The effect of exposure reduction on the diagnosis of caries: An ex vivo comparison of film and a CMOS digital imaging system

Objectives: To determine the effect on caries diagnosis of exposure reduction on intraoral digital radiographs compared with optimally exposed film images. Materials and Methods: F-speed film radiographs of 61 extracted molars and premolars were made with optimal exposure parameters. The teeth were radiographed using a complementary metal oxide semiconductor (CMOS) digital system with exposures equal to 50%, 30%, 20%, 10%, and 5% of the film exposure. Five observers, who were permitted to adjust brightness and contrast on the digital images, scored the proximal and occlusal surfaces for the presence of caries using a 5-point confidence scale. Areas under receiver operating characteristic (ROC) curves represented accuracy of caries detection. Sensitivity and specificity were also calculated. The significance level was P = 0.05. Results: All digital images resulted in lower diagnostic accuracy than film images for all lesions (P ≤ 0.036) and for caries in enamel only (P ≤ 0.030). With dentin caries, there were no significant differences between film and any digital radiographs (P ≥ 0.065) except the 5% exposures (P ≤ 0.034). Digital radiographs of 5% of the exposure of film were significantly poorer than all other exposure categories (P ≤ 0.014) except for the 10% exposures for accuracy for all lesion sizes and for dentin lesions only. Exposures at 10% and 20% resulted in lower sensitivity scores for enamel caries, while 50% exposures were associated with the poorest specificity. Conclusions: Exposures of 30% of optimal F-speed film exposure settings appear to balance acceptable levels of accuracy, sensitivity, and specificity for caries detection. Observer-controlled enhancements were ineffective at extremely high and low exposures