The purpose of this study was to develop a web-based method for testing dental students on the radiographic interpretation of approximal tooth surfaces. Part I involved the development and validation of an image editing method for transplanting approximal surfaces from one radiograph to another. Using this technique, histologically verified surfaces were transplanted into existing clinical radiographs and images were altered to change caries risk perception. In part II, the prototype of the testing module was administered to 80 third year dental students for competency assessment. This study validated the use of image editing and showed overall satisfactory class performance for radiographic caries interpretation. Substantial variations in sensitivity and specificity were noted, indicating the need for individualized teaching strategies for a subgroup of students. An increase in perceived caries risk increased the sensitivity and decreased the specificity of radiographic caries detection.