Effect of Image Enhancement Filters on the Detection of Periapical Radiolucent Lesions on Panoramic Radiographs: A Multi-Reader Multi-Case Study

Background: Panoramic radiography is widely used in dental practice, but its two-dimensional projection geometry and anatomical superimposition can obscure periapical radiolucent lesions, particularly in the maxillary anterior region and for novice observers. Methods: This retrospective multi-reader, multi-case study aimed to evaluate the effects of unsharp mask and Gaussian blur filters on the diagnostic performance and interobserver agreement of novice observers in detecting periapical radiolucent lesions on panoramic radiographs. Twenty final-year dental students evaluated 56 panoramic radiographs (28 lesion-positive and 28 lesion-free cases; 224 maxillary anterior teeth) under three imaging conditions (original, unsharp mask, and Gaussian blur). Observers scored lesion presence using a five-point confidence scale. Diagnostic performance (AUC, sensitivity, and specificity) was compared using the Dorfman–Berbaum–Metz/Obuchowski–Rockette multi-reader, multi-case method. Interobserver agreement was assessed using quadratic-weighted Cohen’s kappa and the intraclass correlation coefficient (ICC). Results: Imaging condition significantly affected AUC, sensitivity, and specificity (all p ≤ 0.003). Compared with original images, unsharp mask significantly improved sensitivity (78.2% vs. 52.5%), specificity (90.2% vs. 83.2%), and AUC (0.876 vs. 0.737) (all p < 0.05), with the highest interobserver agreement (ICC = 0.951; κ = 0.476). Gaussian blur significantly reduced sensitivity (40.2%) and AUC (0.655) compared with original images (both p < 0.001). Conclusions: Unsharp mask filtering was associated with improved diagnostic performance and interobserver agreement among novice observers, whereas Gaussian blur was associated with reduced lesion detection performance. These findings suggest that unsharp mask filtering may have potential as an adjunct to radiographic interpretation training.