Page "Water fluoridation controversy" Paragraph 11

The available evidence shows that water fluoridation is effective in reducing cavities ( see effectiveness section of the main article ).

The most comprehensive systematic review found that fluoridation was statistically associated with a decreased proportion of children with cavities ( the median of mean decreases was 14. 6 %, the range − 5 to 64 %), and with a decrease in decayed, missing, and filled primary teeth ( the median of mean decreases was 2. 25 teeth, the range 0. 5 to 4. 4 teeth ), which is roughly equivalent to preventing 40 % of cavities.

The review found that the evidence was of moderate quality: many studies did not attempt to reduce observer bias, control for confounding factors, report variance measures, or use appropriate analysis.

The effect is largely due to the topical effect of fluoride ions in the mouth rather than the systemic effect of ingestion.