Study analyzes short-term results of defluoridating water

Canadian researchers have new evidence that links cessation of water fluoridation to an increase in caries. A recent study found schoolchildren in Calgary, Alberta, had a higher prevalence of caries in their primary teeth after the city's water supply was defluoridated.

The researchers studied the prevalence of caries in Calgary children before and after the city ended community water fluoridation in 2011. They also compared the caries prevalence of children in Calgary with those in Edmonton, where the water has been fluoridated for decades.

"Trends observed for primary teeth were consistent with an adverse effect of fluoridation cessation on children's tooth decay, 2.5–3 years postcessation," wrote the study authors, led by Lindsay McLaren, PhD, an associate professor in the department of community health sciences at the University of Calgary (Community Dentistry and Oral Epidemiology, February 17, 2016). "Trends for permanent teeth hinted at early indication of an adverse effect."

Getting the research right

While community water fluoridation is generally thought of as a good way to prevent caries, existing studies often have methodological limitations, such as lack of a comparison community. Most community water fluoridation research also often focuses on community water initiation, as opposed to cessation, and most studies occurred prior to 1975.

More than 30 communities in Canada have stopped fluoridating water since 2005, according to the study authors. When Calgary ended community water fluoridation, the authors wanted to take advantage of the opportunity to provide recent evidence about community water fluoridation's effect on caries.

"The purpose of this study was to examine the impact of fluoridation cessation on children's dental caries," McLaren wrote. "Our analysis took advantage of the natural experiment opportunity by fluoridation cessation in the city of Calgary, Canada, which occurred in May 2011."

Water fluoridation may make a difference

For the study, McLaren and colleagues looked at data collected from second-grade children in Calgary and Edmonton. The cities were chosen because they are the two largest cities in Alberta, as well as diverse, urban centers.

They used data collected on children from the 2004-2005 school year and also created their own survey for the 2013-2014 school year. The earlier data consisted of population-based surveys of the two cities, and the researchers modeled their survey to match the previously collected information.

While McLaren and colleagues analyzed all primary teeth, they also focused on soft tooth structures, because the effects of fluoridation cessation is most likely to be evident on those structures. The researchers specifically defined smooth surfaces as all surfaces except occlusal surfaces and surfaces where pit and fissure caries commonly occur.

The researchers found a significant increase in primary teeth caries for children in both Calgary and Edmonton; however, the increase was greater in Calgary. The increase happened in all teeth, as well as smooth surfaces only.

Data courtesy of "Measuring the short-term impact of fluoridation cessation on dental caries in Grade 2 children using tooth surface indices," Community Dentistry and Oral Epidemiology, February 17, 2016.

However, the researchers did not find a significant increase in caries in permanent teeth for Calgary children. The researchers suggest this may be because the time frame of the study was short and because permanent teeth are structured differently than primary teeth.

"Based on knowledge of enamel differences between primary and permanent teeth, which make it likely that effects of cessation would appear sooner in primary teeth, we suggested that the absence of an increase in permanent teeth may have reflected the short time frame since cessation in our study," the authors wrote.

More research is needed

The authors suggested future research is needed to continue to monitor the effects of the community water fluoridation cessation in Calgary versus Edmonton. Notably, they are interested in seeing if the cessation will affect the resident's permanent teeth as time passes.

The authors also noted that community water fluoridation cessation may not be the cause of the caries increase. They indicate other reasons could include the recession in 2008, shifts in the Alberta economy, and an increase in ethnic diversity.

"Collectively, the literature indicates that the impact of fluoridation cessation on dental caries is not uniformly positive or negative but varies by time and place, and sorting out the reasons for different patterns is important," they wrote. "It is important that future data collection efforts in the two cities be undertaken, to allow continued monitoring of these trends."