As I pointed out above, if you rinse with water after brushing your teeth, then you are rinsing away the benefits that fluoride provides to your teeth. Since most people only brush for somewhere around a minute, the fluoridated toothpaste doesn’t spend much time in contact with the teeth. By not rinsing out after you’re done brushing, you give the fluoride more time to protect your teeth, which could translate to healthier teeth with fewer cavities. This theory has been backed by research. Even rinsing with a tiny amount of water and making a mouthwash out of the toothpaste left in your mout after brushing has been shown to be effective. The textbook Dental Caries by Fejerskov states that “Clinical studies in which some of the participants have been taught to use a small volume of water and the toothpaste slurry left after brushing as a ‘mouthrinse’ have demonstrated that further reductions in caries are achievable. A 26% reduction in the incidence of approximal caries has...