Fluoridated toothpaste came about as the result of a discovery made in Naples, Italy in 1802, when local dentists noticed yellowish-brown spots on their patient's teeth - but no cavities. Subsequent examination revealed that high levels of fluoride in the water caused the spots and prevented tooth decay, and that less fluoride protected teeth without causing the spots. It took a while for the discovery to be implemented; the first U.S. fluoridated water tests didn't take place until 1915, and Crest, the firth toothpaste with fluoride in it didn't hit stores until 1956.