CBCT-based submandibular fossa depth classification and panoramic fractal dimension analysis in the posterior mandible

Deep concavities of the submandibular fossa (SF) in the posterior mandible substantially increase the risk of lingual cortical plate perforation during implant placement. Although cone-beam computed tomography (CBCT) enables accurate three-dimensional assessment of SF morphology, panoramic radiography remains the most commonly used initial imaging modality. We investigated whether trabecular bone texture on panoramic radiographs, quantified using fractal dimension (FD), is associated with CBCT-measured SF depth. In this retrospective cross-sectional study, 133 patients with CBCT and panoramic radiographs obtained within 3 months were included. SF depth was classified as Type I (≤ 2 mm), Type II (2–3 mm), or Type III (> 3 mm). On the matching panoramic level, a 20 × 20-pixel cancellous region of interest was analyzed in ImageJ using box-counting FD. Group comparisons were performed using the Kruskal–Wallis and Mann–Whitney U tests with Bonferroni correction; correlations were assessed using Spearman’s rank correlation coefficient (p < 0.05). A total of 229 hemimandible measurements were evaluated. Mean age was 41.96 ± 15.59 years; 57.1% were female. Mean SF depth was 1.845 ± 0.750 mm and mean FD was 1.0964 ± 0.0667. Median FD was 1.0747, 1.1324, and 1.1340 in Types I, II, and III, respectively (Kruskal–Wallis p = 4.45 × 10⁻⁵). FD was significantly higher in Types II and III versus Type I (p = 0.000514 and p = 0.00633), with no difference between Types II and III (p = 1.00). SF depth positively correlated with FD (Spearman rho = 0.4138, p = 6.95 × 10⁻¹¹). Panoramic FD values reflected CBCT-defined SF depth categories, with deeper concavities showing consistently higher trabecular texture complexity. These results suggest that SF anatomical variation is a previously unrecognized source of regional FD heterogeneity in the posterior mandible and should be considered when interpreting panoramic FD in this region. FD is not proposed as a substitute for CBCT, but as a complementary quantitative descriptor with implications for both surgical risk awareness and radiographic research methodology. © The Author(s) 2026.