Why Brushing with Fluoride Toothpaste Isn’t Enough: A New Study Offers Insights
State and local policymakers are often told that community water fluoridation is no longer necessary because fluoride toothpaste alone is enough to protect teeth from decay. “If more adults and children brushed with fluoride toothpaste, we wouldn’t need fluoridation.” Such statements are common in discussions or debates about water fluoridation.
City councils in Calgary and Windsor — two large Canadian cities — were led to believe this when they voted to end fluoridation in the early 2010s. Subsequently tooth decay rose measurably in both cities. A seven-year study in Calgary found a significant increase in childhood decay. In Windsor the rate of urgent dental treatment needed by children rose by an alarming 51% in the years after the city discontinued fluoridation.
In the absence of fluoridated tap water, toothpaste use by itself wasn’t enough to prevent a spike in tooth decay. After learning of residents’ oral health problems, decision-makers recognized the error of their policy decision and voted to reinstate fluoridation, Calgary in 2018 and Windsor in 2025.
Why wasn’t brushing with fluoride toothpaste enough? A new study of adults on the Island of Ireland provides an answer to this question. The study compared “the decay experience” (cavities) of people living in different regions of the Republic of Ireland (ROI) and Northern Ireland (NI). In the ROI, fluoridation of community systems is mandatory and reaches over 70% of the population. NI does not have programs to fluoridate drinking water.
The study found that adults in the fluoridated region of the ROI had lower rates of tooth decay than those living in unfluoridated areas of NI. Decay overall was lower in adults in the ROI. The largest difference in cavities, however, was found in the narrow gaps between the teeth known as “approximal surfaces”. Decay on these surfaces, which are particularly vulnerable to plaque buildup followed by decay, was nearly 19% lower in adults living with fluoridated water, leading the authors to conclude, “These findings support an association between long-term CWF exposure and reduced dental caries experience in adulthood.”
There is no reason to believe that there is any difference between the frequency or thoroughness of brushing and flossing among the residents of the ROI and NI. This new study, however, suggests that water fluoridation may well add a layer of protection that makes approximal surfaces less prone to adult tooth decay.
