In the growing debate about fluoridating Portland's drinking water, one news agency has dug out data the state of Oregon didn't want to release, and the reporting raises questions about the overall effectiveness of adding fluoride in Portland.

KATU Channel 2 pressed the state Oregon Health Authority for weeks to release data from its 2012 Smile Survey, a review of dental health involving thousands of Oregon school children. KATU's Shellie Bailey-Shah reports the state held on to the data even as the debate about fluoridating Portland's drinking water raged.

In the May 21 election, Portland voters will decide on Measure 26-151, which would require the city to fluoridate its water supply. Portland is the nation's biggest city not to add fluoride, which health experts say improves the dental health for children.

Among the findings revealed through KATU's public records requests: children in areas with fluoridated water show little difference in the number of cavities they suffer, compared to Portland. As Bailey-Shah reports:

"You'd think the kids with fluoridated water would fare better. But in the Problem Solvers’ analysis, the results were nearly the same: 53.7% of the kids in the non-fluoridated areas had one or more cavities 52.03% of kids in fluoridated areas had one or more cavities 47.81% of kids in the Portland water district (which is currently fluoride-free) had one or more cavities."