Is water fluoridation better than salt fluoridation?

Discussion of fluoridation here concentrates on community water fluoridation. But some countries (parts of Europe, and Latin America, for example) fluoridate their salt instead of their water.  This could be for a number of reasons – the state of the water reticulation system, or political opposition to water fluoridation, etc.

The effectiveness of community water fluoridation in reducing tooth decay is well established by research, but there has been far less research on the effectiveness of salt fluoridation. Evidence suggests the effectiveness of the two fluoridation methods is similar but new research from Latin  America found water fluoridation significantly better than salt fluoridation.

It’s a very good study, large numbers of subjects and good consideration of possible confounders. But the authors themselves suggest their findings are more relevant to developing countries than developed countries with better oral health systems.

The paper is:

Fabruccini, A., Alves, L. S., Alvarez, L., Alvarez, R., Susin, C., & Maltz, M. (2016). Comparative effectiveness of water and salt community-based fluoridation methods in preventing dental caries among schoolchildren. Community Dentistry and Oral Epidemiology.

The researchers used data from survey of the oral health of 1528 twelve-year-olds in Porto Alegro, South Brazil  (water fluoridated) and 1154 twelve-year-olds in Montevideo, Uruguay (salt fluoridated). Diagnostic procedures were standardised and the data adjusted for gender, maternal education, school type, brushing frequency, use of dentifrice, professional fluoride application, access to dental services and consumption of soft drinks.

Caries prevalence and decayed missing and filled teeth (DMFT) were measured using standard WHO procedures, and modified WHO procedures (which also included noncavitated lesions).

The graphs below show the adjusted data for caries prevalence (%) and DMFT.

Both caries prevalence and DMFT were significantly higher for children from salt-fluoridated Montevideo than similar children from water-fluoridated Porto Alegro.

Apparently this is the first study showing a statistically significant difference between water and salt fluoridated areas. Similar studies in Freiberg, Germany and Dublin, Ireland had shown no signficant differences. The larger sample sizes of the current study may have contributed to the difference. However, the authors also warn that the different situations may also be a factor.

Developing countries have higher prevalence of caries and poorer access to others sources of fluoride than developed countries. Whereas water fluoridation reaches the whole population fluoridated salt may not have such a regular use. In Uruguay the salt fluoridation programme is limited to salt for domestic use. It does not cover public and private canteens, restaurants and bakeries (which the WHO recommends).

So, an interesting study with a clear result – but one that should not be cherry picked to confirm a bias. It indicates community water fluoridation will probably be more effective than salt fluoridation in developing countries – especially if a salt fluoridation programme is not complete. But this should not be used to argue against a good salt fluoridation programme in developed countries.

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