CDC found these stats with two national health studies

The CDC's finding is based on the analysis of data from two national health studies in which the participants were interviewed and dental check up performed to assess the oral health. The first study on 26,000 U.S civilians was conducted from 1994-2004. The second study was conducted from 2004 to 2014 and included more than 25,000 participants. Data regarding the oral health from the two studies were compared to observe the pattern.