Evaluation of digital and geometric unsharpnesses in dental radiographs

Recent advances in digital electronic devices have led to developments in digital radiography. Increased interest in imaging systems other than conventional filmbased radiography has been stimulated by anticipated reduction in patient radiation exposure with increased convenience and image quality. With the new imaging systems developing, it is necessary to evaluate the image quality with comparison to conventional film-based radiography. The aim of this study was to develop a definitive evaluation based on an endodontic file model for comparison of the effects of geometric and digital unsharpnesses in dental radiography. The endodontic file has a well-defined outline and small size, which makes it ideal to test resolution. Files of sizes 6, 8, 10 and 15 were placed in the root canal of an extracted lower incisor at 3 different positions with 2mm increments. Radiographs were taken at magnification factors of 1.0,1.1,1.2 and 1.3. Each radiograph was digitized at resolutions of 75, 150, 300 and 600 dots per inch (dpi). A digital visual analog scale was used for the assessment of image quality. Ten observers viewed the 192 digital images and identified the positions of the end of the files and the end of the root. Measured distances between these points were compared with a gold standard (actual file positions). Analysis of variance and paired T-tests were used to demonstrate significant differences. No significant differences were found between the resolutions of 300 and 600 dpi, nor between the magnifications of 1.0 and 1.1. Significant differences were found between the magnification of 1.3 and the others, and the resolution of 75 dpi and the others, for all the files. The effects of geometric unsharpness within the range studied for all the file sizes were not significant except for the magnification of 1.3, which is of little clinical relevance. Based on this study, with endodontic files in an extracted tooth, there is little need for resolutions higher than 300 dpi in clinical dental radiography and geometric unsharpness has no influence on diagnostic information. This may apply to many other aspects of diagnostic imaging.Dentistry, Faculty ofGraduat