Abstract
This pre-liminary report describes the examination criteria for dental caries and methods in use and defines the population under observation in a continuing study of oral health in elementary and junior high school children of Montgomery and Prince Georges Counties, Md. The 2 counties are adjacent to the District of Columbia. The domestic water used by these children was fluoridated with sodium fluosilicate late in December of 1951. Evidence is presented that there was a statistically valid decrease of roughly 20% in the number of permanent teeth becoming carious during the 2d year of fluoridation, judged by findings from the baseline examination early in 1952.