Ultrasonographic Evaluation of Masseter Muscle Thickness and Fractal Dimension in Bruxist and Healthy Individuals

Background/Objectives: This study aimed to determine whether masseter muscle thickness and ultrasound-derived fractal dimension (FD) differ between patients with bruxism and healthy controls. Methods: Thirty patients with clinically assessed bruxism and 30 healthy volunteers (15 female, 15 male each) were included. Bruxism required a history of tooth grinding or clenching for at least one year plus at least one of three additional findings (tooth wear, masseter tenderness on palpation, morning jaw pain or headache); controls had none of these findings. Bilateral B-mode scans were acquired at rest and during maximum clenching under standardized settings. Thickness was measured with calipers, and FD was calculated by box-counting in ImageJ (version 1.54f) from three 100 × 100-pixel regions of interest per image. Intraobserver reliability was excellent for thickness (ICC = 0.967–0.980) and good for FD (ICC = 0.850–0.929). Results: Thickness was greater in bruxism patients on both sides and in both conditions (p < 0.001; bilateral mean at rest 12.95 ± 1.47 vs. 9.72 ± 1.78 mm). Bilateral mean FD was higher in bruxism patients during clenching (1.202 ± 0.027 vs. 1.182 ± 0.028; p = 0.008), and this difference remained significant after Holm correction across six FD comparisons. The resting difference (1.188 ± 0.026 vs. 1.171 ± 0.031; p = 0.029) was not robust to multiplicity correction or to exclusion of two controls whose regions of interest extended beyond the muscle. Conclusions: Clinically assessed bruxism was associated with greater masseter thickness in this sample. Bilateral mean FD was modestly higher during clenching; the resting FD difference was not robust. The reproducibility and clinical relevance of these texture measures require further study.