This bottle of Crest Pro-Health says that it gives you 24-hour protection. Then it says that you should use it twice a day. So one swish protects you for a whole day, but just to be sure, you should swish twice. (Thanks to aweirdguy!)
Founded in 2005, Consumerist is an independent source of consumer news and information published by Consumer Media LLC, a not-for-profit subsidiary of Consumer Reports.