Summary statistics of the data published by H T Dean in 1943, on the naturally occurring fluoride levels for 21 communities in the USA, based on average number of permanent teeth per child in each location affected by dental caries is given below. x (fluoride concentration) = 14.55 x2 (fluoride concentration) = 21.2675 x (fluoride concentration) y (number of teeth)= 45.31 y (number of teeth) = 111.7 y2 (number of teeth) = 719.09 xy = 45.31