THE EFFECT OF VARYING THE REGION OF INTEREST ON CALCULATIONS OF FRACTAL INDEX

Objectives: To compare the effect of using regions of interest (ROIs) of different size and shape on the fractal index of alveolar bone. Stu dy design: Two sets of clinical posterior bitewing radiographs were us ed to calculate the fractal index (S). Two comparisons were made. Firs t, S was calculated from large interdental ROIs that included small am ounts of root structure and compared with S from small ROIs that inclu ded no root structures. Then S was calculated from large interdental R OIs (similar to those used for the first set) and compared with S calc ulated from ROIs that included nearly all of the mandibular alveolar b one (and adjacent root) present on the bitewing. Results: For the firs t comparison, paired t-tests showed that fractal indices calculated wi th the large ROIs were significantly different from the respective ind ices calculated from the small ROIs (P<0.001). For the second comparis on, the fractal indices calculated from the large quadrant ROIs were n ot significantly different from those calculated from the large ROIs ( P = 0.120). Conclusion: ROI size and shape may affect the results of f ractal analysis of alveolar bone.