FACTORS AFFECTING THE INCIDENCE OF DENTAL CARIES IN POPULATION GROUPS

¹ Department of Experimental Medicine, University of Cincinnati

In a general way the survey data show the following points. First, the incidence of caries in American school children increases steadily throughout the United States as the distance from the tropics increases. This trend is in evidence in both rural and urban populations. Its probable relation to sunlight intensity is further supported by the presence of less caries in the northern Plains states, where sunlight is more plentiful than in other northern areas. Second, there are indications of diminishing caries incidence as one passes from the mouth of a river toward its head waters, a phenomenon that may be related to soil leaching. Third, there is an inverse relationship between drinking water hardness and caries incidence, cities using river water showing about 30 per cent more caries than do cities using well water. Fourth, there is a direct relationship between caries incidence and amount of salt used in seasoning food. Fifth, negro children in all areas show less caries than do the white, but the same regional relationships obtain.

Tooth decay shows certain definite relationships to extrinsic factors. It is related to latitude, increasing steadily toward the north within the United States. This is probably related to the known beneficial action of ultraviolet light in promoting tooth and bone formation and repair. Caries is also related to hardness of city drinking water, and to dietary salt intake. It is suggested that the high caries incidence of mining regions may be due to the sulphuric acid seepage from the mines into the water used for drinking purposes. The possible rôle of sulphur oxides liberated in coal burning may likewise be a factor tending to increase caries, due to the absorption of these oxides in the lungs and their action as fixed acids on the mineral metabolism of the teeth.

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