Evaluation of automatic exposure control in a direct digital intraoral system

The aim of this study was to evaluate the performance of the automatic exposure control (AEC) in an intraoral digital system.

Three series of radiographs were captured with the activated AEC on seven dry mandibles adhered to different thicknesses of Plexiglas((R)), which represented soft tissue. Exposure times required for each radiograph of the specimens were analysed as functions of the added Plexiglas thickness. Differences in mean grey levels between pairs of the three images obtained from the same specimen were analysed by employing the subtraction technique. Additionally, four radiographs of all seven mandibles were manually exposed with one layer of Plexiglas, which employed one and two steps below and above the registered automatic exposure time. Six observers evaluated the series of radiographs exposed with one layer of Plexiglas in a random order. The observers were instructed to classify the quality of the diagnostic images as unacceptable, acceptable or excellent.

The results demonstrated a good correlation between the exposure times determined by AEC and Plexiglas thickness (r = 0.85). Mean grey level values for subtraction images obtained from radiographs exposed with different thickness of Plexiglas with activated AEC indicated that almost identical radiographs were obtained, regardless of the Plexiglas thickness. The subjective observer evaluation of the most satisfactory radiographic image quality as a function of exposure time demonstrated that the highest scores were for radiographs exposed with the AEC function activated.

The AEC function may accurately determine the appropriate exposure times related to object thickness, providing radiographs with satisfactory image quality, and may thus be advantageous in clinical radiographic work.