Comment by oaktrout

I'm skimming the results, but it looks like adult teeth had less cavities when they turned the fluoride off...and that was not observed in Edmonton where they left the fluoride on the whole time.

"For all tooth surfaces among permanent teeth (Table 1a), there was a statistically significant decrease in Calgary, for the overall mean DMFS, which was not observed in Edmonton."

Based on their data, you could argue that fluoride increases cavities in adults... I'm not making that argument. I agree with you in that I think confounders are at play and the difference attributed to fluorinated water isn't as large.

People will use this study to take about the rampant tooth decay in Calgary, ignoring that there is roughly as much decay in Edmonton which had the fluoride on the whole time.