Flexure deformation in temporomandibular joint disk displacement without reduction may predict treatment outcome

To identify whether the direction of disk flexure deformation predicts the prognosis in cases of anterior disk displacement without reduction of painful temporomandibular joint (TMJ), the relationship between the direction of flexure, observed on pseudodynamic magnetic resonance (MR) images, and the outcome of conservative treatment using a flat occlusal splint was analysed in 40 female patients who perceived occasional or constant pain at unilateral TMJ with disk displacement without reduction. From the MR findings, 20 patients were classified as having upward flexure deformation of the disk and 20 as having downward flexure deformation. Patients' TMJ pain, masticatory muscle pain, amount of maximal mouth opening, and MR findings were evaluated before treatment. All patients were treated with a flat occlusal splint for 6 months. The patients' signs and symptoms were analysed statistically within each group before treatment and 3 and 6 months afterwards, and were also compared between the upward and downward flexure groups. There was no statistical difference between the groups before treatment, except in the amount of maximal mouth opening and the extent of disk displacement. The upward flexure group had persistent TMJ pain and tendency of delayed alleviation of masticatory muscle pain compared with the downward flexure group, although maximal opening gradually increased in both groups. Thus, the direction of the flexure in deformation of the disk, which can be observed only with pseudodynamic MR imaging, may predict the prognosis of painful disk displacement without reduction following treatment with a flat occlusal splint.