Feature

The Whole Tooth

The fight over fluoridation is by no means over, but a new study may help to answer public concern over the practice.

By Cathryn Crane

Fluoridation is a controversial issue. The pros and cons of adding fluoride to water supplies run the gamut from the science to the ethics involved.

A new study by the Canterbury and Otago Area Health Boards aims to gather concrete data on the relationship between fluoridation and dental diseases.

The teeth of over a thousand subjects from Ashburton, Timaru, Oamaru and Dunedin will be examined in the six-month study. The researchers will use radiographs to study dental disease in 5 year olds and 14 year olds. The two groups represent baby teeth and mature mouths.

The areas were selected because they have had different fluoride strategies, says Garth Dever, principal dental officer with the Canterbury Area Health Board. These strategies range from never having had fluoridation, having had it and then stopping, and being fluoridated continuously for the last 20 years or so.

Public Indecision

This ambivalent approach to fluoridation is a consequence of the controversy over the chemical's efficacy and long-term effects. In 1953, Hastings was the first city in New Zealand to decide to take up fluoridated water supplies. This year it voted against fluoridation. Tauranga stopped adding fluoride to its water supplies in 1986 after 22 years of it, and did an about-face just recently back to fluoridation.

Promising results from Hastings encouraged many towns and cities to fluoridate their water supplies in the mid 60s and early 70s. Around 70 local and regional authorities now do so as a means of cheaply and effectively reducing dental diseases.

"I don't think there is any disagreement that fluoridation does affect dental disease patterns," says Dever. Over 90 communities around the world have been studied, and Dever notes that it doesn't matter if you're in Bratislava or Christchurch -- the data is all very similar.

Studies Queried

The significance of fluoride's effects is still debated, but there are many problems associated with the arguments. While a great number of studies have been made, methodological problems concerning sample selection make comparisons difficult. The introduction of fluoride toothpastes and the mobility of the New Zealand population has made it difficult to isolate the effects of fluoridation.

The new South Island study hopes to produce hard evidence by taking this into account and ensuring that all social and economic groups are represented.

Factors other than fluoridation have been suggested to explain the decrease of dental problems in New Zealand over the last thirty years. Such factors include possible changes in dietary patterns or a change in the bacteria inhabiting the mouth.

A 1985 study indicates that dietary patterns are unlikely to be significant. New Zealanders eat as much sugar now as they did in the early 1900s. Changes in bacteria population are more difficult to assess, as there is no long-term data on this subject.

These factors are often put forward to explain why tooth decay has declined in both fluoridated and non-fluoridated areas. However, exposure to fluoride is common even in areas where fluoridation of water supplies is not practiced. The widespread use of fluoride toothpastes and the School Dental Service's fluoride programme makes it difficult for individuals to be totally fluoride free.

Some Fluoride Essential

Fluoride is an essential constituent of the basic mineral structure that makes up bones and teeth. The body protects itself against build-up of fluoride by passing much of it in urine. The precise metabolic role and function of fluoride remains unclear, but studies have shown that the skeletal structure does not develop normally in a fluoride-free environment.

Dever admits that there has been a major change in emphasis concerning fluoride usage. Once it was thought that the substance worked systemically from within the body. People were encouraged to swallow fluoride tablets so that their bones and teeth would have a ready fluoride source.

This view has changed to the belief that a topical (surface) application is more appropriate. Dentists and dental nurses apply fluoride when cleaning teeth. Fluoride toothpastes provide a similar effect, although swallowing these toothpastes is no longer recommended. Concern over children being exposed to unnecessarily high levels of fluoride has prompted the development of fluoride toothpastes with lower levels of the substance.

As with most things, excess quantities of fluoride can prove harmful or fatal. High levels of fluoride are associated with dental fluorosis or mottling of the teeth. Excessive quantities can cause skeletal problems.

Much of the arguments against fluoridation rest on how much fluoride is too much and whether the potential dangers of over-consumption outweigh the demonstrated benefits.

How Much?

Virtually all the studies made so far point to a water content of one part fluoride per million (1 ppm) as being best. At this level the fluoride results in maximum reduction of tooth decay and minimum amounts of mottling. Raise to this around 4 ppm and mottling becomes pronounced without extra reduction in dental disease. By 10 ppm, skeletal fluorosis starts to become a noticeable problem.

There have been highly publicised suggestions that fluoride is associated with cancer and genetic damage, but scientific studies have shown little basis for this. Even in those areas where high levels of fluoride occur naturally, there is little evidence to indicate any form of carcinogenic or genetically damaging effects.

New Zealand waters naturally have a fluoride content averaging 0.4 ppm, and many authorities boost this to the recommended level with the addition of extra fluoride. In tropical countries, where people tend to drink more water, the levels of fluoridation are lower. Many foods such as fish and tea have high levels of fluoride -- some teas have as much as 2 ppm.

Table salt in New Zealand has iodine added to prevent goitre. Chlorine is commonly used to clean public water supplies. These additives have not aroused the emotiveness of the fluoride issue.

Science supports fluoridation, but ultimately the decision to fluoridate or not fluoridate rests with the populace. The onus is on the local authorities to ensure that the populace has the data to make an informed decision.

Cathryn Crane is a freelance journalist with an interest in environmental issues.