FLUORIDATION OF WATER AND DENTAL DECAY
A BRIEFING PAPER BY THE
CHIEF MEDICAL OFFICER, PROFESSOR SIR LIAM DONALDSON, AND THE CHIEF DENTAL OFFICER, PROFESSOR RAMAN BEDI
The problem
Dental decay remains an extremely common disease which is strongly related to socio-economic status. Although the disease is largely preventable, and despite substantial improvements in dental health over the last thirty years, there remain many areas of England where there are considerable numbers of children with the disease, which causes pain and infection. For example, in the north of England in the school year 2001/02, 44% of five year old children had active tooth decay and each of those children had on average three and a half decayed teeth. In the same year in London the figures were 35% and three and a third respectively. If prevention fails the only treatments are fillings and extractions. Young children in particular find dental care difficult to tolerate and for many the solution involves a general anaesthetic in a hospital setting with multiple teeth being taken out. Dental decay is also a problem for adults. In 1998, 46% of adults in England had active tooth decay and 6% had 6 or more decayed or unsound teeth. In both children and adults there are major inequalities with a far greater prevalence of decay in the poorer sections of the community.
There has been a marked reduction in the extent of dental decay in the population over the last 30 years. It was common in all parts of the population but now most of the dental decay problem is centred in areas of social deprivation. However, the reduction in tooth decay has now stopped and it seems that further improvement is unlikely without additional preventive action.
How fluoride works
Extensive research has been undertaken on the mechanisms by which fluoride prevents dental decay. The predominant effect is direct on the tooth surface (a topical effect). Through its interaction with the surface of enamel, fluoride in saliva and in dental plaque inhibits de-mineralisation, and promotes re-mineralisation on the surface of the tooth. In other words fluoride stops teeth decaying and actually encourages repair of very early decay. Thus fluoride is important throughout life for anyone with teeth, thereby benefiting both children and adults. Fluoride also works through a systemic effect by being built into the enamel during the development of the teeth and is, therefore, of extra importance during the first 12 years of life.
Why water fluoridation?
Fluoride can be delivered to individuals as a dental preventive measures through a variety of mechanisms, one of which is drinking water, in which the fluoride level is adjusted to one part per one million parts of water (1 ppm or 1 mg/litre).
Fluoride is naturally present in virtually all water although in England and Wales usually at less than the levels necessary to prevent decay. Some parts of the country, however -for example Hartlepool and parts of Essex -do have water with natural fluoride at around the optimal level to prevent decay. These areas have been important demonstrators of the beneficial effect of fluoride on dental decay.
Water fluoridation works through both mechanisms of fluoride action - systemically (being built into the tooth structure) while the teeth are being formed and then topically (in contact with the tooth surface) throughout life. An important public health benefit of this method of providing fluoride is that any person with a fluoridated central water supply will receive fluoride without needing to take any personal action. The method is cheap - typically no more than about 50p per person per year with the cost met entirely by the NHS rather than falling on individuals.
About six million people in England drink water containing fluoride at the optimal level, mainly in the north-east and western midlands. Many of those schemes have been in operation for some 40 years. Water fluoridation is widespread in the USA, where some 160 million people drink fluoridated water. Forty-three of the 50 largest cities in the USA are fluoridated. Major scientific reviews of the benefit and health impact of water fluoridation have been conducted on a number of occasions over many years, both in the U.K. and USA, and have concluded that water fluoridation is effective at preventing tooth decay and does not cause harm to general health.
In 1999 the Government asked the University of York to carry out a further consideration of the available evidence using the technique known as systematic review. The York team was critical of much previous research as being of poor quality and did not include those studies in their considerations. From the evidence they did include in their review the team concluded that fluoridation resulted in, approximately, an additional 15% of children having no evidence of tooth decay and an average of 2.2 less teeth affected by decay. It also suggested that in areas with higher levels of decay there would be a greater reduction in caries. The editors of the Cochrane Oral Health Group -a group of researchers who carry out reviews of health care measures -have recently estimated that the effect reported in the York report is that of a "preventive fraction" or percentage decay reduction in the order of 40%.
