The main argument put forward by New Zealand promoters of water fluoridation is that it might reduce tooth decay in children who do not brush their teeth.
The assumption is that these are kids from poor families, who are overly represented by Maori and Pacific Island ethnicities, and that oral hygiene measures such as tooth brushing are not complied with either because families cannot afford toothbrushes and toothpaste, they are lacking in health education, or the parents are too busy to spend time teaching their kids to clean their teeth.
While water fluoridation is seen by some as mass medication, undermining the individual's freedom to choose or refuse treatment, the public health authorities consider this is overriden by the requirement to act as a "safety net" whereby children (there is no reliable evidence of any benefit to adults) who do not clean their teeth can obtain some protection from tooth decay.
There are a number of problems with such arguments, as follows:
1. It is widely acknowledged that the action of fluoride on delaying tooth decay is topical, not developmental. Swallowing fluoridated water has next to zero effect on making tooth enamel more resistant to plaque acids. Furthermore, the increase in baseline salivary fluoride concentrations in the mouth in children living in fluoridated water areas is generally inadequate to have any cariostatic benefit. see mechanism.
2. if the children are not brushing and the plaque is allowed to grow on the tooth surface, it will act as a barrier to fluoride penetration towards the enamel surface, so ingesting fluoride at 0.7-1ppm is a poor substitute for cleaning.
3. Any minimal benefit which could occur by a small increase in the uptake of low level fluoride would be completely overpowered by factors which encourage tooth decay, such as sugar in drinks and food. Therefore ingesting low levels of fluoride is a poor substitute for diet education g for children and caregivers.
4. We do not know how much water such "target" groups actually drink. They may not drink water at all, so they will not gain any effect from such a method of delivery.
5. The recommended amount of toothpaste for children to apply twice daily is the size of a grain of rice until age 3, and the size of a small pea until age 12. A 100gm tube of toothpaste should therefore last 3 to 6 months. The cost of two packs of cigarettes would supply a child with toothpaste to last for their entire childhood.
6. Systematic Reviews of research have repeatedly not found any reliable evidence of water fluoridation addressing social inequalities. see York Review and SCHER review
7. New Zealand school dental data do not suggest any "gap closing" between Maori and PI, and "Other" groups from water fluoridation.
8. Increased decay rates in Maori compared to European may also relate to other factors such as less access to care, urban/rural distribution, SES, Education Levels, and earlier emergence of teeth in Maori, which means comparing decay at a particular age Maori teeth have been present up to 18 months longer, therefore more opportunity to decay. Such factors are more plausible than lack of fluoride, and fluoridating the water supply will not effect these factors either. Which could explain why we see no difference in the data.
But could it cause harm?
Assessments of total fluoride intake suggest that Maori and Pacific islanders, as well as low socio-economic groups are not only more likely to have a poorer diet, with less Calcium (which helps to reduce the bioavailability of free fluoride ions) but are much more likely to have a higher daily intake of fluoride, so having fluoridated water increases the risk of chronic overdose
This has been linked to increased risk of neurological (brain)disorders, hypothyroidism, asthma and diabetes, all diseases where Maori and PI groups are overrepresented.
There is therefore a real possibility that water fluoridation could be increasing the social inequalities in general health.
Are there alternatives?
Tooth decay is caused by too much sugar and lack of oral hygiene. Preventive programs in many countries which target the at risk groups for tooth brushing and education programs have been shown to be most effective at reducing tooth decay in children, and in developing good habits which, like the "teach a man to fish" parable, last a lifetime.