Disk position and the bilaminar zone of the temporomandibular joint in asymptomatic young individuals by magnetic resonance imaging

Objective. The purpose was to study the disk position of the temporomandibular joint (TMJ) in young individuals without any clinical signs or symptoms or history of internal derangement or degenerative joint disease and to study the features of the bilaminar zone of the TMJ in sagittal magnetic resonance (MR) images and the behavior of the bilaminar zone during jaw opening. Study design. MR imaging examinations of 80 TMJs of 40 symptom-free healthy subjects (20 women and 20 men) with a mean age of 26.9 years formed the basis of this study. Results. In 33 of the 40 symptom-free subjects (82.5%), there was a normal relationship between disk and condyle at occlusion, whereas 5 individuals had unilateral disk displacement and 2 had bilateral disk displacement. The superior part of the bilaminar zone could be identified in all of the 40 symptom-free subjects. The inferior band of the bilaminar zone was identified bilaterally in 57.5% of individuals and unilaterally in 20%. In 9 subjects, the inferior band of the bilaminar zone could not be identified in any of the TMJs. Conclusions. Disk displacement of the TMJ occurred in approximately 20% of the young individuals in this sample. The use of both sagittal and oblique coronal MR images is of importance for classification of the position of the disk in that the oblique coronal imaging plane rendered significant complementary information to that of the sagittal images. The identification of both the superior and the posterior band of the bilaminar zone must be considered new information. The superior band remained consistently in contact with the fossa at the open-mouth position.