The human temporomandibular joint region in different positions of the mandible

The anatomy of the human temporomandibular joint region has been investigat ed mainly under the conditions of dental occlusion. The aim of the present study was to elucidate the topographical situations in other functional pos itions such as wide-open mouth, protrusion and lateral displacement. The re spective mouth positions were adjusted before fixation and controlled by ma gnetic resonance tomography. The temporomandibular joint regions were embed ded in epoxy resin, and cut serially in the sagittal or the frontal plane. Wide-open mouth: The articular disc lies with its intermediate zone between the articular tubercle and the dorsal convexity of the condylar process, a nd thus adapts the articulating surfaces of the bones perfectly to each oth er. Massive enlargement of the retroarticular cushion is seen, whereas the loose connective tissue on the anterior side of the joint appears completel y compressed. Protrusion: The disc lies with its intermediate zone between the convexities of the condylar process and the articular eminence. On the lateral side it appears to be compressed between mandible and temporal bone . The retroarticular cushion is moderately enlarged. The anterior compartme nt of loose connective tissue is smaller than in occlusion. Lateral displac ement: On the working side the articular disc is in a stabilized position b etween the bony joint elements. The balancing condyle is in a protruded pos ition with the retroarticular cushion reaching into the dorso-lateral half of the mandibular fossa. Conclusion: Protrusion appears as the position wit h the highest mechanical stress upon the articular disc.