May 13, 2015, 4:09 AM UTC / Updated May 13, 2015, 4:09 AM UTC / Source : NBC News

Virtually all American adults have tooth decay, and more than a quarter have cavities that have not been treated, a new government survey finds.

Americans may be known around the world for having strong, white teeth, but the dentist sees something different inside a patient’s mouth, the study from the National Institutes of Health and the Centers for Disease Control and Prevention finds.

“Approximately 91 percent of U.S. adults aged 20–64 had dental caries in permanent teeth in 2011–2012,” the report, published by CDC’s National Center for Health Statistics, finds.

By the time they hit 65, 96 percent of Americans have tooth decay, the survey found.

"It is not what people are doing wrong. It is maybe what we can do better," said Dr. Bruce Dye of the National Institute of Dental and Craniofacial Research, who led the study.

A lot has to do with access to dentists. People without health insurance coverage for dental care, or living in areas where dentists are not common, are more likely to have tooth decay, and far more likely to go without fillings.

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“The prevalence of untreated dental caries was nearly twice as high for non-Hispanic black adults (42 percent) compared with non-Hispanic white (22 percent) and Asian (17 percent) adults,” Dye and colleagues wrote.

They used a national survey of tens of thousands of Americans, called the National Health and Nutrition Examination Survey, for their report.

About 19 percent of people 65 and over have no teeth at all. This rises to 26 percent of people 75 and older.

This report looked at adults. A previous survey found 42 percent of kids aged 2 to 11 have tooth decay, and 23 percent had not been treated for it.

According to the American Dental Association, tooth decay is the most common chronic disease in children in the U.S., five times as common as asthma.

Caries, which comes from the Latin word for “rotten”, is caused mostly by bacteria reacting with sugar in the mouth. They produce acid that leaches minerals from the teeth and weakens them. So it’s an infectious disease — one that stays with people for life. Plus there is a genetic susceptibility to developing tooth decay, Dye said.

Fluoride helps slow this loss of minerals and greatly reduces rates of tooth decay. The CDC says 69 percent of Americans who use public water systems, or about 184 million people, get fluoridated water.

There's been a recent rise in the rate of cavities among kids, and dentists think the popularity of bottled water — which often isn't fluoridated — might be to blame.

Dentists had hoped a sweetener called xylitol might reduce the risk for tooth decay but a giant study recently found it didn’t.

Although most Americans have tooth decay, the situation is far improved from past generations, Dye said. Toothbrushing, fluoridation and better dental care have all helped, he said.