Magnetic resonance imaging of temporomandibular disorders: classification, prevalence and interpretation of disc displacement and deformation

Aim: To analyse the prevalence of disc displacements and deformations from MRI of symptomatic temporomandibular disorders (TMD). Methods: The study was conducted retrospectively on 192 joints of 9X patients (67 females, 31 males, mean age 29 years), who had undergone bilateral MRI (except for four who had unilateral) in the sagittal (both open and closed mouth) and coronal (closed mouth only) planes. These displacements were subdivided into static (complete anterior and posterior, partial anterolateral and anteromedial, sideways lateral and medial, anterolateral and anteromedial rotational) and dynamic (with reduction, without reduction, with incomplete reduction; non-determinable). Disc deformations were subdivided into: enlargement of the posterior band, reversed biconcave shape, biplanar (flattened) and biconvex shape. Results: Eighty per cent of patients had bilateral displacement, 15% unilateral and 5% a normally positioned disc. Complete anterior displacement was the commonest and sideways the rarest. Reduction was present in 58% of disc displacements, no reduction in 26%, incomplete reduction in 4%, while in the remaining 12%, it could not be determined. Rotational displacement was the most likely to feature reduction and sideways the least. Temporomandibular joints with no reduction were closely correlated with bone lesions. The most frequent deformation was biplanar and the rarest enlargement of the posterior band. Conclusions: There was a high prevalence of displacements and deformations. While they do not appear to be significant in inducing pain, they can predispose to the onset of osteoarthrosis.