Approximal caries depth assessment with storage phosphor versus film radiography. Evaluation of the caries-specific Oslo enhancement procedure.

OBJECTIVES: To study whether caries-specific enhancement of storage phosphor images might improve the observer performance of approximal caries depth assessments compared with film radiography.
MATERIALS AND METHODS: 120 exposures were made of 120 extracted human teeth. To obtain geometrically identical images, Ektaspeed Plus films and storage phosphor plates were exposed simultaneously. The imaging plates were scanned in a Digora scanner and the files transferred to a different platform for image enhancement. Nine observers viewed films and storage phosphor images without provisions for adjustment of image intensity and contrast. For each imaging modality, 240 approximal surfaces were rated for caries on a 5-point confidence scale. Definite and probable caries lesions were also rated for lesion depth, and all ratings were compared with the histological state. Diagnostic accuracy was expressed as the area under the ROC curve (A(z) value). Paired t tests were used to compare the imaging modalities for diagnostic accuracy and F tests to compare observer variances.
RESULTS: Enhanced storage phosphor images demonstrated significantly higher mean A(z) values than film (p = 0.0066). Significantly higher mean A(z) values were demonstrated in the outer half of enamel (p = 0.01), but no significant differences were found between the modalities for caries lesions penetrating beyond the outer half of the enamel. The number of correctly diagnosed true-positive surfaces with caries in outer enamel was significantly higher with storage phosphor images than with film (p = 0.00014). False-positive surfaces were most frequently registered in the outer enamel with both modalities, but in this region the number of false-positive surfaces was significantly higher with storage phosphor images than with film (p = 0.0038). Pooled sensitivity and specificity values were 0.48/0.94 and 0.61/0.86 for film and storage phosphor images, respectively. The interobserver variability was significantly lower for storage phosphor images than for film.
CONCLUSION: Enhancement of storage phosphor images with a caries-specific procedure significantly improved the accuracy of caries depth assessments in the outer half of the enamel compared with film radiography and reduced observer variability.