EFFECT OF EXPOSURE TIME ON IN-VITRO CARIES DIAGNOSIS USING THE DIGORA(R) SYSTEM

The aim of this study was to determine the in vitro diagnostic perform ance for approximal caries and occlusal dentine caries diagnosis of th e Digora(R) system for digital radiography in relation to the exposure time. Radiographs were made of 220 extracted human posterior teeth an d cuspids at exposure time levels of 3%, 6%, 10%, 20%, and 78% of the exposure time needed for E-speed film (image sets I, II, III, IV, and V, respectively). The image sets were put in random order (III, I, IV, II, V) and assessed independently by 3 observers using a 5-point conf idence scale. True caries status was determined histologically after s ectioning of the teeth. Evaluated parameters were: interexaminer kappa , sensitivity, specificity, D-z3/4(the distance of one operating point to the diagonal in the ROC domain) and area under the ROC curve. The Spearman correlation coefficients between the parameters and both expo sure time and order of viewing of the sets were calculated. For approx imal surfaces, the ranges of mean parameter values were: sensitivity 2 6-33%, specificity 93-95%, D(z3/4)0.63-0.84, area 0.61-0.69. For occlu sal surfaces, the ranges were: sensitivity 52-60%, specificity 91-95%, D(z3/4)1.03-1.34, area 0.79-0.87. Out of 24 pairwise comparisons betw een sets V and I, 5 were significant. Out of 24 comparisons between se t V and II, only 2 were significant. It was concluded that diagnostic performance is unlikely to be impaired for an exposure time as short a s 6% of E-speed him exposure. When reducing the exposure time to 3% of E-speed film exposure, caries diagnosis may be impaired.