Alternatives to water fluoridation
Fluoride can be made available to individuals via other mechanisms. They all require ongoing positive personal action by the individual concerned (and in the case of younger children by a parent or other carer). Some also require action by a dental professional. In other words, to be effective, they need people to alter their behaviour and sustain that behaviour change.
The Cochrane Library has recently (2003) published several systematic reviews which help to describe the level of impact these various other measures have on decay levels. A direct comparison with the York Report is not possible because of differences in the ways in which results were reported, but the following summarises the position:
Brushing teeth with toothpaste containing fluoride between 1000 and 1S00ppm will reduce decay by approximately 24%. There are additional benefits because of the improvement to gum health from tooth brushing.
Professionally applied varnishes will reduce caries by approximately 33% in milk teeth and approximately 46% in permanent teeth. These are very strong varnishes containing 22,500ppm, which have to be applied repeatedly and by professionals. They are not suitable for use in very young children.
The use of fluoride gels will reduce decay by approximately 19%. They, too, have to be applied repeatedly and by professionals.
Fluoride-containing tablets and drops have been shown to be effective in preventing caries in clinical trials but their use as an 'at home' treatment has been disappointing due to poor compliance. There is also some good evidence that they are associated with more dental fluorosis. Given the emphasis on the need to provide fluoride on the surface of the teeth over an extended period their use cannot be recommended routinely.
School milk fluoridation has been trialled in a number of countries, including two trials reported in the UK. The evidence from those UK trials is equivocal. Salt fluoridation has been used in a few countries, most notably Switzerland, but has not been tested in the UK. In any event the advocacy of salt consumption would not be appropriate in the UK for health reasons.
Dental decay can also be largely prevented on an individual basis by dietary means. However there is no evidence that it is possible to alter people's diet to this extent on a population basis and it is therefore not currently a practical public health option.
In summary, an alternative to water fluoridation is fluoridated toothpaste -the other techniques are not practical as public health measures. But water fluoridation delivers greater reductions in decay than toothpaste and reaches the whole population rather than just those who adhere to a regular cleaning regime using fluoride toothpaste. It is also cheaper -water fluoridation costs around 50p per person per year; a year's supply of toothbrushes and toothpaste costs around £10. So there are important reasons to consider water fluoridation as the preferred method of preventing tooth decay on a population basis and improving the health and welfare of poorer communities.
Safety of water fluoridation
The UK's Water (Fluoridation) Act 1985, since incorporated into the 1991 Water Industry Act, allows hexafluorosilicic acid (H2SiF6) and disodium hexafluorosilicate (Na2SiF6) to be used to increase the fluoride content of water. The published Code of Practice on Technical Aspects of Fluoridation of Water Supplies (Department of the Environment, 1987) gives specifications for these substances and states that 'the product. ..must not contain any mineral or organic substances capable of impairing the health of those drinking water correctly treated with the product'. For H2SiF6, limits are given for a number of possible impurities, including for iron, heavy metals, sulphate, phosphate, and chloride. The specification for Na2SiF6 powder requires a minimum of 98% m/m of the pure chemical, and gives maximum limits for impurities, including heavy metals (as lead) and iron. No other substances are allowed to be used in the fluoridation process, other than an anti-caking agent (the identity of which must be disclosed) in the case of Na2SiF6. Synthetic detergents are not permitted.
Thus there is no likelihood, in normal operation, for any fluoridation plants to introduce other compounds into the drinking water supply (other than approved anti-cakinq aqents and any impurities present in the fluoridation chemicals).
The amount of fluoride present in the water is limited to 1.5 mg/1 by Directive 98/83/EC i.e. 1.5ppm. Thus in those areas of the UK where the natural level is higher than this the concentration has to be reduced usually by dilution.
Medical problems of water fluoridation
The York Report not only reviewed the evidence about the effectiveness of water fluoridation in preventing dental decay but also considered evidence about adverse effects. The York team found no evidence of an association between bone fractures, infant mortality, or cancer and water fluoridation. York also said that some other possible negative outcomes such as 10 and congenital defects required further high quality research.
