Orthodontic radiographic procedures--how safe are they?

Parents of children subjected to radiographic procedures for orthodontic purposes occasionally express concern about possible radiation overdose to sensitive structures in the head and neck region. The following study was designed to determine this. Twenty Harshaw lithium fluoride thermoluminescent dosimeters (TLDs) were irradiated using a calibrated RT 100 X-ray source. These were read in a Toledo 654 TLD reader. The readings of all dosimeters fell within 10% on either side of the mean reading for the dosimeters. Twelve were finally selected which fell closest to the mean. Six of the TLDs were randomly selected and placed in a Rando female phantom in a position corresponding to the lens of the eye-3 in the left and 3 in the right eye. A standard pantomogram was taken of the phantom using an Orthophos machine. The TLDs were then replaced by another two groups of 3 in the same positions in the phantom and a lateral cephalogram taken on the same machine. The TLDs were read in the Toledo reader. Six of the 12 TLDs were then randomly selected for re-use. Three were placed in the phantom in the region of the thyroid and a pantomogram again taken. The procedure was repeated for a cephalogram and the TLDs again read. In all cases the readings of each group of 3 TLDs did not vary by more than 10% on either side of the mean readings. The TLD readings were then converted by means of a conversion factor to actual dose measurements. The doses to left and right eyes and to the thyroid were respectively found to be 0,0151, 0,0222 & 0,0896 mSv for the pantomogram and 0,0351, 0,0183 & 0,0177 mSv for the cephalogram--an almost insignificant dose in terms of the "background equivalent" concept.