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The study, jointly conducted with researchers from the University of Alberta and Alberta Health Services, required open mouth exams of about 5,000 Grade 2 students in the two major cities. Investigators counted the number of tooth surfaces with signs of decay.

Those results, collected during the 2013-14 school year, were then compared with similar data gathered in 2004-05 to look for any changes over time.

Neither city fared well in the analysis, each recording increased rates of tooth deterioration. However, the worst results were in Calgary, where the number of surfaces with decay increased an average of 3.8 over the time frame of the study. In Edmonton, the increase was 2.1 surfaces.

A Grade 2 student has about 20 teeth — both baby and permanent teeth — with about four or five surfaces per tooth.

Steven Patterson, a professor of dentistry at the U of A who served as one of the study’s investigators, said the worsening trend in both cities is consistent with anecdotal evidence reported by dentists.

He said it is still unclear why dental health has been declining, especially since many products, such as toothpaste, contain fluoride.

Poorer nutrition is likely the biggest contributor, along with increased consumption of bottled water that contains little or no fluoride, he said.

“It’s also possible more people are not able to access dental care for some reason,” he said. “It’s hard to know definitively. But I suspect the big impact is related to what people choose to eat.”