ACCURACY OF QUANTITATIVE DIGITAL SUBTRACTION RADIOGRAPHY FOR DETERMINING CHANGES IN CALCIUM MASS IN MANDIBULAR BONE - AN IN-VITRO STUDY

The aim of this in vitro study was to determine the accuracy of digita l subtraction radiography (DSR) to detect small changes in calcium mas s in alveolar bone adjacent to tooth roots. In each of 4 dried porcine mandible segments, one interproximal and one buccal ''defect'' region was defined adjacent to a premolar root. A series of cortical and can cellous bone slices with a 50 mu m-stepwise increasing thickness (0-50 00 mu m) mere attached to the mandible segments covering the respectiv e ''defect'' region. Standardized radiographs were quantitatively asse ssed for density changes using DSR. After dissolving each bone slice i n hydrochloric acid, its calcium concentration was photometrically det ermined. For each bone slice, the mean calcium mass covering a single pixel of the subtraction image was calculated. The Wilcoxon signed-ran k test and the Mann-Whitney U-test were used for statistical analysis (alpha=0.05). A strong linear correlation (r(2)=0.86-1.00; p less than or equal to 0.001) was found between the thickness of the bone slices and their calcium mass. Cortical bone showed a 3.5 times higher mean calcium mass/pixel than cancellous bone. Furthermore, a strong linear correlation (r(2)=0.63-1.00; p less than or equal to 0.001) was found between the mean calcium mass per image pixel and the radiographic den sity changes. Neither the bone type nor the ''defect'' localization ha d a significant influence on radiographic density changes caused by ch anges in calcium mass. A change in mean calcium mass per image pixel o f 0.1-0.15 mg was necessary to be detected by DSR. In conclusion, this study revealed a high accuracy of DSR to detect small changes in calc ium mass in alveolar cortical and cancellous bone.