How does the direction of region of interest selection affect the fractal dimension?

OBJECTIVES: Introduction Fractal analysis (FA) is a computational method used to quantify the complex trabecular structure of bone. While FA has been widely applied in dentistry, there are challenges in standardizing the technique due to factors such as image resolution, region of interest (ROI) selection, and image processing. This study aimed to investigate the impact of the direction of ROI selection (DROIS) on fractal dimension (FD) calculations. METHODS: Panoramic radiographs of 226 individuals aged 20-35 years were analyzed. ROIs were selected on the mandibular condyle, angular region, and mental region, and oriented at 0 degrees , 22.5 degrees , 45 degrees , and 67.5 degrees angles. FD was calculated using the box-counting method in ImageJ. The Friedman test and Wilcoxon signed-rank test were used for statistical analysis. RESULTS: The FD values differed significantly between the angled ROI groups in all three regions (Friedman test, p < 0.0001). Pairwise comparisons showed significant differences in FD between most ROI orientations, except between 22.5 degrees and 67.5 degrees in the angular region. CONCLUSIONS: DROIS is an important factor that should be considered in FA studies to ensure reliable and reproducible FD values. Appropriate methodological choices can help account for the influence of DROIS on FD calculations..