Intra-oral and extra-oral digital imaging:: an overview of factors relevant to detector design

Since the introduction of the first intraoral detector system 15 years ago, major improvements have been achieved. Initially, fibre optic coupling was used between the entrance phosphor and the small CCD sensor, later sensors became available for direct exposure. Also the dimensions of the active area were increased to comply with the size of analogue dental films and the thickness of the sensor was decreased. Intraoral films are flexible, CCD-type sensors however, are stiff and therefore much more difficult to position in the mouth of the patient. The resolution of modern intraoral sensors is comparable or even higher than that of film, but with increasing resolution, noise is becoming a problem in some diagnostic tasks. maging phosphor plates and CCD-based systems are also used in extra oral imaging. The procedures in phosphor plate technology are quite comparable to those of conventional film. As the width of CCD sensors is limited, a slit imaging technique is used in panoramic imaging and still images. Tomography, a radiographic method to display layers within an object is not possible with the present CCD sensors.