For decades, the federal government — not to mention your local dentist — has insisted that daily flossing is necessary to prevent cavities and gums so diseased your teeth fall out.

Turns out, flossing may be overrated.

The latest dietary guidelines for Americans, issued by the departments of Agriculture and Health and Human Services, quietly dropped any mention of flossing without notice. This week, The Associated Press reported that officials had never researched the effectiveness of regular flossing, as required, before cajoling Americans to do it.

It’s been an open secret among experts that flossing hasn’t been shown to prevent cavities or periodontal disease.

A review of 12 randomized controlled trials in The Cochrane Database of Systematic Reviews in 2011 found only “very unreliable’’ evidence that flossing might reduce plaque after one and three months. Researchers could find no studies on the effectiveness of flossing combined with brushing for cavity prevention.