ENVIRONMENT AND SHEDDING OF DECIDUOUS TEETH, ERUPTION OF THE PERMANENT TEETH, AND MORBIDITY OF DENTAL DECAY IN SCHOOL CHILDREN

Four places differing with respect to natural and social environment, (1) a city, (2) a suburb (3) a mountain village and (4) three small islands in Yamaguchi Prefecture were chosen and numbers of the remaining deciduous teeth and erupted permanent teeth, dental decay (def and DMF) in 7382 children of primary and junior high schools were investigated and compared. 1. Exchange of the teeth occurs most early in the urban district, then the suburb, mountain village and islands in the ordor. 2. In every district, the eruption of permanent teeth is earlier in girls than in boys, and it is earlier in the lower jaw than in the upper except the premolar. 3. The shapes of frequency distribution of number of the remaining deciduous teeth change from J-type to Poisson-type, symmetric and L-type as the age advances from 6 to 15 years : those of the erupted permanent teeth are quite contrary to the above. 4. The dental decay expressed in def and DMF is highest in the city and declines in the order of the suburb, mountain village and islands.