When an orthodontist asked the reporter if he wanted a good story idea, the reporter, of course, said "yes."

Jeff Donn, a national writer with The Associated Press and 2012 Pulitzer finalist, was doubtful, at first, about that tip from his son's orthodontist: There's no solid evidence that flossing actually works.

"But when I started to look at research, I realized that it was a good tip — and definitely the best one I ever got from an orthodontist."

As a reporter who's covered the dangers of aging nuclear power plants, drug safety and abandoned oil wells, Donn was attracted to the floss story because it seemed so easy for people to grasp, he said.

It also ended up having a big impact.

After lots of research and a FOIA request, his inquiries caused a change in government guidelines recommending flossing. He spoke with Poynter via email about how the story developed, what the response has been and whether he's still flossing.

Tell us about the process behind this story. It started with a FOIA, right?

My work started with a careful look at the research. Much of it was identified in five medical literature reviews undertaken over the past decade. I also began to wonder how floss had gained such wide acceptance, who had promoted it, and why.

I found that the federal government had been promoting floss for decades, chiefly in its Dietary Guidelines for Americans. By law, the guidelines must be based on science, so I asked staffers at the responsible agencies — the departments of Health and Human Services and Agriculture — for the documentation behind the floss recommendation. Weeks of requests failed to turn up anything. So I filed a formal FOIA request.

Six months passed. On Jan. 7, the government put out a new edition of the guidelines, as scheduled. The flossing recommendation had quietly been dropped. The next day, HHS wrote a letter to me in reply to my FOIA request. It said that no relevant records could be located and then added that floss had never been researched by the committees that review science for the guidelines.

It said that flossing had simply been taken as a "general public health recommendation." In the end, this appeared to be a rare instance where simply filing a FOIA changed government policy.

When the government left flossing out of the latest dietary guidelines, was that the first time you knew they'd made the change? What happened next?

Yes, I only discovered the omission in reading the new guidelines. I then called HHS to ask what happened. They referred me to Tim Iafolla, the quoted NIH dentist who acknowledged the poor evidence but suggested that people should floss anyway.

I listened to this story Tuesday afternoon on NPR and thought, 'Whoa, the AP just took down flossing.' What's the response to the story been?

The story appeared on more than 150 news websites. I stopped counting. Some other news outlets, including The New York Times and "NBC Nightly News", did their own matchers, duly crediting the AP for breaking the story.

I was interviewed by several radio stations, including some that did call-ins from listeners. Blogs and social media sites were buzzing. [Gizmodo] called the story a "monumental revelation." Lots of people had fun with this, too. A post on Actuarial Outpost, a social networking site for actuaries (no kidding), said: "I'm gonna tell the hygienist to get off my a — about it until she performs a peer-reviewed, double-blind study."

An especially gratifying reaction came from a professor at a college of dentistry, who thanked me for the story, saying the weak evidence for flossing’s benefits had long been a pet peeve for him, especially since it wasn't openly acknowledged by his profession. Dozens of colleagues from around the AP and the broader news industry — and other folks who simply read the news — contacted me to say they loved the story.

Many conveyed stories about themselves or spouses who either do or don't floss. Their most frequent question was how I came up with the idea.

What tips do you have for other journalists about pursuing big and impactful work?

Question everything, including if your mother really loves you.

Do you floss?

Yes, I still do — to remove annoying bits of foods stuck in my teeth. My wife yells at me when I use my finger or a fork. But I think the best science indicates that I’m not doing anything beneficial for my health.