Objectives: To test the null hypotheses, that no differences are to be expected regarding the perceptibility of small, regularly shaped contrast details in film - based dental radiographs compared to their digitized counterpart and to direct digital images. Methods: An aluminum stepwedge (6 steps, thickness:3.00 - 8.00 mm) containing 19 bur holes (diameter: 1.00 mm, depth: 0.05 mm - 0.30 mm) was radiographed on an optical bench under identical conditions in two different modalities: radiographic film (F) and a ccd-receptor (D). The two images showing maximum contrast (F: 1.0s, 60kVp; D: 0.32s, 60kVp) based on the anonymous decision of two examiners were selected. The radiographic film was also digitized (S) on a ccd-flatbed scanner at 300 dpi. Both the digital and the film radiograph were separated into 23 single images each, 19 of which showed one dark spot representing a hole. Viewing conditions were standardized and equalized between digital (17"CTR monitor) and conventional (viewing box) mode. 30 observers had to state their decision twice on a five point confidence scale for each image as to whether or not a hole is visible. Receiver operating characteristic (ROC) curves were obtained from each observer and modality and areas beneath the curves (Az) compared between modalities using the sign test for paired data. Results: Mean Az was 0.77 for D, followed by 0.71 for F and 0.61 for S, with the differences between the modalities being significant on a confidence level of 0.05. Particularly in dark images (6th step of wedge: 3.00 mm) S yielded considerably lower sensitivity (0.39) than D (0.76) and F (0.72). Conclusions: Perception of small spots within a homogenous background was best for direct digital radiographs, followed by film -based and digitized images. The latter yielded a significant loss in sensitivity particularly in images with high optical density.

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