Snopes.com commented on the flossing evidence story and here's the conclusion from the closing paragraph:
"However, the decision to drop flossing from list of federal guidelines came not because there was solid evidence that it was ineffective, but because there was a dearth of non-anecdotal evidence — due to the ethical and practical considerations inherent in conducting a broad and long-term study on the practice — that flossing effectively prevents tooth decay and gingivitis."
http://www.snopes.com/2016/08/06/flossing-isnt-backed-by-science/
