Background: The aim of this work was to assess the usefulness of MR imaging in the evaluation of temporomandibular lateral disc displacement in patients with posterior occlusion and the significance of the results of MRI in the diagnosis and treatment of posterior occlusion. Material/Methods: Imaging evaluation was performed to 80 temporomandibular joints in 40 patients with posterior occlusion, of both sexes, at the age of 16-35, prior to orthodontic treatment. The imaging technique used for the evaluation of temporomandibular joints was magnetic resonance using the Signa Horizon 1.5 T System (GEMS) during rest occlusion. The evaluation was focused on bony structures of the joint and its posterior ligament. The type of joint was defined as intermediate in case of the articular tuberculum of a semicircular shape, shallow - in case of horizontally elongated ellipse, and deep - in case of vertically elongated ellipse. The symmetry of the articular space as well as the alignment of the articular disc in the frontal plane was also evaluated. The obtained data were presented in form of figures and graphs and analysed using the statistics software - BMDP New System 2.0. Results: In patients with posterior occlusion, the so-called intermediate type of temporomandibular joint was found to be the most common, whereas the symmetrical articular space occurred in 33.7% of cases. The rate of narrowed retrodiscal region was 61.2%, which was a statistically significant difference in comparison with the control group. The assessment of position of the disc in the frontal plane during occlusion revealed 12.6% of medial displacement and 6.2% of lateral displacement. Statistically significant differences between the study group and the control group were found concerning the disc position during occlusion assessed in the frontal plane (χ2=9.564; p=0.008). Statistically significant differences were confirmed concerning the width and symmetry of the articular space between the two groups - the persons with posterior occlusion and the control group (χ2=24.174; p=0.0001). In persons with posterior occlusion no significant correlation was found between the type of the joint and the position of the articular disc during occlusion in the frontal plane, that is the lateral and medial displacement (χ2=2.529; p=0.640). Correlation was found between the type of the joint and its symmetry, narrowed or widened articular space in the retrodiscal region (χ2=15.54; p<0.004). Conclusions: Diagnostic efficacy of the magnetic resonance imaging was found in the evaluation of temporomandibular joints in case of posterior occlusion. Based on the obtained results we believe that in MR of occlusion defects T2-weighted sequences can be excluded, as the application of only T1- and PD-weighted sequences is sufficient
