Chewing over the facts of the fluoride controversy; Dr Peter Clemenson is course leader, MSc Analytical Science, School of Applied Sciences, University of Huddersfield and recently advised a scrutiny committee set up by Kirklees Council on fluoridation of public water.

Byline: Dr Peter Clemenson

HEALTH Secretary Alan Johnson wants fluoride to be added to England's public drinking water supplies in the hope of reducing tooth decay throughout the country.

The addition of fluoride to potable water is still a controversial issue, despite the fact that in several countries, including America, a majority of the population enjoys the benefits of having fluoride added to their water.

For well over 50 years, it has been known that adding fluoride to public water in very low concentration inhibits tooth decay or dental caries.

However, the presence of fluoride has been linked to a condition known as mild dental fluorosis which is observed as white patches on the teeth. Fluoride is added to drinking water by the water companies in a form of fluorosilicate compounds which breakdown to produce soluble fluoride at a concentration of around one part per million (ppm).

This is one milligramme per litre of water, a similar amount to sharing one sugar cube amongst a thousand cups of tea. The lifetime of the fluoride ions in the body is just a few hours, so we continually need to ingest low levels of fluoride in our drinking water if the benefits are to be effective.

Fluoride in trace amounts is present in most foodstuffs. It is also present in wine, beer and in some teas; in these cases, levels being quite high, depending on the sources of these drinks. About 90% of all toothpaste sold in the UK contains fluoride, usually in the form of sodium fluoride (about 0.24% or 1100 ppm fluoride).

So how do fluoride ions help protect people from dental decay or caries? The hard surface of human teeth that the enamel is made of is calcium hydroxyphosphate (hydroxyapatite).

It is the basic hydroxide group in calcium hydroxyphosphate that makes the enamel prone to attack from acids in plaque, food and saliva. However, the hydroxide group can be replaced by fluoride to form a calcium fluorophosphate (fluoroapatite) and it is this which makes the teeth less prone to acid attack and more resistant to dental caries.

Fluoride, when concentrated in plaque and saliva, inhibits the demineralisation of enamel and helps the remineralisation or recovery of enamel which has been damaged or undergone acid attack.

The sizes of the fluoride and hydroxide units are similar, which makes them easily exchangeable.

This exchange process is most apparent in the very young or the very old.

As children grow, their first teeth are very prone to dental caries, and in older people, when the gums shrink with age, part of the root of their teeth becomes exposed making them prone to root caries.

However, because of a child's susceptibility to dental fluorosis it is generally recommended that parents brush the teeth of their children with fluoride-free toothpaste until they learn to spit it out.

In some parts of the country, such as Durham and Hartlepool, drinking water is naturally fluoridated by water being percolated through fluorinated minerals such as calcium fluorite before getting to their reservoirs.

In other areas, such as Birmingham and Newcastle, fluoridation of water supplies has been taking place for over 40 years.

West Midland NHS has a very informative website, which compares the dental statistics for areas in which they have fluorinated water and areas that don't.

The World Health Organisation recommends that potable water should contain 1.5 ppm of fluoride.

Yorkshire Water currently provides water to the people in Huddersfield without any added fluoride.

The natural concentration of fluoride is 0.1 ppm, which is actually lower than in some commercially available mineral waters.

TAP INTO WATER CAMPAIGN: The debate continues about whether fluoride is something that should be added to our drinking water [e-mail]

Fluoride in trace amounts is present in most foodstuffs. It is also present in wine, beer and in some teas

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TAP INTO WATER CAMPAIGN: The debate continues about whether fluoride is something that should be added to our drinking water