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The number of children in Calgary with rotting teeth has jumped – both in comparison with a historical accounting of kids in the city and when stacked up against their counterparts in Edmonton – since Alberta's largest city stopped adding fluoride to its drinking water, according to a new study.

Calgary councillors voted to drop the fluoride program in 2011, while Edmonton's continues. Tooth decay for children in Grade 2 in Calgary climbed by an average of 3.8 tooth surfaces in the 2013-14 school year compared with the 2004-05 year, while increasing by 2.1 in Edmonton, according to a study by researchers at the University of Calgary.

About 45 per cent of Canadians drink fluoridated water, according to Health Canada, which says it is safe to add the mineral to water up to a certain concentration.

Canadians have been drinking fluoridated water for more than six decades, but the debate continues. Councillors in Ontario's Peel Region, for example, recently formed a committee to re-examine fluoridating. A resident of Terrace, B.C., last week presented local politicians with a petition signed by hundreds of people wanting to end fluoridating. Scores of cities have turned to plebiscites to make decisions on fluoride.

"We believe that the reason [the rate of tooth decay] got worse in Calgary than in Edmonton was because fluoridation was stopped," Lindsay McLaren, a professor and researcher in the department of community health sciences at the University of Calgary, said in an interview.

Her team's study was published in the Community Dentistry and Oral Epidemiology journal on Wednesday and in the International Journal for Equity in Health last week.

"An increasing number of municipalities across Canada are revisiting their fluoridation policy, and until now they had very, very little in the way of evidence on implications of cessation for dental health," Dr. McLaren said. She declined to make recommendations based on the study's findings, although elected officials in Alberta have already approached her. About 5,000 students participated in the 2013-14 survey, which was compared with data collected in 2004-05 school year.

While Dr. McLaren said Calgary's cavity problem is connected to its water, the results in Edmonton could reflect factors such as nutrition or socio-economic changes.

The study focused on baby teeth, although it did show an increase in decay on permanent teeth, she said. Though those results were not statistically significant, the researcher believes it is an early indication Calgary's water policy is also harmful for adults.

Calgary estimated it cost $750,000 annually to add fluoride to its water.

John Sprovieri, a councillor in Brampton, Ont., sits on the committee reviewing the area's fluoridation policy.

"I don't believe the municipal level should be the deciding level of government to mandate fluoridation," he said. The politician also questions whether the materials used to increase fluoride in the water supply are entirely safe. Fluoride itself, he argued, is dangerous when people ingest too much.

"It is right on your toothpaste [tube]," he said.

Calgary councillor Gian-Carlo Carra voted against fluoridation in 2011 because it should not be a municipal issue, and said his reasons have not changed.

"One hundred per cent it is a provincial issue," he said. "The province should deal with it."

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