In two groups of patients, differing in caries prevalence, the restorative treatment of posterior approximal surfaces in permanent teeth was studied in radiographs obtained as part of the dental care provided from age 6 up to and including age 18. The study determined at what age, at which lesion depth and in which surfaces restorative treatment was performed. Furthermore, the conditions of nonrestored dentin lesions were evaluated over time. Nearly 50% of the restorations were placed in the mesial surface of the first molars. In both groups more than 2/3 of the restorations were placed in surfaces with dentin lesions. In the group with the highest caries prevalence 50% of the lesions in the outer half of the dentin were restored when first detected in contrast to 20% in the groups with the lower prevalence. For the superficial dentin lesions not immediately restored, average time between their detection and restoration, the end of the study or, detection in the inner half of the dentin was practically the same in both groups (19.3 and 20.4 months). The variation in this average time was only to a limited degree explained by the variation in the caries experience of the patients.