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Does Fluoridation Reduce Tooth Decay?



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When fluoridation began in the 1940's and 50's, researchers reported dramatic declines in tooth decay, often 80% or more when comparing fluoridated and non-fluoridated communities. As a result, fluoridation quickly became a  widespread public health policy. Unfortunately, modern studies, using better study design and more robust statistical methods, have not replicated the dramatic early results, although many studies still show some benefit.

The largest study (in terms of study participants) ever conducted in the United States was recently published (Fall 2007) in the Journal of Public Health Dentistry (Vol. 67, No. 4, Maupome et al.). Although the study did find a small benefit of about a 5% reduction in dental costs for some study participants who received fluoridated drinking water, the majority of study participants actually did better without drinking fluoridated water.

The second largest study ever conducted in the United States ( full paper available here ) looked at the number of decayed, missing, and filled tooth surfaces (DMFS), to see if there was a difference between fluoridated and unfluoridated communities. The study reported a 25% lower DMFS score in the fluoridated communities. In terms of cavities, this DMFS score translated to 0.6 less cavities per child, or about one half of one cavity per child. Clearly this was not a huge benefit, but any reduction in tooth decay is a good thing. Unfortunately, there was a major problem with the study report - the authors did not report any statistical analysis. This is normally reported because it is important to evaluate whether the study data demonstrates a result that is not likely to be due to random chance. Independent scientists who were skeptical of the results from this study decided to carry out a statistical analysis of the data on their own, and they discovered that the results in fact were not statistically significant ( full paper available here ). Furthermore, they noticed that the findings from the partially fluoridated communities were omitted from the original study report. As it turned out, the partially fluoridated communities had an even lower DMFS score than the completely fluoridated communties. This presents a problem for the fluoridation hypothesis, because you would expect the partially fluoridated communities to have tooth decay rates that were somewhere between the fluoridated and unfluoridated communities, if fluoridation was in fact reducing tooth decay.

Additional inconsistencies in the fluordiation hypothesis have been found in fluoridation cessation studies. At least five major studies published since 2000 have not found an increase in tooth decay when fluoridation has been discontinued. Especially notable was a study conducted in Cuba with a high proportion of disadvantaged children. This study was especially significant because fluoridation is often cited as a mechanism to reduce ineqaulities in dental health care among disadvantaged children. ( Cuba study , Canada study , Finland study , Germany study , United States study )

Nonetheless, single studies, even those involving large populations, can only offer a limited picture of the effectiveness of fluoridation. Therefore scientists periodically attempt to pool the results of many studies together, to see if a consistent pattern emerges. This type of study is often referred to as a "meta-analysis." The largest such study to date was the so called "York Review," commissioned by the public health service of the British government. The full study exceeds 100 pages in length, but a concise letter on the Review's findings was written by the Chair of the Review's advisory group, Dr. Trevor Sheldon ( text of the letter ). A more recent meta-analysis was published in the journal Clinical Oral Investigations ( study abstract ) by Pizzo et al. Both the York review and the Pizzo review found that fluoridation does not always demonstrate a reduction in tooth decay, and that even in communities where it does appear to be effective, the reduction may not be clinically significant (less than one cavity per child).

Looking at fluoridation on an even larger scale, by comparing whole countries, the practice does not appear to provide a signifcant benefit. A comparison of tooth decay trends in fluoridated and unfluoridated countries (using data from the World Health Organization) was recently published in the journal Fluoride ( Read the full paper ), and an adaptation of the study was published in the October 6, 2007 issue of the British Medical Journal.

 






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