Optimal Exposure Time for Diagnosis of Approximal Caries Lesions on Digital X-rays

In digital radiography the image can be enhanced and thereby an incorrect exposed radiograph can appear to have optimal brightness but with limited information and possibility to diagnose e.g. caries. The primary aim of this study was to determine if different exposure times have an impact on the accuracy in diagnosis of approximal caries lesions in bitewing radiographs using a CMOS system. If so, what the optimal exposure time was. A total of 40 extracted human teeth were selected and evaluated with a digital CMOS system. The teeth were exposed with different exposure times. CBCT was used to validate the presence and degree of approximal caries lesions on every individual tooth surface. The radiographs were evaluated by 11 general dentists and 4 specialists in oral and maxillofacial radiology. The choice of exposure time did affect the diagnostic accuracy. A higher diagnostic accuracy was achieved when a longer exposure time (> 0.1 sec) was used when comparing kappa values and ROC curves among the observers. The radiologists had a higher diagnostic accuracy than the general dentists. A substantial variation in individual diagnostic accuracy between observers was found. In conclusion; approximal caries was found to be easier to diagnose when the evaluated longer exposure times were used in the studied digital CMOS system. There was some decline in the longest exposures of the time span. However, when selecting optimal exposure time the patient's age and size should also be taken into consideration.