Variations between dentists in treatment thresholds and diagnostic decisions based on radiographs have not been fully explained. Since variations have been shown to exist between as well as within countries, it is possible that the structure of incentives inherent in different health care systems, and cultural influences on health and health care may play a part. This paper compares the results of a study undertaken in Scotland with a replication study undertaken in Canada concerning dentists' restorative thresholds and treatment decisions based on radiographic evidence. The Canadian dentists operated with greater sensitivity but lower specificity than their Scottish counterparts, although ROC analysis indicated similar overall abilities to detect carious lesions. The dentists' action thresholds also differed. However, methodological issues mean that the data from the study need to be interpreted with caution.