[Dosimetric evaluations in dental radiology: comparison of the digital system and the conventional system]

The dosimetric values measured on digital dental examinations (panoramic radiography and cephalography) were compared with those obtained with screen-film combinations. The X-ray dose was measured at the critical organs (lens, thyroid, cervical cord) on an anthropomorphic phantom, using thermoluminescence dosimeters and an ionization chamber: the radiographic unit was set at the same exposure values used for standard human studies in adults and children. The mean thyroid dose for screen-film panoramic radiographs was 0.037 mGy in the child and 0.053 in the adult; the lens and the cord doses were 0.009-0.012 mGy and 0.096-0.135 mGy, respectively. Digital panoramic radiography gave the thyroid a dose of 0.013 mGy in the child and 0.016 mGy in the adult: such a marked dose reduction was observed for the lens and the cervical cord too (0.0044-0.0052 mGy and 0.035-0.042 mGy, respectively). With conventional film cephalography the thyroid was given a mean dose of 0.042-0.072 mGy according to age and to patient's size; the lens received higher doses (0.420-0.720 mGy). These values were markedly reduced with the digital technique; 0.032-0.034 mGy to the thyroid gland and 0.320-0.340 mGy to the lens; spinal cord doses became negligible with digital exposures (0.009-0.010 mGy). The overall analysis of dosimetric values demonstrated a mean dose reduction averaging 40-60% with respect to standard film exposure. This difference is more apparent in the adult, since the linear dose-response pattern of the digital system allows good images to be acquired in "thicker" people without markedly increasing exposure values.