A new study shows that tooth decay among Calgary children has gotten worse since the city took fluoride out of its water supply in 2011. Michael Conroy / AP The study compared the teeth of Grade 2 children in Calgary to those in Edmonton, where fluoride is still added to drinking water. While there was a general decline in dental health in both cities, the results were markedly worse in Calgary.University of Calgary researcher Lindsay McLaren, who is the lead author of the study, said the results show a clear cause and effect. “This study points to the conclusion that tooth decay has worsened following removal of fluoride from drinking water," she said in a releaseThe results were published in the latest issue of Community Dentistry and Oral Epidemiology. Fluoride is a naturally occurring element that, in small doses, helps prevent tooth decay. Helmut Seisenberger / Getty Images Water fluoridation is widely recommended by public health bodies, including the Canadian Dental Association, the Canadian Medical Association, and the World Health Organization. The U.S. Center For Disease Control and Prevention named it one of the "great public health achievements" of the 20th century.In recent years, however, cities across North America have removed fluoride from their drinking water following local campaigns questioning its safety. In 2011, Calgary city council voted 10–3 to stop adding fluoride to the water over the objections of numerous experts who spoke out against the decision, including the city's officer of health. Health Canada estimated that about 45% of Canadians had fluoridated drinking water in 2010. That number has dropped to "less than 30%" as of 2015, according to the group Canadians Opposed To Fluoridation. Thinkstock Since Calgary moved to defluoridate its water supply in 2011, more than two dozen Canadian cities have followed suit, including Saint John and Moncton in New Brunswick, and Prince George, B.C.