Unlike our toothpastes, Pepsodent didn't contain fluoride or appropriate cleaning agents. Its vaunted "clean" feeling was produced by an abrasive ingredient that was, according to one Columbia University chemist who tested it, "hard and sharp enough to cut glass." Furthermore, he found that "Mucin placque [technical term for the 'film'] cannot be digested from teeth by any advertised use of 'Pepsodent.' " Another problem was that Pepsodent's initial success had lured in competitors, so that there were more than one hundred brands of toothpaste on the market by the late 1920s.

Tim Wu, The Attention Merchants, loc. 288