Background/Objectives: Temporomandibular disorders (TMDs) are a group of musculoskeletal and neuromuscular conditions involving the temporomandibular joint (TMJ), masticatory muscles, and related anatomical structures. Although magnetic resonance imaging (MRI) is considered a noninvasive and highly informative imaging modality for assessing TMJ soft tissues, few studies have examined how TMJ structural features observed on MRI findings relate to oral function and craniofacial morphology in female patients with malocclusion. To investigate the associations among TMJ structural features, oral function, and craniofacial morphology in female patients with malocclusion, using MRI findings interpreted in conjunction with a preliminary assessment based on selected components of the DC/TMDs Axis I protocol. Methods: A total of 120 female patients (mean age: 27.3 ± 10.9 years) underwent clinical examination based on DC/TMDs Axis I and MRI-based structural characterization of the TMJ. Based on the structural features identified by MRI, patients were classified into four groups for comparison: osteoarthritis (OA), bilateral disk displacement (BDD), unilateral disk displacement (UDD), and a group with Osseous Change/Disk Displacement negative (OC/DD (−)). Occlusal contact area, occlusal force, masticatory efficiency, tongue pressure, and lip pressure were measured. Lateral cephalometric analysis assessed skeletal and dental patterns. Results: OA group exhibited significantly reduced occlusal contact area (p < 0.0083, η² = 0.12) and occlusal force (p < 0.0083, η² = 0.14) compared to the OC/DD (−) group. Cephalometric analysis revealed that both OA and BDD groups had significantly larger ANB angles (OA: 5.7°, BDD: 5.2°, OC/DD (−): 3.7°; p < 0.0083, η² = 0.21) and FMA angles (OA: 32.4°, BDD: 31.8°, OC/DD (−): 29.0°; p < 0.0083, η² = 0.17) compared to the OC/DD (−) group. No significant differences were observed in masticatory efficiency, tongue pressure, or lip pressure. Conclusions: TMJ structural abnormalities detected via MRI, especially osteoarthritis, are associated with diminished oral function and skeletal Class II and high-angle features in female patients with malocclusion. Although orthodontic treatment is not intended to manage TMDs, MRI-based structural characterization—when clinically appropriate—may aid in treatment planning by identifying underlying joint conditions.

Background: Facial asymmetry in patients with dentofacial deformity is often associated with occlusal asymmetry, functional differences in mastication, and temporomandibular joint (TMJ) conditions. However, side-to-side differences in the stability of masticatory movement and their relationship with oral function have not been fully clarified. Therefore, this study aimed to investigate differences in masticatory movement, oral function, and the prevalence of MRI-based structural features of the temporomandibular joint between the deviated and non-deviated sides in patients with facial asymmetry. Methods: Twenty-one patients with dentofacial deformity and facial asymmetry were included in this study. Oral function was evaluated by measuring occlusal contact area, occlusal force, and masticatory performance. Masticatory movement was recorded using a mandibular movement recording system, and parameters related to the masticatory path and chewing speed were calculated. The stability of masticatory movement was evaluated using the variance of these parameters across chewing cycles. Temporomandibular joint structural features were assessed using CT and MRI. Comparisons between the deviated and non-deviated sides were performed using paired statistical tests. Results: Occlusal contact area and occlusal force were significantly greater on the deviated side than on the non-deviated side (p = 0.001 and p = 0.006, respectively), whereas no significant difference was observed in masticatory performance (p = 0.211). The deviated side showed a smaller closing angle (p = 0.005) and maximum lateral amplitude (p = 0.019), indicating a more vertical chewing pattern. The stability of masticatory movement, evaluated using the variance of masticatory path and velocity parameters, was significantly greater on the deviated side (e.g., variance of cycle axis angle, p = 0.002; variance of maximum closing velocity, p = 0.006). In addition, the prevalence of imaging-based structural features of the temporomandibular joint was significantly higher on the deviated side (p = 0.016). Conclusions: Patients with dentofacial deformity and facial asymmetry were associated with functional asymmetry between the deviated and non-deviated sides. The deviated side showed greater occlusal contact area, occlusal force, and stability of masticatory movement. These findings suggest that the deviated side may be functionally favorable for mastication and may be related to a tendency toward preferential chewing behavior. However, because the habitual chewing side was not directly evaluated in the present study, this interpretation should be considered cautiously and viewed as hypothesis-generating.