Following publication of the York Report the Government asked the Medical Research Council (MRC) to advise on any further priorities for research into water fluoridation. The MRC report (2002) recommended routine monitoring of factors such as cancer as a matter of good practice. No further research was recommended for bone fractures unless research demonstrates important differences between the bio-availability of naturally occurring and added fluoride. MRC concluded that research on a number of other possible negative health outcomes was of low priority. The Chief Medical Officer and Chief Dental Officer are to report to Ministers on the implications of the MRC report for government policy on fluoridation in the autumn.
In considering the possibility of adverse health effects length of exposure may be relevant. There is over 40 years experience in England (as in Birmingham) of artificial fluoridation, but generations of experience in some communities of natural fluoride levels matching those used in water fluoridation schemes. No evidence of harm has been demonstrated in areas of England with natural fluoride at around 1 ppm but it is important to be sure that such results are transferable to areas with artificial water fluoridation. The MRC recommended that natural and artificial fluoridation were investigated further by looking to see if there were any differences in bio-availability of fluoride in the two situation. This work has been commissioned by the Department of Health and the results are awaited. If the bio-availability is shown to be the same then it will be possible to look to long term studies of water fluoridation over generations (rather than our 40 year experience) in naturally fluoridated areas and use the results on general health found there to predict outcomes in artificially fluoridated areas. If the bio- availability is the same there is no reason to suppose that health outcomes would be different in naturally fluoridated areas and in ones where the level has been topped-up to reduce dental decay.
Dental fluorosis
Dental fluorosis is characterized by an alteration of dental enamel which affects some of the teeth and may be minor or severe. It results in white or in its severe form brownish spots on teeth resulting from poor mineralization and porosity of the enamel. The problems it causes are generally more aesthetic than pathological and, in the less severe forms, are even considered to be more aesthetically pleasing. The first signs are light white horizontal and parallel lines, extending progressively to opaque whitish spots, gradually increasing in size. In severe forms, yellow or brownish spots are present with, at the ultimate stage, eroded areas of enamel. With water at levels up to 1 ppm the severe forms of fluorosis are extremely rare and associated with other uses of fluoride. From an aesthetic point of view, the critical phase for the development of fluorosis is from 20 months to five years during the development of the most visible teeth, the incisors and canines. Dental fluorosis can occur in both fluoridated and non- fluoridated areas and can be attributed to fluoride supplementation and early tooth brushing behaviours as well as to water fluoridation
Dental fluorosis was identified by the York Report as the one adverse effect for which there was evidence. They reported a dose response effect -the more fluoride in the water the more people have fluorosis and the more severe it is. The analyses of world-wide research from the York report showed that around 15% more people in fluoridated areas had fluorosis and that 4% more might have fluorosis of aesthetic concern. In the UK, the current prevalence of dental fluorosis is probably lower than that reported by York from their studies of world- wide research and the consensus expert view is that other forms of fluoride taken on an individual basis such as ingested toothpaste and fluoride drops and tablets are important risk factors. In the UK experts believe that the swallowing of adult- strength fluoride toothpaste by very young children contributes significantly to the problem of dental fluorosis. For a number of years dentists in the UK have advised parents of young children at low risk of dental decay to use a small pea- sized amount of lower fluoride toothpaste under parental supervision. There is evidence that parents are following this advice. In a recent study, the prevalence of aesthetically important dental fluorosis in fluoridated Newcastle was 3% and in non-fluoridated Northumberland was 0.5%, considerably less than the historical data from many countries which were considered by the York team. What is of major importance is to ensure that in an area where water fluoridation is introduced extensive publicity is undertaken to ensure that other forms of systemic fluoride use (tablets and drops) are stopped.
Conclusion
Fluorides prevent tooth decay, which remains a significant public health problem in parts of England. From a public health perspective, water fluoridation is the delivery method of choice to bring about population improvements in dental health, and should be considered locally when it is desired to reduce inequalities in levels of dental decay.
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Sir George Young Bt MP: Constituency and Parliamentary Website 