The aim was to investigate to what extent an extension of the caries criterion into the dentin, may influence the need for therapeutical intervention. Using a computerized technic, the depth of all approximal lesions in posterior teeth in 151 persons, aged 20 and 23 years, were measured on magnified (x5) radiographs and expressed as per cent of the enamel width. The proportion diseased 20 year old persons was 88% if the criterion was any sign of caries but only 50% if the criterion was at least one lesion, reaching the dentin. When caries was defined as a lesion having a depth, corresponding the double enamel width the figure was 11% and the proportion surfaces in need of therapeutical treatment constituted 2% of the total caries volume. It is concluded that an extension of the filling criterion into the superficial layers of the dentin may reduce the need for filling therapy in 20 year old persons to a very low level.