An in-vitro evaluation of a dental subtraction radiography system using bone chips on dried human mandibles

The aim of this in vitro study was to evaluate the ability of digital subfraction radiography to detect small differences in bone density between 2 dental images captured with the Digora(R) radiographic imaging system. 5 dried human mandibles were held in a fixed position and cortical bone chips were superimposed on the alveolar bone between the 1st molar and 2nd premolar teeth. For each mandible, a reference image was obtained without bone chip placement. Subsequently, another image without a bone chip and a series of 10 images with bone chips ranging from 1.2 to 35.3 mg, were recorded. Each of the initial images of the 5 mandibles was then compared to the 11 subsequent images using digital subtraction radiography. The difference in density between the 2 images, at the site between the Ist molar and 2nd premolar, was calculated and represented as a volume equivalent of aluminium. Regression analysis demonstrated a close relationship between the weight of the bone chips and the aluminium equivalent density difference between the 2 radiographs (r(2)=0.96). Good results were obtained with the smaller bone chips that more closely resembled the dimensions of bone changes likely to be of clinical interest (1-8 mg). It is concluded that this subtraction radiography system is suitable for clinical investigations of localised small changes in alveolar bone and for the diagnosis and monitoring of destructive forms of periodontal diseases.