Effect of digital filtering on the measurement of the depth of proximal caries under different exposure conditions

Abstract

Purpose: To compare different image processing modes (filters) on the reproducibility and accuracy of the assessment of proximal carious lesions viewed in direct digital radiographs. Variables studied were exposure time and tissue scatter radiation.

Methods: Standardized direct digital radiographs of 50 extracted teeth were obtained and 44 areas of proximal caries were detected histologically. Four radiographs were obtained of each tooth using a charge coupled device sensor. Two radiographs were obtained with and two without tissue scatter radiation equivalent (TSRE) each of them at normal exposure time (0.06 second) and underexposed (0.01 second). On each of the 200 radiographs, the central depth (CD) of each carious lesion was measured at 21-fold magnification both on the unchanged image and after use of two different filters (median, median plus inversion). All measurements were repeated after 1 week to estimate reproducibility. Histometric CD assessments provided a gold standard for comparison with the radiographic measurements (accuracy).

Results: Whereas reproducibility was not influenced significantly by any of the investigated parameters, defect type and exposure time influenced the overall accuracy of CD measurements. Basic digital filtering of radiographic images failed to result in statistically significant improvement of the accuracy of CD measurements.