A method to evaluate and compare two different intraoral radiographs of the same patient

Objective of this study was to determine the accuracy of the method of the clinical intraoral densitometry, to compare differences in the calculation with or without subtraction of the background adjacent soft-tissues from the stepwedge (SW) and to verify which regression model best fitted the experimental data in order to express the measured values in equivalents of SW thickness. Two intraoral radiographs, one after another, were made for each of 6 patients. A copper SW (6 steps, thickness 0.05-0.3 mm) was attached to each radiograph, trying to avoid the superimposition of the bony structures. Films were processed and digitized. Grey levels were measured on each step of the SW, on the background of the SW and on the same 3 randomly chosen regions of interest (ROIs) on each digitized image. The measurement with and without the subtraction of optical densities of the background around the SW from the optical densities of the SW was performed. For the calculation of the SW thickness equivalents, the regression analysis was performed by using different regression models. The best fitting regression model was the 3rd degree polynomial. The results were more precise when using the subtraction of the background overlapping the SW.