been researched. But that is not to say they do not exist.

Continued scrutiny is required.

References

1 Drinking water fluoridation and osteosarcoma incidence on the island of Ireland. Cancer Causes & Control 2011 Jun;22(6):919-24. doi: 10.1007/s10552-011-9765-0. Epub 2011 Apr 11.

2 An assessment of bone fluoride and osteosarcoma. Kim FM, Hayes C, Williams PL, Whitford GM, Joshipura KJ, Hoover RN, Douglass CW, J Dent Res 2011 Oct;90(10):1171-1176. Epub 2011 Jul 28.

3 The long term effects of water fluoridation on the human skeleton. Chachra D, Limeback H, Willet TL and Grynpas MD. J Dent Res 2010 Nov;89(11):1219-23

About the author

Dr Joe Mullen has been the principal dental surgeon for Sligo-Leitrim since 1995. He is a former member of the North Western Health Board, the Continuing Dental Education Committee of the Postgraduate Medical and Dental Board and the Dental Council of Ireland.

He is currently a member of the European Association of Dental Public Health and of the Irish Expert Body on Fluorides and Health, as well as being the current chair of the Dental Surgeons Vocational Group of IMPACT.

Dr Mullen obtained his BDS and MDPH degrees from University College Cork. He also holds degrees in public administration, information technology and healthcare management.