VALIDATION OF QUANTITATIVE DIGITAL SUBTRACTION RADIOGRAPHY USING THE ELECTRONICALLY GUIDED ALIGNMENT DEVICE IMPRESSION TECHNIQUE/

THE ELECTRONICALLY GUIDED ALIGNMENT device (EGAD) has been demonstrate d to function well with a custom fabricated stent for taking radiograp hs for subtraction. The objective of this study is to demonstrate that this device functions well when used with an impression bite-block ra ther than a full arch acrylic stent. Nineteen subjects participated. T wo vinyl siloxane impressions were made for each subject and a pair of x-rays was taken with each impression. The location for study was div ided among 7 for the maxillary premolar-1st molar region, 6 for the ma ndibular premolar-1st molar region, and 6 for the incisor-canine regio n. To simulate bone change 3 bone chips (approximately 1, 7, and 10 mg ) were positioned in the mucobuccal fold when one of each pair of x-ra ys was taken. Pairs of radiographs were subtracted and the bone change (chips) isolated by thresholding to determine their area. An aluminum ramp was used to determine volume. A strong linear relationship betwe en actual chip weight and equivalent aluminum volume (r(2) = 0.64, P < 0.001) was obtained for all regions of the mouth when considered toge ther. The strongest relationship of the 3 regions was for mandibular p remolar-1st molar sites, r(2) = 0.78. These data indicate that the EGA D/impression technique is suitable for taking radiographs in all areas of the mouth for quantitative digital substraction.